a class to store JSON values More...
#include <json.hpp>
Data Structures | |
| class | iter_impl |
| a template for a random access iterator for the basic_json class More... | |
| class | json_pointer |
| JSON Pointer. More... | |
| class | json_reverse_iterator |
| a template for a reverse iterator class More... | |
Public Types | |
| enum | parse_event_t : uint8_t { parse_event_t::object_start, parse_event_t::object_end, parse_event_t::array_start, parse_event_t::array_end, parse_event_t::key, parse_event_t::value } |
| JSON callback events. More... | |
| using | value_t = detail::value_t |
| template<typename T , typename SFINAE > | |
| using | json_serializer = JSONSerializer< T, SFINAE > |
| using | parser_callback_t = std::function< bool(int depth, parse_event_t event, basic_json &parsed)> |
| per-element parser callback type More... | |
Public Member Functions | |
| std::string | type_name () const |
| return the type as string More... | |
Static Public Member Functions | |
| static allocator_type | get_allocator () |
| returns the allocator associated with the container More... | |
| static basic_json | meta () |
| returns version information on the library More... | |
Friends | |
| template<detail::value_t > | |
| struct | detail::external_constructor |
container types | |
The canonic container types to use basic_json like any other STL container. | |
| using | value_type = basic_json |
| the type of elements in a basic_json container More... | |
| using | reference = value_type & |
| the type of an element reference More... | |
| using | const_reference = const value_type & |
| the type of an element const reference More... | |
| using | difference_type = std::ptrdiff_t |
| a type to represent differences between iterators More... | |
| using | size_type = std::size_t |
| a type to represent container sizes More... | |
| using | allocator_type = AllocatorType< basic_json > |
| the allocator type More... | |
| using | pointer = typename std::allocator_traits< allocator_type >::pointer |
| the type of an element pointer More... | |
| using | const_pointer = typename std::allocator_traits< allocator_type >::const_pointer |
| the type of an element const pointer More... | |
| using | iterator = iter_impl< basic_json > |
| an iterator for a basic_json container More... | |
| using | const_iterator = iter_impl< const basic_json > |
| a const iterator for a basic_json container More... | |
| using | reverse_iterator = json_reverse_iterator< typename basic_json::iterator > |
| a reverse iterator for a basic_json container More... | |
| using | const_reverse_iterator = json_reverse_iterator< typename basic_json::const_iterator > |
| a const reverse iterator for a basic_json container More... | |
JSON value data types | |
The data types to store a JSON value. These types are derived from the template arguments passed to class basic_json. | |
| using | object_t = ObjectType< StringType, basic_json, std::less< StringType >, AllocatorType< std::pair< const StringType, basic_json > >> |
| a type for an object More... | |
| using | array_t = ArrayType< basic_json, AllocatorType< basic_json > > |
| a type for an array More... | |
| using | string_t = StringType |
| a type for a string More... | |
| using | boolean_t = BooleanType |
| a type for a boolean More... | |
| using | number_integer_t = NumberIntegerType |
| a type for a number (integer) More... | |
| using | number_unsigned_t = NumberUnsignedType |
| a type for a number (unsigned) More... | |
| using | number_float_t = NumberFloatType |
| a type for a number (floating-point) More... | |
constructors and destructors | |
Constructors of class basic_json, copy/move constructor, copy assignment, static functions creating objects, and the destructor. | |
| static basic_json | array (std::initializer_list< basic_json > init=std::initializer_list< basic_json >()) |
| explicitly create an array from an initializer list More... | |
| static basic_json | object (std::initializer_list< basic_json > init=std::initializer_list< basic_json >()) |
| explicitly create an object from an initializer list More... | |
| basic_json (const value_t value_type) | |
| create an empty value with a given type More... | |
| basic_json (std::nullptr_t=nullptr) noexcept | |
| create a null object More... | |
| template<typename CompatibleType , typename U = detail::uncvref_t<CompatibleType>, detail::enable_if_t< not std::is_base_of< std::istream, U >::value and not std::is_same< U, basic_json_t >::value and not detail::is_basic_json_nested_type< basic_json_t, U >::value and detail::has_to_json< basic_json, U >::value, int > = 0> | |
| basic_json (CompatibleType &&val) noexcept(noexcept(JSONSerializer< U >::to_json(std::declval< basic_json_t & >(), std::forward< CompatibleType >(val)))) | |
| create a JSON value More... | |
| basic_json (std::initializer_list< basic_json > init, bool type_deduction=true, value_t manual_type=value_t::array) | |
| create a container (array or object) from an initializer list More... | |
| basic_json (size_type cnt, const basic_json &val) | |
| construct an array with count copies of given value More... | |
| template<class InputIT , typename std::enable_if< std::is_same< InputIT, typename basic_json_t::iterator >::value or std::is_same< InputIT, typename basic_json_t::const_iterator >::value, int >::type = 0> | |
| basic_json (InputIT first, InputIT last) | |
| construct a JSON container given an iterator range More... | |
| JSON_DEPRECATED | basic_json (std::istream &i, const parser_callback_t cb=nullptr) |
| construct a JSON value given an input stream More... | |
| basic_json (const basic_json &other) | |
| copy constructor More... | |
| basic_json (basic_json &&other) noexcept | |
| move constructor More... | |
| reference & | operator= (basic_json other) noexcept(std::is_nothrow_move_constructible< value_t >::value and std::is_nothrow_move_assignable< value_t >::value and std::is_nothrow_move_constructible< json_value >::value and std::is_nothrow_move_assignable< json_value >::value) |
| copy assignment More... | |
| ~basic_json () | |
| destructor More... | |
object inspection | |
| string_t | dump (const int indent=-1) const |
| serialization More... | |
| constexpr value_t | type () const noexcept |
| return the type of the JSON value (explicit) More... | |
| constexpr bool | is_primitive () const noexcept |
| return whether type is primitive More... | |
| constexpr bool | is_structured () const noexcept |
| return whether type is structured More... | |
| constexpr bool | is_null () const noexcept |
| return whether value is null More... | |
| constexpr bool | is_boolean () const noexcept |
| return whether value is a boolean More... | |
| constexpr bool | is_number () const noexcept |
| return whether value is a number More... | |
| constexpr bool | is_number_integer () const noexcept |
| return whether value is an integer number More... | |
| constexpr bool | is_number_unsigned () const noexcept |
| return whether value is an unsigned integer number More... | |
| constexpr bool | is_number_float () const noexcept |
| return whether value is a floating-point number More... | |
| constexpr bool | is_object () const noexcept |
| return whether value is an object More... | |
| constexpr bool | is_array () const noexcept |
| return whether value is an array More... | |
| constexpr bool | is_string () const noexcept |
| return whether value is a string More... | |
| constexpr bool | is_discarded () const noexcept |
| return whether value is discarded More... | |
| constexpr | operator value_t () const noexcept |
| return the type of the JSON value (implicit) More... | |
value access | |
| template<typename BasicJsonType , detail::enable_if_t< std::is_same< typename std::remove_const< BasicJsonType >::type, basic_json_t >::value, int > = 0> | |
| basic_json | get () const |
| get special-case overload More... | |
| template<typename ValueTypeCV , typename ValueType = detail::uncvref_t<ValueTypeCV>, detail::enable_if_t< not std::is_same< basic_json_t, ValueType >::value and detail::has_from_json< basic_json_t, ValueType >::value and not detail::has_non_default_from_json< basic_json_t, ValueType >::value, int > = 0> | |
| ValueType | get () const noexcept(noexcept(JSONSerializer< ValueType >::from_json(std::declval< const basic_json_t & >(), std::declval< ValueType & >()))) |
| get a value (explicit) More... | |
| template<typename ValueTypeCV , typename ValueType = detail::uncvref_t<ValueTypeCV>, detail::enable_if_t< not std::is_same< basic_json_t, ValueType >::value and detail::has_non_default_from_json< basic_json_t, ValueType >::value, int > = 0> | |
| ValueType | get () const noexcept(noexcept(JSONSerializer< ValueTypeCV >::from_json(std::declval< const basic_json_t & >()))) |
| get a value (explicit); special case More... | |
| template<typename PointerType , typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0> | |
| PointerType | get () noexcept |
| get a pointer value (explicit) More... | |
| template<typename PointerType , typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0> | |
| constexpr const PointerType | get () const noexcept |
| get a pointer value (explicit) More... | |
| template<typename PointerType , typename std::enable_if< std::is_pointer< PointerType >::value, int >::type = 0> | |
| PointerType | get_ptr () noexcept |
| get a pointer value (implicit) More... | |
| template<typename PointerType , typename std::enable_if< std::is_pointer< PointerType >::value and std::is_const< typename std::remove_pointer< PointerType >::type >::value, int >::type = 0> | |
| constexpr const PointerType | get_ptr () const noexcept |
| get a pointer value (implicit) More... | |
| template<typename ReferenceType , typename std::enable_if< std::is_reference< ReferenceType >::value, int >::type = 0> | |
| ReferenceType | get_ref () |
| get a reference value (implicit) More... | |
| template<typename ReferenceType , typename std::enable_if< std::is_reference< ReferenceType >::value and std::is_const< typename std::remove_reference< ReferenceType >::type >::value, int >::type = 0> | |
| ReferenceType | get_ref () const |
| get a reference value (implicit) More... | |
| template<typename ValueType , typename std::enable_if< not std::is_pointer< ValueType >::value and not std::is_same< ValueType, typename string_t::value_type >::value and not std::is_same< ValueType, std::initializer_list< typename string_t::value_type >>::value, int >::type = 0> | |
| operator ValueType () const | |
| get a value (implicit) More... | |
element access | |
| reference | at (size_type idx) |
| access specified array element with bounds checking More... | |
| const_reference | at (size_type idx) const |
| access specified array element with bounds checking More... | |
| reference | at (const typename object_t::key_type &key) |
| access specified object element with bounds checking More... | |
| const_reference | at (const typename object_t::key_type &key) const |
| access specified object element with bounds checking More... | |
| reference | operator[] (size_type idx) |
| access specified array element More... | |
| const_reference | operator[] (size_type idx) const |
| access specified array element More... | |
| reference | operator[] (const typename object_t::key_type &key) |
| access specified object element More... | |
| const_reference | operator[] (const typename object_t::key_type &key) const |
| read-only access specified object element More... | |
| template<typename T , std::size_t n> | |
| reference | operator[] (T *(&key)[n]) |
| access specified object element More... | |
| template<typename T , std::size_t n> | |
| const_reference | operator[] (T *(&key)[n]) const |
| read-only access specified object element More... | |
| template<typename T > | |
| reference | operator[] (T *key) |
| access specified object element More... | |
| template<typename T > | |
| const_reference | operator[] (T *key) const |
| read-only access specified object element More... | |
| template<class ValueType , typename std::enable_if< std::is_convertible< basic_json_t, ValueType >::value, int >::type = 0> | |
| ValueType | value (const typename object_t::key_type &key, ValueType default_value) const |
| access specified object element with default value More... | |
| string_t | value (const typename object_t::key_type &key, const char *default_value) const |
| overload for a default value of type const char* More... | |
| template<class ValueType , typename std::enable_if< std::is_convertible< basic_json_t, ValueType >::value, int >::type = 0> | |
| ValueType | value (const json_pointer &ptr, ValueType default_value) const |
| access specified object element via JSON Pointer with default value More... | |
| string_t | value (const json_pointer &ptr, const char *default_value) const |
| overload for a default value of type const char* More... | |
| reference | front () |
| access the first element More... | |
| const_reference | front () const |
| access the first element More... | |
| reference | back () |
| access the last element More... | |
| const_reference | back () const |
| access the last element More... | |
| template<class IteratorType , typename std::enable_if< std::is_same< IteratorType, typename basic_json_t::iterator >::value or std::is_same< IteratorType, typename basic_json_t::const_iterator >::value, int >::type = 0> | |
| IteratorType | erase (IteratorType pos) |
| remove element given an iterator More... | |
| template<class IteratorType , typename std::enable_if< std::is_same< IteratorType, typename basic_json_t::iterator >::value or std::is_same< IteratorType, typename basic_json_t::const_iterator >::value, int >::type = 0> | |
| IteratorType | erase (IteratorType first, IteratorType last) |
| remove elements given an iterator range More... | |
| size_type | erase (const typename object_t::key_type &key) |
| remove element from a JSON object given a key More... | |
| void | erase (const size_type idx) |
| remove element from a JSON array given an index More... | |
lookup | |
| iterator | find (typename object_t::key_type key) |
| find an element in a JSON object More... | |
| const_iterator | find (typename object_t::key_type key) const |
| find an element in a JSON object More... | |
| size_type | count (typename object_t::key_type key) const |
| returns the number of occurrences of a key in a JSON object More... | |
iterators | |
| static iteration_proxy< iterator > | iterator_wrapper (reference cont) |
| wrapper to access iterator member functions in range-based for More... | |
| static iteration_proxy< const_iterator > | iterator_wrapper (const_reference cont) |
| wrapper to access iterator member functions in range-based for More... | |
| iterator | begin () noexcept |
| returns an iterator to the first element More... | |
| const_iterator | begin () const noexcept |
| returns a const iterator to the first element More... | |
| const_iterator | cbegin () const noexcept |
| returns a const iterator to the first element More... | |
| iterator | end () noexcept |
| returns an iterator to one past the last element More... | |
| const_iterator | end () const noexcept |
| returns a const iterator to one past the last element More... | |
| const_iterator | cend () const noexcept |
| returns a const iterator to one past the last element More... | |
| reverse_iterator | rbegin () noexcept |
| returns an iterator to the reverse-beginning More... | |
| const_reverse_iterator | rbegin () const noexcept |
| returns a const reverse iterator to the last element More... | |
| reverse_iterator | rend () noexcept |
| returns an iterator to the reverse-end More... | |
| const_reverse_iterator | rend () const noexcept |
| returns a const reverse iterator to one before the first More... | |
| const_reverse_iterator | crbegin () const noexcept |
| returns a const reverse iterator to the last element More... | |
| const_reverse_iterator | crend () const noexcept |
| returns a const reverse iterator to one before the first More... | |
capacity | |
| bool | empty () const noexcept |
| checks whether the container is empty More... | |
| size_type | size () const noexcept |
| returns the number of elements More... | |
| size_type | max_size () const noexcept |
| returns the maximum possible number of elements More... | |
modifiers | |
| void | clear () noexcept |
| clears the contents More... | |
| void | push_back (basic_json &&val) |
| add an object to an array More... | |
| reference | operator+= (basic_json &&val) |
| add an object to an array More... | |
| void | push_back (const basic_json &val) |
| add an object to an array More... | |
| reference | operator+= (const basic_json &val) |
| add an object to an array More... | |
| void | push_back (const typename object_t::value_type &val) |
| add an object to an object More... | |
| reference | operator+= (const typename object_t::value_type &val) |
| add an object to an object More... | |
| void | push_back (std::initializer_list< basic_json > init) |
| add an object to an object More... | |
| reference | operator+= (std::initializer_list< basic_json > init) |
| add an object to an object More... | |
| template<class... Args> | |
| void | emplace_back (Args &&... args) |
| add an object to an array More... | |
| template<class... Args> | |
| std::pair< iterator, bool > | emplace (Args &&... args) |
| add an object to an object if key does not exist More... | |
| iterator | insert (const_iterator pos, const basic_json &val) |
| inserts element More... | |
| iterator | insert (const_iterator pos, basic_json &&val) |
| inserts element More... | |
| iterator | insert (const_iterator pos, size_type cnt, const basic_json &val) |
| inserts elements More... | |
| iterator | insert (const_iterator pos, const_iterator first, const_iterator last) |
| inserts elements More... | |
| iterator | insert (const_iterator pos, std::initializer_list< basic_json > ilist) |
| inserts elements More... | |
| void | swap (reference other) noexcept(std::is_nothrow_move_constructible< value_t >::value and std::is_nothrow_move_assignable< value_t >::value and std::is_nothrow_move_constructible< json_value >::value and std::is_nothrow_move_assignable< json_value >::value) |
| exchanges the values More... | |
| void | swap (array_t &other) |
| exchanges the values More... | |
| void | swap (object_t &other) |
| exchanges the values More... | |
| void | swap (string_t &other) |
| exchanges the values More... | |
lexicographical comparison operators | |
| bool | operator== (const_reference lhs, const_reference rhs) noexcept |
| comparison: equal More... | |
| template<typename ScalarType , typename std::enable_if< std::is_scalar< ScalarType >::value, int >::type = 0> | |
| bool | operator== (const_reference lhs, const ScalarType rhs) noexcept |
| comparison: equal More... | |
| template<typename ScalarType , typename std::enable_if< std::is_scalar< ScalarType >::value, int >::type = 0> | |
| bool | operator== (const ScalarType lhs, const_reference rhs) noexcept |
| comparison: equal More... | |
| bool | operator!= (const_reference lhs, const_reference rhs) noexcept |
| comparison: not equal More... | |
| template<typename ScalarType , typename std::enable_if< std::is_scalar< ScalarType >::value, int >::type = 0> | |
| bool | operator!= (const_reference lhs, const ScalarType rhs) noexcept |
| comparison: not equal More... | |
| template<typename ScalarType , typename std::enable_if< std::is_scalar< ScalarType >::value, int >::type = 0> | |
| bool | operator!= (const ScalarType lhs, const_reference rhs) noexcept |
| comparison: not equal More... | |
| bool | operator< (const_reference lhs, const_reference rhs) noexcept |
| comparison: less than More... | |
| bool | operator<= (const_reference lhs, const_reference rhs) noexcept |
| comparison: less than or equal More... | |
| bool | operator> (const_reference lhs, const_reference rhs) noexcept |
| comparison: greater than More... | |
| bool | operator>= (const_reference lhs, const_reference rhs) noexcept |
| comparison: greater than or equal More... | |
serialization | |
| std::ostream & | operator<< (std::ostream &o, const basic_json &j) |
| serialize to stream More... | |
| std::ostream & | operator>> (const basic_json &j, std::ostream &o) |
| serialize to stream More... | |
deserialization | |
| std::istream & | operator<< (basic_json &j, std::istream &i) |
| deserialize from stream More... | |
| std::istream & | operator>> (std::istream &i, basic_json &j) |
| deserialize from stream More... | |
| template<class T , std::size_t N> | |
| static basic_json | parse (T(&array)[N], const parser_callback_t cb=nullptr) |
| deserialize from an array More... | |
| template<typename CharT , typename std::enable_if< std::is_pointer< CharT >::value and std::is_integral< typename std::remove_pointer< CharT >::type >::value and sizeof(typename std::remove_pointer< CharT >::type)==1, int >::type = 0> | |
| static basic_json | parse (const CharT s, const parser_callback_t cb=nullptr) |
| deserialize from string literal More... | |
| static basic_json | parse (std::istream &i, const parser_callback_t cb=nullptr) |
| deserialize from stream More... | |
| static basic_json | parse (std::istream &&i, const parser_callback_t cb=nullptr) |
| deserialize from stream More... | |
| template<class IteratorType , typename std::enable_if< std::is_base_of< std::random_access_iterator_tag, typename std::iterator_traits< IteratorType >::iterator_category >::value, int >::type = 0> | |
| static basic_json | parse (IteratorType first, IteratorType last, const parser_callback_t cb=nullptr) |
| deserialize from an iterator range with contiguous storage More... | |
| template<class ContiguousContainer , typename std::enable_if< not std::is_pointer< ContiguousContainer >::value and std::is_base_of< std::random_access_iterator_tag, typename std::iterator_traits< decltype(std::begin(std::declval< ContiguousContainer const >()))>::iterator_category >::value, int >::type = 0> | |
| static basic_json | parse (const ContiguousContainer &c, const parser_callback_t cb=nullptr) |
| deserialize from a container with contiguous storage More... | |
binary serialization/deserialization support | |
| static std::vector< uint8_t > | to_msgpack (const basic_json &j) |
| create a MessagePack serialization of a given JSON value More... | |
| static basic_json | from_msgpack (const std::vector< uint8_t > &v, const size_t start_index=0) |
| create a JSON value from a byte vector in MessagePack format More... | |
| static std::vector< uint8_t > | to_cbor (const basic_json &j) |
| create a MessagePack serialization of a given JSON value More... | |
| static basic_json | from_cbor (const std::vector< uint8_t > &v, const size_t start_index=0) |
| create a JSON value from a byte vector in CBOR format More... | |
JSON Pointer functions | |
| reference | operator[] (const json_pointer &ptr) |
| access specified element via JSON Pointer More... | |
| const_reference | operator[] (const json_pointer &ptr) const |
| access specified element via JSON Pointer More... | |
| reference | at (const json_pointer &ptr) |
| access specified element via JSON Pointer More... | |
| const_reference | at (const json_pointer &ptr) const |
| access specified element via JSON Pointer More... | |
| basic_json | flatten () const |
| return flattened JSON value More... | |
| basic_json | unflatten () const |
| unflatten a previously flattened JSON value More... | |
JSON Patch functions | |
| static basic_json | diff (const basic_json &source, const basic_json &target, const std::string &path="") |
| creates a diff as a JSON patch More... | |
| basic_json | patch (const basic_json &json_patch) const |
| applies a JSON patch More... | |
Detailed Description
template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer>
class nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >
a class to store JSON values
- Template Parameters
-
ObjectType type for JSON objects ( std::mapby default; will be used in object_t)ArrayType type for JSON arrays ( std::vectorby default; will be used in array_t)StringType type for JSON strings and object keys ( std::stringby default; will be used in string_t)BooleanType type for JSON booleans ( boolby default; will be used in boolean_t)NumberIntegerType type for JSON integer numbers ( int64_tby default; will be used in number_integer_t)NumberUnsignedType type for JSON unsigned integer numbers ( uint64_tNumberFloatType type for JSON floating-point numbers ( doubleby default; will be used in number_float_t)AllocatorType type of the allocator to use ( std::allocatorby default)JSONSerializer the serializer to resolve internal calls to to_json()andfrom_json()(adl_serializer by default)
@requirement The class satisfies the following concept requirements:
- Basic
- DefaultConstructible: JSON values can be default constructed. The result will be a JSON null value.
- MoveConstructible: A JSON value can be constructed from an rvalue argument.
- CopyConstructible: A JSON value can be copy-constructed from an lvalue expression.
- MoveAssignable: A JSON value van be assigned from an rvalue argument.
- CopyAssignable: A JSON value can be copy-assigned from an lvalue expression.
- Destructible: JSON values can be destructed.
- Layout
- StandardLayoutType: JSON values have standard layout: All non-static data members are private and standard layout types, the class has no virtual functions or (virtual) base classes.
- Library-wide
- EqualityComparable: JSON values can be compared with
==, see operator==(const_reference,const_reference). - LessThanComparable: JSON values can be compared with
<, see operator<(const_reference,const_reference). - Swappable: Any JSON lvalue or rvalue of can be swapped with any lvalue or rvalue of other compatible types, using unqualified function call swap().
- NullablePointer: JSON values can be compared against
std::nullptr_tobjects which are used to model thenullvalue.
- EqualityComparable: JSON values can be compared with
- Container
- Container: JSON values can be used like STL containers and provide iterator access.
- ReversibleContainer; JSON values can be used like STL containers and provide reverse iterator access.
- Invariant
- The member variables m_value and m_type have the following relationship:
- If
m_type == value_t::object, thenm_value.object != nullptr. - If
m_type == value_t::array, thenm_value.array != nullptr. - If
m_type == value_t::string, thenm_value.string != nullptr. The invariants are checked by member function assert_invariant().
- If
- Since
- version 1.0.0
Member Typedef Documentation
◆ allocator_type
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::allocator_type = AllocatorType<basic_json> |
the allocator type
◆ array_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::array_t = ArrayType<basic_json, AllocatorType<basic_json> > |
a type for an array
RFC 7159 describes JSON arrays as follows:
An array is an ordered sequence of zero or more values.
To store objects in C++, a type is defined by the template parameters explained below.
- Template Parameters
-
ArrayType container type to store arrays (e.g., std::vectororstd::list)AllocatorType allocator to use for arrays (e.g., std::allocator)
Default type
With the default values for ArrayType (std::vector) and AllocatorType (std::allocator), the default value for array_t is:
Limits
RFC 7159 specifies:
An implementation may set limits on the maximum depth of nesting.
In this class, the array's limit of nesting is not constraint explicitly. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the max_size function of a JSON array.
Storage
Arrays are stored as pointers in a basic_json type. That is, for any access to array values, a pointer of type array_t* must be dereferenced.
- Since
- version 1.0.0
◆ boolean_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::boolean_t = BooleanType |
a type for a boolean
RFC 7159 implicitly describes a boolean as a type which differentiates the two literals true and false.
To store objects in C++, a type is defined by the template parameter BooleanType which chooses the type to use.
Default type
With the default values for BooleanType (bool), the default value for boolean_t is:
Storage
Boolean values are stored directly inside a basic_json type.
- Since
- version 1.0.0
◆ const_iterator
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::const_iterator = iter_impl<const basic_json> |
a const iterator for a basic_json container
◆ const_pointer
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::const_pointer = typename std::allocator_traits<allocator_type>::const_pointer |
the type of an element const pointer
◆ const_reference
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::const_reference = const value_type& |
the type of an element const reference
◆ const_reverse_iterator
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::const_reverse_iterator = json_reverse_iterator<typename basic_json::const_iterator> |
a const reverse iterator for a basic_json container
◆ difference_type
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::difference_type = std::ptrdiff_t |
a type to represent differences between iterators
◆ iterator
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::iterator = iter_impl<basic_json> |
an iterator for a basic_json container
◆ json_serializer
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::json_serializer = JSONSerializer<T, SFINAE> |
◆ number_float_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::number_float_t = NumberFloatType |
a type for a number (floating-point)
RFC 7159 describes numbers as follows:
The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.
This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.
To store floating-point numbers in C++, a type is defined by the template parameter NumberFloatType which chooses the type to use.
Default type
With the default values for NumberFloatType (double), the default value for number_float_t is:
Default behavior
- The restrictions about leading zeros is not enforced in C++. Instead, leading zeros in floating-point literals will be ignored. Internally, the value will be stored as decimal number. For instance, the C++ floating-point literal
01.2will be serialized to1.2. During deserialization, leading zeros yield an error. - Not-a-number (NaN) values will be serialized to
null.
Limits
RFC 7159 states:
This specification allows implementations to set limits on the range and precision of numbers accepted. Since software that implements IEEE 754-2008 binary64 (double precision) numbers is generally available and widely used, good interoperability can be achieved by implementations that expect no more precision or range than these provide, in the sense that implementations will approximate JSON numbers within the expected precision.
This implementation does exactly follow this approach, as it uses double precision floating-point numbers. Note values smaller than -1.79769313486232e+308 and values greater than 1.79769313486232e+308 will be stored as NaN internally and be serialized to null.
Storage
Floating-point number values are stored directly inside a basic_json type.
- See also
- number_integer_t – type for number values (integer)
- number_unsigned_t – type for number values (unsigned integer)
- Since
- version 1.0.0
◆ number_integer_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::number_integer_t = NumberIntegerType |
a type for a number (integer)
RFC 7159 describes numbers as follows:
The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.
This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.
To store integer numbers in C++, a type is defined by the template parameter NumberIntegerType which chooses the type to use.
Default type
With the default values for NumberIntegerType (int64_t), the default value for number_integer_t is:
Default behavior
- The restrictions about leading zeros is not enforced in C++. Instead, leading zeros in integer literals lead to an interpretation as octal number. Internally, the value will be stored as decimal number. For instance, the C++ integer literal
010will be serialized to8. During deserialization, leading zeros yield an error. - Not-a-number (NaN) values will be serialized to
null.
Limits
RFC 7159 specifies:
An implementation may set limits on the range and precision of numbers.
When the default type is used, the maximal integer number that can be stored is 9223372036854775807 (INT64_MAX) and the minimal integer number that can be stored is -9223372036854775808 (INT64_MIN). Integer numbers that are out of range will yield over/underflow when used in a constructor. During deserialization, too large or small integer numbers will be automatically be stored as number_unsigned_t or number_float_t.
RFC 7159 further states: > Note that when such software is used, numbers that are integers and are > in the range \([-2^{53}+1, 2^{53}-1]\) are interoperable in the sense
that implementations will agree exactly on their numeric values.
As this range is a subrange of the exactly supported range [INT64_MIN, INT64_MAX], this class's integer type is interoperable.
Storage
Integer number values are stored directly inside a basic_json type.
- See also
- number_float_t – type for number values (floating-point)
- number_unsigned_t – type for number values (unsigned integer)
- Since
- version 1.0.0
◆ number_unsigned_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::number_unsigned_t = NumberUnsignedType |
a type for a number (unsigned)
RFC 7159 describes numbers as follows:
The representation of numbers is similar to that used in most programming languages. A number is represented in base 10 using decimal digits. It contains an integer component that may be prefixed with an optional minus sign, which may be followed by a fraction part and/or an exponent part. Leading zeros are not allowed. (...) Numeric values that cannot be represented in the grammar below (such as Infinity and NaN) are not permitted.
This description includes both integer and floating-point numbers. However, C++ allows more precise storage if it is known whether the number is a signed integer, an unsigned integer or a floating-point number. Therefore, three different types, number_integer_t, number_unsigned_t and number_float_t are used.
To store unsigned integer numbers in C++, a type is defined by the template parameter NumberUnsignedType which chooses the type to use.
Default type
With the default values for NumberUnsignedType (uint64_t), the default value for number_unsigned_t is:
Default behavior
- The restrictions about leading zeros is not enforced in C++. Instead, leading zeros in integer literals lead to an interpretation as octal number. Internally, the value will be stored as decimal number. For instance, the C++ integer literal
010will be serialized to8. During deserialization, leading zeros yield an error. - Not-a-number (NaN) values will be serialized to
null.
Limits
RFC 7159 specifies:
An implementation may set limits on the range and precision of numbers.
When the default type is used, the maximal integer number that can be stored is 18446744073709551615 (UINT64_MAX) and the minimal integer number that can be stored is 0. Integer numbers that are out of range will yield over/underflow when used in a constructor. During deserialization, too large or small integer numbers will be automatically be stored as number_integer_t or number_float_t.
RFC 7159 further states: > Note that when such software is used, numbers that are integers and are > in the range \([-2^{53}+1, 2^{53}-1]\) are interoperable in the sense
that implementations will agree exactly on their numeric values.
As this range is a subrange (when considered in conjunction with the number_integer_t type) of the exactly supported range [0, UINT64_MAX], this class's integer type is interoperable.
Storage
Integer number values are stored directly inside a basic_json type.
- See also
- number_float_t – type for number values (floating-point)
- number_integer_t – type for number values (integer)
- Since
- version 2.0.0
◆ object_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::object_t = ObjectType<StringType, basic_json, std::less<StringType>, AllocatorType<std::pair<const StringType, basic_json> >> |
a type for an object
RFC 7159 describes JSON objects as follows:
An object is an unordered collection of zero or more name/value pairs, where a name is a string and a value is a string, number, boolean, null, object, or array.
To store objects in C++, a type is defined by the template parameters described below.
- Template Parameters
-
ObjectType the container to store objects (e.g., std::maporstd::unordered_map)StringType the type of the keys or names (e.g., std::string). The comparison functionstd::less<StringType>is used to order elements inside the container.AllocatorType the allocator to use for objects (e.g., std::allocator)
Default type
With the default values for ObjectType (std::map), StringType (std::string), and AllocatorType (std::allocator), the default value for object_t is:
Behavior
The choice of object_t influences the behavior of the JSON class. With the default type, objects have the following behavior:
- When all names are unique, objects will be interoperable in the sense that all software implementations receiving that object will agree on the name-value mappings.
- When the names within an object are not unique, later stored name/value pairs overwrite previously stored name/value pairs, leaving the used names unique. For instance,
{"key": 1}and{"key": 2, "key": 1}will be treated as equal and both stored as{"key": 1}. - Internally, name/value pairs are stored in lexicographical order of the names. Objects will also be serialized (see dump) in this order. For instance,
{"b": 1, "a": 2}and{"a": 2, "b": 1}will be stored and serialized as{"a": 2, "b": 1}. - When comparing objects, the order of the name/value pairs is irrelevant. This makes objects interoperable in the sense that they will not be affected by these differences. For instance,
{"b": 1, "a": 2}and{"a": 2, "b": 1}will be treated as equal.
Limits
RFC 7159 specifies:
An implementation may set limits on the maximum depth of nesting.
In this class, the object's limit of nesting is not constraint explicitly. However, a maximum depth of nesting may be introduced by the compiler or runtime environment. A theoretical limit can be queried by calling the max_size function of a JSON object.
Storage
Objects are stored as pointers in a basic_json type. That is, for any access to object values, a pointer of type object_t* must be dereferenced.
- Since
- version 1.0.0
- Note
- The order name/value pairs are added to the object is not preserved by the library. Therefore, iterating an object may return name/value pairs in a different order than they were originally stored. In fact, keys will be traversed in alphabetical order as
std::mapwithstd::lessis used by default. Please note this behavior conforms to RFC 7159, because any order implements the specified "unordered" nature of JSON objects.
◆ parser_callback_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::parser_callback_t = std::function<bool(int depth, parse_event_t event, basic_json& parsed)> |
per-element parser callback type
With a parser callback function, the result of parsing a JSON text can be influenced. When passed to parse(std::istream&, const parser_callback_t) or parse(const CharT, const parser_callback_t), it is called on certain events (passed as parse_event_t via parameter event) with a set recursion depth depth and context JSON value parsed. The return value of the callback function is a boolean indicating whether the element that emitted the callback shall be kept or not.
We distinguish six scenarios (determined by the event type) in which the callback function can be called. The following table describes the values of the parameters depth, event, and parsed.
| parameter event | description | parameter depth | parameter parsed |
|---|---|---|---|
| parse_event_t::object_start | the parser read { and started to process a JSON object | depth of the parent of the JSON object | a JSON value with type discarded |
| parse_event_t::key | the parser read a key of a value in an object | depth of the currently parsed JSON object | a JSON string containing the key |
| parse_event_t::object_end | the parser read } and finished processing a JSON object | depth of the parent of the JSON object | the parsed JSON object |
| parse_event_t::array_start | the parser read [ and started to process a JSON array | depth of the parent of the JSON array | a JSON value with type discarded |
| parse_event_t::array_end | the parser read ] and finished processing a JSON array | depth of the parent of the JSON array | the parsed JSON array |
| parse_event_t::value | the parser finished reading a JSON value | depth of the value | the parsed JSON value |
Discarding a value (i.e., returning false) has different effects depending on the context in which function was called:
- Discarded values in structured types are skipped. That is, the parser will behave as if the discarded value was never read.
- In case a value outside a structured type is skipped, it is replaced with
null. This case happens if the top-level element is skipped.
- Parameters
-
[in] depth the depth of the recursion during parsing [in] event an event of type parse_event_t indicating the context in the callback function has been called [in,out] parsed the current intermediate parse result; note that writing to this value has no effect for parse_event_t::key events
- Returns
- Whether the JSON value which called the function during parsing should be kept (
true) or not (false). In the latter case, it is either skipped completely or replaced by an empty discarded object.
- See also
- parse(std::istream&, parser_callback_t) or parse(const CharT, const parser_callback_t) for examples
- Since
- version 1.0.0
◆ pointer
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::pointer = typename std::allocator_traits<allocator_type>::pointer |
the type of an element pointer
◆ reference
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::reference = value_type& |
the type of an element reference
◆ reverse_iterator
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::reverse_iterator = json_reverse_iterator<typename basic_json::iterator> |
a reverse iterator for a basic_json container
◆ size_type
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::size_type = std::size_t |
a type to represent container sizes
◆ string_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::string_t = StringType |
a type for a string
RFC 7159 describes JSON strings as follows:
A string is a sequence of zero or more Unicode characters.
To store objects in C++, a type is defined by the template parameter described below. Unicode values are split by the JSON class into byte-sized characters during deserialization.
- Template Parameters
-
StringType the container to store strings (e.g., std::string). Note this container is used for keys/names in objects, see object_t.
Default type
With the default values for StringType (std::string), the default value for string_t is:
Encoding
Strings are stored in UTF-8 encoding. Therefore, functions like std::string::size() or std::string::length() return the number of bytes in the string rather than the number of characters or glyphs.
String comparison
RFC 7159 states:
Software implementations are typically required to test names of object members for equality. Implementations that transform the textual representation into sequences of Unicode code units and then perform the comparison numerically, code unit by code unit, are interoperable in the sense that implementations will agree in all cases on equality or inequality of two strings. For example, implementations that compare strings with escaped characters unconverted may incorrectly find that
"a\\b"and"a\u005Cb"are not equal.
This implementation is interoperable as it does compare strings code unit by code unit.
Storage
String values are stored as pointers in a basic_json type. That is, for any access to string values, a pointer of type string_t* must be dereferenced.
- Since
- version 1.0.0
◆ value_t
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::value_t = detail::value_t |
◆ value_type
| using nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::value_type = basic_json |
the type of elements in a basic_json container
Member Enumeration Documentation
◆ parse_event_t
|
strong |
JSON callback events.
This enumeration lists the parser events that can trigger calling a callback function of type parser_callback_t during parsing.
- Since
- version 1.0.0
Constructor & Destructor Documentation
◆ basic_json() [1/9]
|
inline |
create an empty value with a given type
Create an empty JSON value with a given type. The value will be default initialized with an empty value which depends on the type:
| Value type | initial value |
|---|---|
| null | null |
| boolean | false |
| string | "" |
| number | 0 |
| object | {} |
| array | [] |
- Parameters
-
[in] value_type the type of the value to create
@complexity Constant.
- Exceptions
-
std::bad_alloc if allocation for object, array, or string value fails
@liveexample{The following code shows the constructor for different value_t values,basic_json__value_t}
- Since
- version 1.0.0
◆ basic_json() [2/9]
|
inlinenoexcept |
create a null object
Create a null JSON value. It either takes a null pointer as parameter (explicitly creating null) or no parameter (implicitly creating null). The passed null pointer itself is not read – it is only used to choose the right constructor.
@complexity Constant.
@exceptionsafety No-throw guarantee: this constructor never throws exceptions.
@liveexample{The following code shows the constructor with and without a null pointer parameter.,basic_json__nullptr_t}
- Since
- version 1.0.0
◆ basic_json() [3/9]
|
inlinenoexcept |
create a JSON value
This is a "catch all" constructor for all compatible JSON types; that is, types for which a to_json() method exsits. The constructor forwards the parameter val to that method (to json_serializer<U>::to_json method with U = uncvref_t<CompatibleType>, to be exact).
Template type CompatibleType includes, but is not limited to, the following types:
- arrays: array_t and all kinds of compatible containers such as
std::vector,std::deque,std::list,std::forward_list,std::array,std::set,std::unordered_set,std::multiset, andunordered_multisetwith avalue_typefrom which a basic_json value can be constructed. - objects: object_t and all kinds of compatible associative containers such as
std::map,std::unordered_map,std::multimap, andstd::unordered_multimapwith akey_typecompatible to string_t and avalue_typefrom which a basic_json value can be constructed. - strings: string_t, string literals, and all compatible string containers can be used.
- numbers: number_integer_t, number_unsigned_t, number_float_t, and all convertible number types such as
int,size_t,int64_t,floatordoublecan be used. - boolean: boolean_t /
boolcan be used.
See the examples below.
- Template Parameters
-
CompatibleType a type such that: - CompatibleType is not derived from
std::istream, - CompatibleType is not basic_json (to avoid hijacking copy/move constructors),
- CompatibleType is not a basic_json nested type (e.g., json_pointer, iterator, etc ...)
- @ref json_serializer has a
to_json(basic_json_t&, CompatibleType&&)method
U = uncvref_t<CompatibleType> - CompatibleType is not derived from
- Parameters
-
[in] val the value to be forwarded
@complexity Usually linear in the size of the passed val, also depending on the implementation of the called to_json() method.
- Exceptions
-
what json_serializer<U>to_json()throws
@liveexample{The following code shows the constructor with several compatible types.,basic_json__CompatibleType}
- Since
- version 2.1.0
◆ basic_json() [4/9]
|
inline |
create a container (array or object) from an initializer list
Creates a JSON value of type array or object from the passed initializer list init. In case type_deduction is true (default), the type of the JSON value to be created is deducted from the initializer list init according to the following rules:
- If the list is empty, an empty JSON object value
{}is created. - If the list consists of pairs whose first element is a string, a JSON object value is created where the first elements of the pairs are treated as keys and the second elements are as values.
- In all other cases, an array is created.
The rules aim to create the best fit between a C++ initializer list and JSON values. The rationale is as follows:
- The empty initializer list is written as
{}which is exactly an empty JSON object. - C++ has now way of describing mapped types other than to list a list of pairs. As JSON requires that keys must be of type string, rule 2 is the weakest constraint one can pose on initializer lists to interpret them as an object.
- In all other cases, the initializer list could not be interpreted as JSON object type, so interpreting it as JSON array type is safe.
With the rules described above, the following JSON values cannot be expressed by an initializer list:
- the empty array (
[]): use array(std::initializer_list<basic_json>) with an empty initializer list in this case - arrays whose elements satisfy rule 2: use array(std::initializer_list<basic_json>) with the same initializer list in this case
- Note
- When used without parentheses around an empty initializer list, basic_json() is called instead of this function, yielding the JSON null value.
- Parameters
-
[in] init initializer list with JSON values [in] type_deduction internal parameter; when set to true, the type of the JSON value is deducted from the initializer list init; when set tofalse, the type provided via manual_type is forced. This mode is used by the functions array(std::initializer_list<basic_json>) and object(std::initializer_list<basic_json>).[in] manual_type internal parameter; when type_deduction is set to false, the created JSON value will use the provided type (only value_t::array and value_t::object are valid); when type_deduction is set totrue, this parameter has no effect
- Exceptions
-
std::domain_error if type_deduction is false, manual_type isvalue_t::object, but init contains an element which is not a pair whose first element is a string; example:"cannot create object from initializer list"
@complexity Linear in the size of the initializer list init.
@liveexample{The example below shows how JSON values are created from initializer lists.,basic_json__list_init_t}
- See also
- array(std::initializer_list<basic_json>) – create a JSON array value from an initializer list
- object(std::initializer_list<basic_json>) – create a JSON object value from an initializer list
- Since
- version 1.0.0
◆ basic_json() [5/9]
|
inline |
construct an array with count copies of given value
Constructs a JSON array value by creating cnt copies of a passed value. In case cnt is 0, an empty array is created. As postcondition, std::distance(begin(),end()) == cnt holds.
- Parameters
-
[in] cnt the number of JSON copies of val to create [in] val the JSON value to copy
@complexity Linear in cnt.
@liveexample{The following code shows examples for the basic_json(size_type\, const basic_json&) constructor.,basic_json__size_type_basic_json}
- Since
- version 1.0.0
◆ basic_json() [6/9]
|
inline |
construct a JSON container given an iterator range
Constructs the JSON value with the contents of the range [first, last). The semantics depends on the different types a JSON value can have:
- In case of primitive types (number, boolean, or string), first must be
begin()and last must beend(). In this case, the value is copied. Otherwise, std::out_of_range is thrown. - In case of structured types (array, object), the constructor behaves as similar versions for
std::vector. - In case of a null type, std::domain_error is thrown.
- Template Parameters
-
InputIT an input iterator type (iterator or const_iterator)
- Parameters
-
[in] first begin of the range to copy from (included) [in] last end of the range to copy from (excluded)
- Precondition
- Iterators first and last must be initialized. This precondition is enforced with an assertion.
- Exceptions
-
std::domain_error if iterators are not compatible; that is, do not belong to the same JSON value; example: "iterators are not compatible"std::out_of_range if iterators are for a primitive type (number, boolean, or string) where an out of range error can be detected easily; example: "iterators out of range"std::bad_alloc if allocation for object, array, or string fails std::domain_error if called with a null value; example: "cannot use construct with iterators from null"
@complexity Linear in distance between first and last.
@liveexample{The example below shows several ways to create JSON values by specifying a subrange with iterators.,basic_json__InputIt_InputIt}
- Since
- version 1.0.0
◆ basic_json() [7/9]
|
inlineexplicit |
construct a JSON value given an input stream
- Parameters
-
[in,out] i stream to read a serialized JSON value from [in] cb a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
- Note
- A UTF-8 byte order mark is silently ignored.
- Deprecated:
- This constructor is deprecated and will be removed in version 3.0.0 to unify the interface of the library. Deserialization will be done by stream operators or by calling one of the
parsefunctions, e.g. parse(std::istream&, const parser_callback_t). That is, calls likejson j(i);for an input stream i need to be replaced byjson j = json::parse(i);. See the example below.
@liveexample{The example below demonstrates constructing a JSON value from a std::stringstream with and without callback function.,basic_json__istream}
- Since
- version 2.0.0, deprecated in version 2.0.3, to be removed in version 3.0.0
◆ basic_json() [8/9]
|
inline |
copy constructor
Creates a copy of a given JSON value.
- Parameters
-
[in] other the JSON value to copy
@complexity Linear in the size of other.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is linear.
- As postcondition, it holds:
other == basic_json(other).
- Exceptions
-
std::bad_alloc if allocation for object, array, or string fails.
@liveexample{The following code shows an example for the copy constructor.,basic_json__basic_json}
- Since
- version 1.0.0
◆ basic_json() [9/9]
|
inlinenoexcept |
move constructor
Move constructor. Constructs a JSON value with the contents of the given value other using move semantics. It "steals" the resources from other and leaves it as JSON null value.
- Parameters
-
[in,out] other value to move to this object
- Postcondition
- other is a JSON null value
@complexity Constant.
@liveexample{The code below shows the move constructor explicitly called via std::move.,basic_json__moveconstructor}
- Since
- version 1.0.0
◆ ~basic_json()
|
inline |
destructor
Destroys the JSON value and frees all allocated memory.
@complexity Linear.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is linear.
- All stored elements are destroyed and all memory is freed.
- Since
- version 1.0.0
Member Function Documentation
◆ array()
|
inlinestatic |
explicitly create an array from an initializer list
Creates a JSON array value from a given initializer list. That is, given a list of values a, b, c, creates the JSON value [a, b, c]. If the initializer list is empty, the empty array [] is created.
- Note
- This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (basic_json(std::initializer_list<basic_json>, bool, value_t)). These cases are:
- creating an array whose elements are all pairs whose first element is a string – in this case, the initializer list constructor would create an object, taking the first elements as keys
- creating an empty array – passing the empty initializer list to the initializer list constructor yields an empty object
- Parameters
-
[in] init initializer list with JSON values to create an array from (optional)
- Returns
- JSON array value
@complexity Linear in the size of init.
@liveexample{The following code shows an example for the array function.,array}
- See also
- basic_json(std::initializer_list<basic_json>, bool, value_t) – create a JSON value from an initializer list
- object(std::initializer_list<basic_json>) – create a JSON object value from an initializer list
- Since
- version 1.0.0
◆ at() [1/6]
|
inline |
access specified array element with bounds checking
Returns a reference to the element at specified location idx, with bounds checking.
- Parameters
-
[in] idx index of the element to access
- Returns
- reference to the element at index idx
- Exceptions
-
std::domain_error if the JSON value is not an array; example: "cannot use at() with string"std::out_of_range if the index idx is out of range of the array; that is, idx >= size(); example:"array index 7 is out of range"
@complexity Constant.
@liveexample{The example below shows how array elements can be read and written using at().,at__size_type}
- Since
- version 1.0.0
◆ at() [2/6]
|
inline |
access specified array element with bounds checking
Returns a const reference to the element at specified location idx, with bounds checking.
- Parameters
-
[in] idx index of the element to access
- Returns
- const reference to the element at index idx
- Exceptions
-
std::domain_error if the JSON value is not an array; example: "cannot use at() with string"std::out_of_range if the index idx is out of range of the array; that is, idx >= size(); example:"array index 7 is out of range"
@complexity Constant.
@liveexample{The example below shows how array elements can be read using at().,at__size_type_const}
- Since
- version 1.0.0
◆ at() [3/6]
|
inline |
access specified object element with bounds checking
Returns a reference to the element at with specified key key, with bounds checking.
- Parameters
-
[in] key key of the element to access
- Returns
- reference to the element at key key
- Exceptions
-
std::domain_error if the JSON value is not an object; example: "cannot use at() with boolean"std::out_of_range if the key key is is not stored in the object; that is, find(key) == end(); example:"key "the fast" not found"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read and written using at().,at__object_t_key_type}
- See also
- operator[](const typename object_t::key_type&) for unchecked access by reference
- value() for access by value with a default value
- Since
- version 1.0.0
◆ at() [4/6]
|
inline |
access specified object element with bounds checking
Returns a const reference to the element at with specified key key, with bounds checking.
- Parameters
-
[in] key key of the element to access
- Returns
- const reference to the element at key key
- Exceptions
-
std::domain_error if the JSON value is not an object; example: "cannot use at() with boolean"std::out_of_range if the key key is is not stored in the object; that is, find(key) == end(); example:"key "the fast" not found"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read using at().,at__object_t_key_type_const}
- See also
- operator[](const typename object_t::key_type&) for unchecked access by reference
- value() for access by value with a default value
- Since
- version 1.0.0
◆ at() [5/6]
|
inline |
access specified element via JSON Pointer
Returns a reference to the element at with specified JSON pointer ptr, with bounds checking.
- Parameters
-
[in] ptr JSON pointer to the desired element
- Returns
- reference to the element pointed to by ptr
@complexity Constant.
- Exceptions
-
std::out_of_range if the JSON pointer can not be resolved std::domain_error if an array index begins with '0' std::invalid_argument if an array index was not a number
@liveexample{The behavior is shown in the example.,at_json_pointer}
- Since
- version 2.0.0
◆ at() [6/6]
|
inline |
access specified element via JSON Pointer
Returns a const reference to the element at with specified JSON pointer ptr, with bounds checking.
- Parameters
-
[in] ptr JSON pointer to the desired element
- Returns
- reference to the element pointed to by ptr
@complexity Constant.
- Exceptions
-
std::out_of_range if the JSON pointer can not be resolved std::domain_error if an array index begins with '0' std::invalid_argument if an array index was not a number
@liveexample{The behavior is shown in the example.,at_json_pointer_const}
- Since
- version 2.0.0
◆ back() [1/2]
|
inline |
access the last element
Returns a reference to the last element in the container. For a JSON container c, the expression c.back() is equivalent to
- Returns
- In case of a structured type (array or object), a reference to the last element is returned. In case of number, string, or boolean values, a reference to the value is returned.
@complexity Constant.
- Precondition
- The JSON value must not be
null(would throwstd::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).
- Postcondition
- The JSON value remains unchanged.
- Exceptions
-
std::out_of_range when called on nullvalue.
@liveexample{The following code shows an example for back().,back}
- See also
- front() – access the first element
- Since
- version 1.0.0
◆ back() [2/2]
|
inline |
access the last element
Returns a reference to the last element in the container. For a JSON container c, the expression c.back() is equivalent to
- Returns
- In case of a structured type (array or object), a reference to the last element is returned. In case of number, string, or boolean values, a reference to the value is returned.
@complexity Constant.
- Precondition
- The JSON value must not be
null(would throwstd::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).
- Postcondition
- The JSON value remains unchanged.
- Exceptions
-
std::out_of_range when called on nullvalue.
@liveexample{The following code shows an example for back().,back}
- See also
- front() – access the first element
- Since
- version 1.0.0
◆ begin() [1/2]
|
inlinenoexcept |
returns an iterator to the first element
Returns an iterator to the first element.
- Returns
- iterator to the first element
@complexity Constant.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is constant.
@liveexample{The following code shows an example for begin().,begin}
- See also
- cbegin() – returns a const iterator to the beginning
- end() – returns an iterator to the end
- cend() – returns a const iterator to the end
- Since
- version 1.0.0
◆ begin() [2/2]
|
inlinenoexcept |
returns a const iterator to the first element
Returns a const iterator to the first element.
- Returns
- const iterator to the first element
@complexity Constant.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).begin().
@liveexample{The following code shows an example for cbegin().,cbegin}
- See also
- begin() – returns an iterator to the beginning
- end() – returns an iterator to the end
- cend() – returns a const iterator to the end
- Since
- version 1.0.0
◆ cbegin()
|
inlinenoexcept |
returns a const iterator to the first element
Returns a const iterator to the first element.
- Returns
- const iterator to the first element
@complexity Constant.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).begin().
@liveexample{The following code shows an example for cbegin().,cbegin}
- See also
- begin() – returns an iterator to the beginning
- end() – returns an iterator to the end
- cend() – returns a const iterator to the end
- Since
- version 1.0.0
◆ cend()
|
inlinenoexcept |
returns a const iterator to one past the last element
Returns a const iterator to one past the last element.
- Returns
- const iterator one past the last element
@complexity Constant.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).end().
@liveexample{The following code shows an example for cend().,cend}
- See also
- end() – returns an iterator to the end
- begin() – returns an iterator to the beginning
- cbegin() – returns a const iterator to the beginning
- Since
- version 1.0.0
◆ clear()
|
inlinenoexcept |
clears the contents
Clears the content of a JSON value and resets it to the default value as if basic_json(value_t) would have been called:
| Value type | initial value |
|---|---|
| null | null |
| boolean | false |
| string | "" |
| number | 0 |
| object | {} |
| array | [] |
@complexity Linear in the size of the JSON value.
@liveexample{The example below shows the effect of clear() to different JSON types.,clear}
- Since
- version 1.0.0
◆ count()
|
inline |
returns the number of occurrences of a key in a JSON object
Returns the number of elements with key key. If ObjectType is the default std::map type, the return value will always be 0 (key was not found) or 1 (key was found).
- Note
- This method always returns
0when executed on a JSON type that is not an object.
- Parameters
-
[in] key key value of the element to count
- Returns
- Number of elements with key key. If the JSON value is not an object, the return value will be
0.
@complexity Logarithmic in the size of the JSON object.
@liveexample{The example shows how count() is used.,count}
- Since
- version 1.0.0
◆ crbegin()
|
inlinenoexcept |
returns a const reverse iterator to the last element
Returns a const iterator to the reverse-beginning; that is, the last element.
@complexity Constant.
@requirement This function helps basic_json satisfying the ReversibleContainer requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).rbegin().
@liveexample{The following code shows an example for crbegin().,crbegin}
- See also
- rbegin() – returns a reverse iterator to the beginning
- rend() – returns a reverse iterator to the end
- crend() – returns a const reverse iterator to the end
- Since
- version 1.0.0
◆ crend()
|
inlinenoexcept |
returns a const reverse iterator to one before the first
Returns a const reverse iterator to the reverse-end; that is, one before the first element.
@complexity Constant.
@requirement This function helps basic_json satisfying the ReversibleContainer requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).rend().
@liveexample{The following code shows an example for crend().,crend}
- See also
- rend() – returns a reverse iterator to the end
- rbegin() – returns a reverse iterator to the beginning
- crbegin() – returns a const reverse iterator to the beginning
- Since
- version 1.0.0
◆ diff()
|
inlinestatic |
creates a diff as a JSON patch
Creates a JSON Patch so that value source can be changed into the value target by calling patch function.
- Invariant
- For two JSON values source and target, the following code yields always
true:source.patch(diff(source, target)) == target;
- Note
- Currently, only
remove,add, andreplaceoperations are generated.
- Parameters
-
[in] source JSON value to compare from [in] target JSON value to compare against [in] path helper value to create JSON pointers
- Returns
- a JSON patch to convert the source to target
@complexity Linear in the lengths of source and target.
@liveexample{The following code shows how a JSON patch is created as a diff for two JSON values.,diff}
- See also
- patch – apply a JSON patch
- RFC 6902 (JSON Patch)
- Since
- version 2.0.0
◆ dump()
|
inline |
serialization
Serialization function for JSON values. The function tries to mimic Python's json.dumps() function, and currently supports its indent parameter.
- Parameters
-
[in] indent If indent is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of 0will only insert newlines.-1(the default) selects the most compact representation.
- Returns
- string containing the serialization of the JSON value
@complexity Linear.
@liveexample{The following example shows the effect of different indent parameters to the result of the serialization.,dump}
- Since
- version 1.0.0
◆ emplace()
|
inline |
add an object to an object if key does not exist
Inserts a new element into a JSON object constructed in-place with the given args if there is no element with the key in the container. If the function is called on a JSON null value, an empty object is created before appending the value created from args.
- Parameters
-
[in] args arguments to forward to a constructor of basic_json
- Template Parameters
-
Args compatible types to create a basic_json object
- Returns
- a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a bool denoting whether the insertion took place.
- Exceptions
-
std::domain_error when called on a type other than JSON object or null; example: "cannot use emplace() with number"
@complexity Logarithmic in the size of the container, O(log(size())).
@liveexample{The example shows how emplace() can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object. Further note how no value is added if there was already one value stored with the same key.,emplace}
- Since
- version 2.0.8
◆ emplace_back()
|
inline |
add an object to an array
Creates a JSON value from the passed parameters args to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending the value created from args.
- Parameters
-
[in] args arguments to forward to a constructor of basic_json
- Template Parameters
-
Args compatible types to create a basic_json object
- Exceptions
-
std::domain_error when called on a type other than JSON array or null; example: "cannot use emplace_back() with number"
@complexity Amortized constant.
@liveexample{The example shows how push_back() can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,emplace_back}
- Since
- version 2.0.8
◆ empty()
|
inlinenoexcept |
checks whether the container is empty
Checks if a JSON value has no elements.
- Returns
- The return value depends on the different types and is defined as follows:
Value type return value null trueboolean falsestring falsenumber falseobject result of function object_t::empty()array result of function array_t::empty()
- Note
- This function does not return whether a string stored as JSON value is empty - it returns whether the JSON container itself is empty which is false in the case of a string.
@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their empty() functions have constant complexity.
@requirement This function helps basic_json satisfying the Container requirements:
@liveexample{The following code uses empty() to check if a JSON object contains any elements.,empty}
- See also
- size() – returns the number of elements
- Since
- version 1.0.0
◆ end() [1/2]
|
inlinenoexcept |
returns an iterator to one past the last element
Returns an iterator to one past the last element.
- Returns
- iterator one past the last element
@complexity Constant.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is constant.
@liveexample{The following code shows an example for end().,end}
- See also
- cend() – returns a const iterator to the end
- begin() – returns an iterator to the beginning
- cbegin() – returns a const iterator to the beginning
- Since
- version 1.0.0
◆ end() [2/2]
|
inlinenoexcept |
returns a const iterator to one past the last element
Returns a const iterator to one past the last element.
- Returns
- const iterator one past the last element
@complexity Constant.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).end().
@liveexample{The following code shows an example for cend().,cend}
- See also
- end() – returns an iterator to the end
- begin() – returns an iterator to the beginning
- cbegin() – returns a const iterator to the beginning
- Since
- version 1.0.0
◆ erase() [1/4]
|
inline |
remove element given an iterator
Removes the element specified by iterator pos. The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos.
If called on a primitive type other than null, the resulting JSON value will be null.
- Parameters
-
[in] pos iterator to the element to remove
- Returns
- Iterator following the last removed element. If the iterator pos refers to the last element, the
end()iterator is returned.
- Template Parameters
-
IteratorType an iterator or const_iterator
- Postcondition
- Invalidates iterators and references at or after the point of the erase, including the
end()iterator.
- Exceptions
-
std::domain_error if called on a nullvalue; example:"cannot use erase() with null"std::domain_error if called on an iterator which does not belong to the current JSON value; example: "iterator does not fit current value"std::out_of_range if called on a primitive type with invalid iterator (i.e., any iterator which is not begin()); example:"iterator out of range"
@complexity The complexity depends on the type:
- objects: amortized constant
- arrays: linear in distance between pos and the end of the container
- strings: linear in the length of the string
- other types: constant
@liveexample{The example shows the result of erase() for different JSON types.,erase__IteratorType}
- See also
- erase(IteratorType, IteratorType) – removes the elements in the given range
- erase(const typename object_t::key_type&) – removes the element from an object at the given key
- erase(const size_type) – removes the element from an array at the given index
- Since
- version 1.0.0
◆ erase() [2/4]
|
inline |
remove elements given an iterator range
Removes the element specified by the range [first; last). The iterator first does not need to be dereferenceable if first == last: erasing an empty range is a no-op.
If called on a primitive type other than null, the resulting JSON value will be null.
- Parameters
-
[in] first iterator to the beginning of the range to remove [in] last iterator past the end of the range to remove
- Returns
- Iterator following the last removed element. If the iterator second refers to the last element, the
end()iterator is returned.
- Template Parameters
-
IteratorType an iterator or const_iterator
- Postcondition
- Invalidates iterators and references at or after the point of the erase, including the
end()iterator.
- Exceptions
-
std::domain_error if called on a nullvalue; example:"cannot use erase() with null"std::domain_error if called on iterators which does not belong to the current JSON value; example: "iterators do not fit current value"std::out_of_range if called on a primitive type with invalid iterators (i.e., if first != begin()andlast != end()); example:"iterators out of range"
@complexity The complexity depends on the type:
- objects:
log(size()) + std::distance(first, last) - arrays: linear in the distance between first and last, plus linear in the distance between last and end of the container
- strings: linear in the length of the string
- other types: constant
@liveexample{The example shows the result of erase() for different JSON types.,erase__IteratorType_IteratorType}
- See also
- erase(IteratorType) – removes the element at a given position
- erase(const typename object_t::key_type&) – removes the element from an object at the given key
- erase(const size_type) – removes the element from an array at the given index
- Since
- version 1.0.0
◆ erase() [3/4]
|
inline |
remove element from a JSON object given a key
Removes elements from a JSON object with the key value key.
- Parameters
-
[in] key value of the elements to remove
- Returns
- Number of elements removed. If ObjectType is the default
std::maptype, the return value will always be0(key was not found) or1(key was found).
- Postcondition
- References and iterators to the erased elements are invalidated. Other references and iterators are not affected.
- Exceptions
-
std::domain_error when called on a type other than JSON object; example: "cannot use erase() with null"
@complexity log(size()) + count(key)
@liveexample{The example shows the effect of erase().,erase__key_type}
- See also
- erase(IteratorType) – removes the element at a given position
- erase(IteratorType, IteratorType) – removes the elements in the given range
- erase(const size_type) – removes the element from an array at the given index
- Since
- version 1.0.0
◆ erase() [4/4]
|
inline |
remove element from a JSON array given an index
Removes element from a JSON array at the index idx.
- Parameters
-
[in] idx index of the element to remove
- Exceptions
-
std::domain_error when called on a type other than JSON array; example: "cannot use erase() with null"std::out_of_range when idx >= size(); example:"array index 17 is out of range"
@complexity Linear in distance between idx and the end of the container.
@liveexample{The example shows the effect of erase().,erase__size_type}
- See also
- erase(IteratorType) – removes the element at a given position
- erase(IteratorType, IteratorType) – removes the elements in the given range
- erase(const typename object_t::key_type&) – removes the element from an object at the given key
- Since
- version 1.0.0
◆ find() [1/2]
|
inline |
find an element in a JSON object
Finds an element in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, end() is returned.
- Note
- This method always returns end() when executed on a JSON type that is not an object.
- Parameters
-
[in] key key value of the element to search for
- Returns
- Iterator to an element with key equivalent to key. If no such element is found or the JSON value is not an object, past-the-end (see end()) iterator is returned.
@complexity Logarithmic in the size of the JSON object.
@liveexample{The example shows how find() is used.,find__key_type}
- Since
- version 1.0.0
◆ find() [2/2]
|
inline |
find an element in a JSON object
find an element in a JSON object Finds an element in a JSON object with key equivalent to key. If the element is not found or the JSON value is not an object, end() is returned.
- Note
- This method always returns end() when executed on a JSON type that is not an object.
- Parameters
-
[in] key key value of the element to search for
- Returns
- Iterator to an element with key equivalent to key. If no such element is found or the JSON value is not an object, past-the-end (see end()) iterator is returned.
@complexity Logarithmic in the size of the JSON object.
@liveexample{The example shows how find() is used.,find__key_type}
- Since
- version 1.0.0
◆ flatten()
|
inline |
return flattened JSON value
The function creates a JSON object whose keys are JSON pointers (see RFC 6901) and whose values are all primitive. The original JSON value can be restored using the unflatten() function.
- Returns
- an object that maps JSON pointers to primitive values
- Note
- Empty objects and arrays are flattened to
nulland will not be reconstructed correctly by the unflatten() function.
@complexity Linear in the size the JSON value.
@liveexample{The following code shows how a JSON object is flattened to an object whose keys consist of JSON pointers.,flatten}
- See also
- unflatten() for the reverse function
- Since
- version 2.0.0
◆ from_cbor()
|
inlinestatic |
create a JSON value from a byte vector in CBOR format
Deserializes a given byte vector v to a JSON value using the CBOR (Concise Binary Object Representation) serialization format.
- Parameters
-
[in] v a byte vector in CBOR format [in] start_index the index to start reading from v (0 by default)
- Returns
- deserialized JSON value
- Exceptions
-
std::invalid_argument if unsupported features from CBOR were used in the given vector v or if the input is not valid MessagePack std::out_of_range if the given vector ends prematurely
@complexity Linear in the size of the byte vector v.
@liveexample{The example shows the deserialization of a byte vector in CBOR format to a JSON value.,from_cbor}
- See also
- http://cbor.io
- to_cbor(const basic_json&) for the analogous serialization
- from_msgpack(const std::vector<uint8_t>&, const size_t) for the related MessagePack format
- Since
- version 2.0.9, parameter start_index since 2.1.1
◆ from_msgpack()
|
inlinestatic |
create a JSON value from a byte vector in MessagePack format
Deserializes a given byte vector v to a JSON value using the MessagePack serialization format.
- Parameters
-
[in] v a byte vector in MessagePack format [in] start_index the index to start reading from v (0 by default)
- Returns
- deserialized JSON value
- Exceptions
-
std::invalid_argument if unsupported features from MessagePack were used in the given vector v or if the input is not valid MessagePack std::out_of_range if the given vector ends prematurely
@complexity Linear in the size of the byte vector v.
@liveexample{The example shows the deserialization of a byte vector in MessagePack format to a JSON value.,from_msgpack}
- See also
- http://msgpack.org
- to_msgpack(const basic_json&) for the analogous serialization
- from_cbor(const std::vector<uint8_t>&, const size_t) for the related CBOR format
- Since
- version 2.0.9, parameter start_index since 2.1.1
◆ front() [1/2]
|
inline |
access the first element
Returns a reference to the first element in the container. For a JSON container c, the expression c.front() is equivalent to *c.begin().
- Returns
- In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, or boolean values, a reference to the value is returned.
@complexity Constant.
- Precondition
- The JSON value must not be
null(would throwstd::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).
- Postcondition
- The JSON value remains unchanged.
- Exceptions
-
std::out_of_range when called on nullvalue
@liveexample{The following code shows an example for front().,front}
- See also
- back() – access the last element
- Since
- version 1.0.0
◆ front() [2/2]
|
inline |
access the first element
Returns a reference to the first element in the container. For a JSON container c, the expression c.front() is equivalent to *c.begin().
- Returns
- In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, or boolean values, a reference to the value is returned.
@complexity Constant.
- Precondition
- The JSON value must not be
null(would throwstd::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).
- Postcondition
- The JSON value remains unchanged.
- Exceptions
-
std::out_of_range when called on nullvalue
@liveexample{The following code shows an example for front().,front}
- See also
- back() – access the last element
- Since
- version 1.0.0
◆ get() [1/5]
|
inline |
get special-case overload
This overloads avoids a lot of template boilerplate, it can be seen as the identity method
- Template Parameters
-
BasicJsonType == basic_json
- Returns
- a copy of *this
@complexity Constant.
- Since
- version 2.1.0
◆ get() [2/5]
|
inlinenoexcept |
get a value (explicit)
Explicit type conversion between the JSON value and a compatible value which is CopyConstructible and DefaultConstructible. The value is converted by calling the json_serializer<ValueType> from_json() method.
The function is equivalent to executing
This overloads is chosen if:
- ValueType is not basic_json,
- json_serializer<ValueType> has a
from_json()method of the formvoid from_json(const @ref basic_json&, ValueType&), and - json_serializer<ValueType> does not have a
from_json()method of the formValueType from_json(const @ref basic_json&)
- Template Parameters
-
ValueTypeCV the provided value type ValueType the returned value type
- Returns
- copy of the JSON value, converted to ValueType
- Exceptions
-
what json_serializer<ValueType> from_json()method throws
@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,get__ValueType_const}
- Since
- version 2.1.0
◆ get() [3/5]
|
inlinenoexcept |
get a value (explicit); special case
Explicit type conversion between the JSON value and a compatible value which is not CopyConstructible and not DefaultConstructible. The value is converted by calling the json_serializer<ValueType> from_json() method.
The function is equivalent to executing
This overloads is chosen if:
- ValueType is not basic_json and
- json_serializer<ValueType> has a
from_json()method of the formValueType from_json(const @ref basic_json&)
- Note
- If json_serializer<ValueType> has both overloads of
from_json(), this one is chosen.
- Template Parameters
-
ValueTypeCV the provided value type ValueType the returned value type
- Returns
- copy of the JSON value, converted to ValueType
- Exceptions
-
what json_serializer<ValueType> from_json()method throws
- Since
- version 2.1.0
◆ get() [4/5]
|
inlinenoexcept |
get a pointer value (explicit)
Explicit pointer access to the internally stored JSON value. No copies are made.
- Warning
- The pointer becomes invalid if the underlying JSON object changes.
- Template Parameters
-
PointerType pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t.
- Returns
- pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value;
nullptrotherwise
@complexity Constant.
@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get__PointerType}
- See also
- get_ptr() for explicit pointer-member access
- Since
- version 1.0.0
◆ get() [5/5]
|
inlinenoexcept |
get a pointer value (explicit)
get a pointer value (explicit) Explicit pointer access to the internally stored JSON value. No copies are made.
- Warning
- The pointer becomes invalid if the underlying JSON object changes.
- Template Parameters
-
PointerType pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t.
- Returns
- pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value;
nullptrotherwise
@complexity Constant.
@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get__PointerType}
- See also
- get_ptr() for explicit pointer-member access
- Since
- version 1.0.0
◆ get_allocator()
|
inlinestatic |
returns the allocator associated with the container
◆ get_ptr() [1/2]
|
inlinenoexcept |
get a pointer value (implicit)
Implicit pointer access to the internally stored JSON value. No copies are made.
- Warning
- Writing data to the pointee of the result yields an undefined state.
- Template Parameters
-
PointerType pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t. Enforced by a static assertion.
- Returns
- pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value;
nullptrotherwise
@complexity Constant.
@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get_ptr}
- Since
- version 1.0.0
◆ get_ptr() [2/2]
|
inlinenoexcept |
get a pointer value (implicit)
get a pointer value (implicit) Implicit pointer access to the internally stored JSON value. No copies are made.
- Warning
- Writing data to the pointee of the result yields an undefined state.
- Template Parameters
-
PointerType pointer type; must be a pointer to array_t, object_t, string_t, boolean_t, number_integer_t, number_unsigned_t, or number_float_t. Enforced by a static assertion.
- Returns
- pointer to the internally stored JSON value if the requested pointer type PointerType fits to the JSON value;
nullptrotherwise
@complexity Constant.
@liveexample{The example below shows how pointers to internal values of a JSON value can be requested. Note that no type conversions are made and a nullptr is returned if the value and the requested pointer type does not match.,get_ptr}
- Since
- version 1.0.0
◆ get_ref() [1/2]
|
inline |
get a reference value (implicit)
Implicit reference access to the internally stored JSON value. No copies are made.
- Warning
- Writing data to the referee of the result yields an undefined state.
- Template Parameters
-
ReferenceType reference type; must be a reference to array_t, object_t, string_t, boolean_t, number_integer_t, or number_float_t. Enforced by static assertion.
- Returns
- reference to the internally stored JSON value if the requested reference type ReferenceType fits to the JSON value; throws std::domain_error otherwise
- Exceptions
-
std::domain_error in case passed type ReferenceType is incompatible with the stored JSON value
@complexity Constant.
@liveexample{The example shows several calls to get_ref().,get_ref}
- Since
- version 1.1.0
◆ get_ref() [2/2]
|
inline |
get a reference value (implicit)
get a reference value (implicit) Implicit reference access to the internally stored JSON value. No copies are made.
- Warning
- Writing data to the referee of the result yields an undefined state.
- Template Parameters
-
ReferenceType reference type; must be a reference to array_t, object_t, string_t, boolean_t, number_integer_t, or number_float_t. Enforced by static assertion.
- Returns
- reference to the internally stored JSON value if the requested reference type ReferenceType fits to the JSON value; throws std::domain_error otherwise
- Exceptions
-
std::domain_error in case passed type ReferenceType is incompatible with the stored JSON value
@complexity Constant.
@liveexample{The example shows several calls to get_ref().,get_ref}
- Since
- version 1.1.0
◆ insert() [1/5]
|
inline |
inserts element
Inserts element val before iterator pos.
- Parameters
-
[in] pos iterator before which the content will be inserted; may be the end() iterator [in] val element to insert
- Returns
- iterator pointing to the inserted val.
- Exceptions
-
std::domain_error if called on JSON values other than arrays; example: "cannot use insert() with string"std::domain_error if pos is not an iterator of *this; example: "iterator does not fit current value"
@complexity Constant plus linear in the distance between pos and end of the container.
@liveexample{The example shows how insert() is used.,insert}
- Since
- version 1.0.0
◆ insert() [2/5]
|
inline |
inserts element
inserts element Inserts element val before iterator pos.
- Parameters
-
[in] pos iterator before which the content will be inserted; may be the end() iterator [in] val element to insert
- Returns
- iterator pointing to the inserted val.
- Exceptions
-
std::domain_error if called on JSON values other than arrays; example: "cannot use insert() with string"std::domain_error if pos is not an iterator of *this; example: "iterator does not fit current value"
@complexity Constant plus linear in the distance between pos and end of the container.
@liveexample{The example shows how insert() is used.,insert}
- Since
- version 1.0.0
◆ insert() [3/5]
|
inline |
inserts elements
Inserts cnt copies of val before iterator pos.
- Parameters
-
[in] pos iterator before which the content will be inserted; may be the end() iterator [in] cnt number of copies of val to insert [in] val element to insert
- Returns
- iterator pointing to the first element inserted, or pos if
cnt==0
- Exceptions
-
std::domain_error if called on JSON values other than arrays; example: "cannot use insert() with string"std::domain_error if pos is not an iterator of *this; example: "iterator does not fit current value"
@complexity Linear in cnt plus linear in the distance between pos and end of the container.
@liveexample{The example shows how insert() is used.,insert__count}
- Since
- version 1.0.0
◆ insert() [4/5]
|
inline |
inserts elements
Inserts elements from range [first, last) before iterator pos.
- Parameters
-
[in] pos iterator before which the content will be inserted; may be the end() iterator [in] first begin of the range of elements to insert [in] last end of the range of elements to insert
- Exceptions
-
std::domain_error if called on JSON values other than arrays; example: "cannot use insert() with string"std::domain_error if pos is not an iterator of *this; example: "iterator does not fit current value"std::domain_error if first and last do not belong to the same JSON value; example: "iterators do not fit"std::domain_error if first or last are iterators into container for which insert is called; example: "passed iterators may not belong to container"
- Returns
- iterator pointing to the first element inserted, or pos if
first==last
@complexity Linear in std::distance(first, last) plus linear in the distance between pos and end of the container.
@liveexample{The example shows how insert() is used.,insert__range}
- Since
- version 1.0.0
◆ insert() [5/5]
|
inline |
inserts elements
Inserts elements from initializer list ilist before iterator pos.
- Parameters
-
[in] pos iterator before which the content will be inserted; may be the end() iterator [in] ilist initializer list to insert the values from
- Exceptions
-
std::domain_error if called on JSON values other than arrays; example: "cannot use insert() with string"std::domain_error if pos is not an iterator of *this; example: "iterator does not fit current value"
- Returns
- iterator pointing to the first element inserted, or pos if
ilistis empty
@complexity Linear in ilist.size() plus linear in the distance between pos and end of the container.
@liveexample{The example shows how insert() is used.,insert__ilist}
- Since
- version 1.0.0
◆ is_array()
|
inlinenoexcept |
return whether value is an array
This function returns true iff the JSON value is an array.
- Returns
trueif type is array,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_array() for all JSON types.,is_array}
- Since
- version 1.0.0
◆ is_boolean()
|
inlinenoexcept |
return whether value is a boolean
This function returns true iff the JSON value is a boolean.
- Returns
trueif type is boolean,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_boolean() for all JSON types.,is_boolean}
- Since
- version 1.0.0
◆ is_discarded()
|
inlinenoexcept |
return whether value is discarded
This function returns true iff the JSON value was discarded during parsing with a callback function (see parser_callback_t).
- Note
- This function will always be
falsefor JSON values after parsing. That is, discarded values can only occur during parsing, but will be removed when inside a structured value or replaced by null in other cases.
- Returns
trueif type is discarded,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_discarded() for all JSON types.,is_discarded}
- Since
- version 1.0.0
◆ is_null()
|
inlinenoexcept |
return whether value is null
This function returns true iff the JSON value is null.
- Returns
trueif type is null,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_null() for all JSON types.,is_null}
- Since
- version 1.0.0
◆ is_number()
|
inlinenoexcept |
return whether value is a number
This function returns true iff the JSON value is a number. This includes both integer and floating-point values.
- Returns
trueif type is number (regardless whether integer, unsigned integer or floating-type),falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_number() for all JSON types.,is_number}
- See also
- is_number_integer() – check if value is an integer or unsigned integer number
- is_number_unsigned() – check if value is an unsigned integer number
- is_number_float() – check if value is a floating-point number
- Since
- version 1.0.0
◆ is_number_float()
|
inlinenoexcept |
return whether value is a floating-point number
This function returns true iff the JSON value is a floating-point number. This excludes integer and unsigned integer values.
- Returns
trueif type is a floating-point number,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_number_float() for all JSON types.,is_number_float}
- See also
- is_number() – check if value is number
- is_number_integer() – check if value is an integer number
- is_number_unsigned() – check if value is an unsigned integer number
- Since
- version 1.0.0
◆ is_number_integer()
|
inlinenoexcept |
return whether value is an integer number
This function returns true iff the JSON value is an integer or unsigned integer number. This excludes floating-point values.
- Returns
trueif type is an integer or unsigned integer number,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_number_integer() for all JSON types.,is_number_integer}
- See also
- is_number() – check if value is a number
- is_number_unsigned() – check if value is an unsigned integer number
- is_number_float() – check if value is a floating-point number
- Since
- version 1.0.0
◆ is_number_unsigned()
|
inlinenoexcept |
return whether value is an unsigned integer number
This function returns true iff the JSON value is an unsigned integer number. This excludes floating-point and (signed) integer values.
- Returns
trueif type is an unsigned integer number,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_number_unsigned() for all JSON types.,is_number_unsigned}
- See also
- is_number() – check if value is a number
- is_number_integer() – check if value is an integer or unsigned integer number
- is_number_float() – check if value is a floating-point number
- Since
- version 2.0.0
◆ is_object()
|
inlinenoexcept |
return whether value is an object
This function returns true iff the JSON value is an object.
- Returns
trueif type is object,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_object() for all JSON types.,is_object}
- Since
- version 1.0.0
◆ is_primitive()
|
inlinenoexcept |
return whether type is primitive
This function returns true iff the JSON type is primitive (string, number, boolean, or null).
- Returns
trueif type is primitive (string, number, boolean, or null),falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_primitive() for all JSON types.,is_primitive}
- See also
- is_structured() – returns whether JSON value is structured
-
is_null() – returns whether JSON value is
null - is_string() – returns whether JSON value is a string
- is_boolean() – returns whether JSON value is a boolean
- is_number() – returns whether JSON value is a number
- Since
- version 1.0.0
◆ is_string()
|
inlinenoexcept |
return whether value is a string
This function returns true iff the JSON value is a string.
- Returns
trueif type is string,falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_string() for all JSON types.,is_string}
- Since
- version 1.0.0
◆ is_structured()
|
inlinenoexcept |
return whether type is structured
This function returns true iff the JSON type is structured (array or object).
- Returns
trueif type is structured (array or object),falseotherwise.
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies is_structured() for all JSON types.,is_structured}
- See also
- is_primitive() – returns whether value is primitive
- is_array() – returns whether value is an array
- is_object() – returns whether value is an object
- Since
- version 1.0.0
◆ iterator_wrapper() [1/2]
|
inlinestatic |
wrapper to access iterator member functions in range-based for
This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.
- Note
- The name of this function is not yet final and may change in the future.
◆ iterator_wrapper() [2/2]
|
inlinestatic |
wrapper to access iterator member functions in range-based for
This function allows to access iterator::key() and iterator::value() during range-based for loops. In these loops, a reference to the JSON values is returned, so there is no access to the underlying iterator.
- Note
- The name of this function is not yet final and may change in the future.
◆ max_size()
|
inlinenoexcept |
returns the maximum possible number of elements
Returns the maximum number of elements a JSON value is able to hold due to system or library implementation limitations, i.e. std::distance(begin(), end()) for the JSON value.
- Returns
- The return value depends on the different types and is defined as follows:
Value type return value null 0(same assize())boolean 1(same assize())string 1(same assize())number 1(same assize())object result of function object_t::max_size()array result of function array_t::max_size()
@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their max_size() functions have constant complexity.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is constant.
- Has the semantics of returning
b.size()wherebis the largest possible JSON value.
@liveexample{The following code calls max_size() on the different value types. Note the output is implementation specific.,max_size}
- See also
- size() – returns the number of elements
- Since
- version 1.0.0
◆ meta()
|
inlinestatic |
returns version information on the library
This function returns a JSON object with information about the library, including the version number and information on the platform and compiler.
- Returns
- JSON object holding version information
key description compilerInformation on the used compiler. It is an object with the following keys: c++(the used C++ standard),family(the compiler family; possible values areclang,icc,gcc,ilecpp,msvc,pgcpp,sunpro, andunknown), andversion(the compiler version).copyrightThe copyright line for the library as string. nameThe name of the library as string. platformThe used platform as string. Possible values are win32,linux,apple,unix, andunknown.urlThe URL of the project as string. versionThe version of the library. It is an object with the following keys: major,minor, andpatchas defined by Semantic Versioning, andstring(the version string).
@liveexample{The following code shows an example output of the meta() function.,meta}
@complexity Constant.
- Since
- 2.1.0
◆ object()
|
inlinestatic |
explicitly create an object from an initializer list
Creates a JSON object value from a given initializer list. The initializer lists elements must be pairs, and their first elements must be strings. If the initializer list is empty, the empty object {} is created.
- Note
- This function is only added for symmetry reasons. In contrast to the related function array(std::initializer_list<basic_json>), there are no cases which can only be expressed by this function. That is, any initializer list init can also be passed to the initializer list constructor basic_json(std::initializer_list<basic_json>, bool, value_t).
- Parameters
-
[in] init initializer list to create an object from (optional)
- Returns
- JSON object value
- Exceptions
-
std::domain_error if init is not a pair whose first elements are strings; thrown by basic_json(std::initializer_list<basic_json>, bool, value_t)
@complexity Linear in the size of init.
@liveexample{The following code shows an example for the object function.,object}
- See also
- basic_json(std::initializer_list<basic_json>, bool, value_t) – create a JSON value from an initializer list
- array(std::initializer_list<basic_json>) – create a JSON array value from an initializer list
- Since
- version 1.0.0
◆ operator value_t()
|
inlinenoexcept |
return the type of the JSON value (implicit)
Implicitly return the type of the JSON value as a value from the value_t enumeration.
- Returns
- the type of the JSON value
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies the value_t operator for all JSON types.,operator__value_t}
- Since
- version 1.0.0
◆ operator ValueType()
|
inline |
get a value (implicit)
Implicit type conversion between the JSON value and a compatible value. The call is realized by calling get() const.
- Template Parameters
-
ValueType non-pointer type compatible to the JSON value, for instance intfor JSON integer numbers,boolfor JSON booleans, orstd::vectortypes for JSON arrays. The character type of string_t as well as an initializer list of this type is excluded to avoid ambiguities as these types implicitly convert tostd::string.
- Returns
- copy of the JSON value, converted to type ValueType
- Exceptions
-
std::domain_error in case passed type ValueType is incompatible to JSON, thrown by get() const
@complexity Linear in the size of the JSON value.
@liveexample{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers\, (2) A JSON array can be converted to a standard std::vector<short>\, (3) A JSON object can be converted to C++ associative containers such as std::unordered_map<std::string\, json>.,operator__ValueType}
- Since
- version 1.0.0
◆ operator+=() [1/4]
|
inline |
add an object to an array
add an object to an array Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.
- Parameters
-
[in] val the value to add to the JSON array
- Exceptions
-
std::domain_error when called on a type other than JSON array or null; example: "cannot use push_back() with number"
@complexity Amortized constant.
@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}
- Since
- version 1.0.0
◆ operator+=() [2/4]
|
inline |
add an object to an array
add an object to an array Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.
- Parameters
-
[in] val the value to add to the JSON array
- Exceptions
-
std::domain_error when called on a type other than JSON array or null; example: "cannot use push_back() with number"
@complexity Amortized constant.
@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}
- Since
- version 1.0.0
◆ operator+=() [3/4]
|
inline |
add an object to an object
add an object to an object Inserts the given element val to the JSON object. If the function is called on a JSON null value, an empty object is created before inserting val.
- Parameters
-
[in] val the value to add to the JSON object
- Exceptions
-
std::domain_error when called on a type other than JSON object or null; example: "cannot use push_back() with number"
@complexity Logarithmic in the size of the container, O(log(size())).
@liveexample{The example shows how push_back() and += can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object.,push_back__object_t__value}
- Since
- version 1.0.0
◆ operator+=() [4/4]
|
inline |
add an object to an object
add an object to an object This function allows to use push_back with an initializer list. In case
- the current value is an object,
- the initializer list init contains only two elements, and
- the first element of init is a string,
init is converted into an object element and added using push_back(const typename object_t::value_type&). Otherwise, init is converted to a JSON value and added using push_back(basic_json&&).
- Parameters
-
init an initializer list
@complexity Linear in the size of the initializer list init.
- Note
- This function is required to resolve an ambiguous overload error, because pairs like
{"key", "value"}can be both interpreted asobject_t::value_typeorstd::initializer_list<basic_json>, see https://github.com/nlohmann/json/issues/235 for more information.
@liveexample{The example shows how initializer lists are treated as objects when possible.,push_back__initializer_list}
◆ operator=()
|
inlinenoexcept |
copy assignment
Copy assignment operator. Copies a JSON value via the "copy and swap" strategy: It is expressed in terms of the copy constructor, destructor, and the swap() member function.
- Parameters
-
[in] other value to copy from
@complexity Linear.
@requirement This function helps basic_json satisfying the Container requirements:
- The complexity is linear.
@liveexample{The code below shows and example for the copy assignment. It creates a copy of value a which is then swapped with b. Finally\, the copy of a (which is the null value after the swap) is destroyed.,basic_json__copyassignment}
- Since
- version 1.0.0
◆ operator[]() [1/10]
|
inline |
access specified array element
Returns a reference to the element at specified location idx.
- Note
- If idx is beyond the range of the array (i.e.,
idx >= size()), then the array is silently filled up withnullvalues to makeidxa valid reference to the last stored element.
- Parameters
-
[in] idx index of the element to access
- Returns
- reference to the element at index idx
- Exceptions
-
std::domain_error if JSON is not an array or null; example: "cannot use operator[] with string"
@complexity Constant if idx is in the range of the array. Otherwise linear in idx - size().
@liveexample{The example below shows how array elements can be read and written using [] operator. Note the addition of null values.,operatorarray__size_type}
- Since
- version 1.0.0
◆ operator[]() [2/10]
|
inline |
access specified array element
Returns a const reference to the element at specified location idx.
- Parameters
-
[in] idx index of the element to access
- Returns
- const reference to the element at index idx
- Exceptions
-
std::domain_error if JSON is not an array; example: "cannot use operator[] with null"
@complexity Constant.
@liveexample{The example below shows how array elements can be read using the [] operator.,operatorarray__size_type_const}
- Since
- version 1.0.0
◆ operator[]() [3/10]
|
inline |
access specified object element
Returns a reference to the element at with specified key key.
- Note
- If key is not found in the object, then it is silently added to the object and filled with a
nullvalue to makekeya valid reference. In case the value wasnullbefore, it is converted to an object.
- Parameters
-
[in] key key of the element to access
- Returns
- reference to the element at key key
- Exceptions
-
std::domain_error if JSON is not an object or null; example: "cannot use operator[] with string"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- value() for access by value with a default value
- Since
- version 1.0.0
◆ operator[]() [4/10]
|
inline |
read-only access specified object element
Returns a const reference to the element at with specified key key. No bounds checking is performed.
- Warning
- If the element with key key does not exist, the behavior is undefined.
- Parameters
-
[in] key key of the element to access
- Returns
- const reference to the element at key key
- Precondition
- The element with key key must exist. This precondition is enforced with an assertion.
- Exceptions
-
std::domain_error if JSON is not an object; example: "cannot use operator[] with null"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read using the [] operator.,operatorarray__key_type_const}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- value() for access by value with a default value
- Since
- version 1.0.0
◆ operator[]() [5/10]
|
inline |
access specified object element
Returns a reference to the element at with specified key key.
- Note
- If key is not found in the object, then it is silently added to the object and filled with a
nullvalue to makekeya valid reference. In case the value wasnullbefore, it is converted to an object.
- Parameters
-
[in] key key of the element to access
- Returns
- reference to the element at key key
- Exceptions
-
std::domain_error if JSON is not an object or null; example: "cannot use operator[] with string"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- value() for access by value with a default value
- Since
- version 1.0.0
◆ operator[]() [6/10]
|
inline |
read-only access specified object element
Returns a const reference to the element at with specified key key. No bounds checking is performed.
- Warning
- If the element with key key does not exist, the behavior is undefined.
- Note
- This function is required for compatibility reasons with Clang.
- Parameters
-
[in] key key of the element to access
- Returns
- const reference to the element at key key
- Exceptions
-
std::domain_error if JSON is not an object; example: "cannot use operator[] with null"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read using the [] operator.,operatorarray__key_type_const}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- value() for access by value with a default value
- Since
- version 1.0.0
◆ operator[]() [7/10]
|
inline |
access specified object element
Returns a reference to the element at with specified key key.
- Note
- If key is not found in the object, then it is silently added to the object and filled with a
nullvalue to makekeya valid reference. In case the value wasnullbefore, it is converted to an object.
- Parameters
-
[in] key key of the element to access
- Returns
- reference to the element at key key
- Exceptions
-
std::domain_error if JSON is not an object or null; example: "cannot use operator[] with string"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read and written using the [] operator.,operatorarray__key_type}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- value() for access by value with a default value
- Since
- version 1.1.0
◆ operator[]() [8/10]
|
inline |
read-only access specified object element
Returns a const reference to the element at with specified key key. No bounds checking is performed.
- Warning
- If the element with key key does not exist, the behavior is undefined.
- Parameters
-
[in] key key of the element to access
- Returns
- const reference to the element at key key
- Precondition
- The element with key key must exist. This precondition is enforced with an assertion.
- Exceptions
-
std::domain_error if JSON is not an object; example: "cannot use operator[] with null"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be read using the [] operator.,operatorarray__key_type_const}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- value() for access by value with a default value
- Since
- version 1.1.0
◆ operator[]() [9/10]
|
inline |
access specified element via JSON Pointer
Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. Similar to operator[](const typename object_t::key_type&), null values are created in arrays and objects if necessary.
In particular:
- If the JSON pointer points to an object key that does not exist, it is created an filled with a
nullvalue before a reference to it is returned. - If the JSON pointer points to an array index that does not exist, it is created an filled with a
nullvalue before a reference to it is returned. All indices between the current maximum and the given index are also filled withnull. - The special value
-is treated as a synonym for the index past the end.
- Parameters
-
[in] ptr a JSON pointer
- Returns
- reference to the element pointed to by ptr
@complexity Constant.
- Exceptions
-
std::out_of_range if the JSON pointer can not be resolved std::domain_error if an array index begins with '0' std::invalid_argument if an array index was not a number
@liveexample{The behavior is shown in the example.,operatorjson_pointer}
- Since
- version 2.0.0
◆ operator[]() [10/10]
|
inline |
access specified element via JSON Pointer
Uses a JSON pointer to retrieve a reference to the respective JSON value. No bound checking is performed. The function does not change the JSON value; no null values are created. In particular, the the special value - yields an exception.
- Parameters
-
[in] ptr JSON pointer to the desired element
- Returns
- const reference to the element pointed to by ptr
@complexity Constant.
- Exceptions
-
std::out_of_range if the JSON pointer can not be resolved std::domain_error if an array index begins with '0' std::invalid_argument if an array index was not a number
@liveexample{The behavior is shown in the example.,operatorjson_pointer_const}
- Since
- version 2.0.0
◆ parse() [1/6]
|
inlinestatic |
deserialize from an array
This function reads from an array of 1-byte values.
- Precondition
- Each element of the container has a size of 1 byte. Violating this precondition yields undefined behavior. This precondition is enforced with a static assertion.
- Parameters
-
[in] array array to read from [in] cb a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
- Returns
- result of the deserialization
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
- Note
- A UTF-8 byte order mark is silently ignored.
@liveexample{The example below demonstrates the parse() function reading from an array.,parse__array__parser_callback_t}
- Since
- version 2.0.3
◆ parse() [2/6]
|
inlinestatic |
deserialize from string literal
- Template Parameters
-
CharT character/literal type with size of 1 byte
- Parameters
-
[in] s string literal to read a serialized JSON value from [in] cb a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
- Returns
- result of the deserialization
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
- Note
- A UTF-8 byte order mark is silently ignored.
-
String containers like
std::stringor string_t can be parsed with parse(const ContiguousContainer&, const parser_callback_t)
@liveexample{The example below demonstrates the parse() function with and without callback function.,parse__string__parser_callback_t}
- See also
- parse(std::istream&, const parser_callback_t) for a version that reads from an input stream
- Since
- version 1.0.0 (originally for string_t)
◆ parse() [3/6]
|
inlinestatic |
deserialize from stream
- Parameters
-
[in,out] i stream to read a serialized JSON value from [in] cb a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
- Returns
- result of the deserialization
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
- Note
- A UTF-8 byte order mark is silently ignored.
@liveexample{The example below demonstrates the parse() function with and without callback function.,parse__istream__parser_callback_t}
- See also
- parse(const CharT, const parser_callback_t) for a version that reads from a string
- Since
- version 1.0.0
◆ parse() [4/6]
|
inlinestatic |
deserialize from stream
- Parameters
-
[in,out] i stream to read a serialized JSON value from [in] cb a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
- Returns
- result of the deserialization
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
- Note
- A UTF-8 byte order mark is silently ignored.
@liveexample{The example below demonstrates the parse() function with and without callback function.,parse__istream__parser_callback_t}
- See also
- parse(const CharT, const parser_callback_t) for a version that reads from a string
- Since
- version 1.0.0
◆ parse() [5/6]
|
inlinestatic |
deserialize from an iterator range with contiguous storage
This function reads from an iterator range of a container with contiguous storage of 1-byte values. Compatible container types include std::vector, std::string, std::array, std::valarray, and std::initializer_list. Furthermore, C-style arrays can be used with std::begin()/std::end(). User-defined containers can be used as long as they implement random-access iterators and a contiguous storage.
- Precondition
- The iterator range is contiguous. Violating this precondition yields undefined behavior. This precondition is enforced with an assertion.
- Each element in the range has a size of 1 byte. Violating this precondition yields undefined behavior. This precondition is enforced with a static assertion.
- Warning
- There is no way to enforce all preconditions at compile-time. If the function is called with noncompliant iterators and with assertions switched off, the behavior is undefined and will most likely yield segmentation violation.
- Template Parameters
-
IteratorType iterator of container with contiguous storage
- Parameters
-
[in] first begin of the range to parse (included) [in] last end of the range to parse (excluded) [in] cb a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
- Returns
- result of the deserialization
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
- Note
- A UTF-8 byte order mark is silently ignored.
@liveexample{The example below demonstrates the parse() function reading from an iterator range.,parse__iteratortype__parser_callback_t}
- Since
- version 2.0.3
◆ parse() [6/6]
|
inlinestatic |
deserialize from a container with contiguous storage
This function reads from a container with contiguous storage of 1-byte values. Compatible container types include std::vector, std::string, std::array, and std::initializer_list. User-defined containers can be used as long as they implement random-access iterators and a contiguous storage.
- Precondition
- The container storage is contiguous. Violating this precondition yields undefined behavior. This precondition is enforced with an assertion.
- Each element of the container has a size of 1 byte. Violating this precondition yields undefined behavior. This precondition is enforced with a static assertion.
- Warning
- There is no way to enforce all preconditions at compile-time. If the function is called with a noncompliant container and with assertions switched off, the behavior is undefined and will most likely yield segmentation violation.
- Template Parameters
-
ContiguousContainer container type with contiguous storage
- Parameters
-
[in] c container to read from [in] cb a parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
- Returns
- result of the deserialization
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
- Note
- A UTF-8 byte order mark is silently ignored.
@liveexample{The example below demonstrates the parse() function reading from a contiguous container.,parse__contiguouscontainer__parser_callback_t}
- Since
- version 2.0.3
◆ patch()
|
inline |
applies a JSON patch
JSON Patch defines a JSON document structure for expressing a sequence of operations to apply to a JSON) document. With this function, a JSON Patch is applied to the current JSON value by executing all operations from the patch.
- Parameters
-
[in] json_patch JSON patch document
- Returns
- patched document
- Note
- The application of a patch is atomic: Either all operations succeed and the patched document is returned or an exception is thrown. In any case, the original value is not changed: the patch is applied to a copy of the value.
- Exceptions
-
std::out_of_range if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example: "key baz not found"invalid_argument if the JSON patch is malformed (e.g., mandatory attributes are missing); example: "operation add must have member path"
@complexity Linear in the size of the JSON value and the length of the JSON patch. As usually only a fraction of the JSON value is affected by the patch, the complexity can usually be neglected.
@liveexample{The following code shows how a JSON patch is applied to a value.,patch}
- See also
- diff – create a JSON patch by comparing two JSON values
- RFC 6902 (JSON Patch)
- RFC 6901 (JSON Pointer)
- Since
- version 2.0.0
◆ push_back() [1/4]
|
inline |
add an object to an array
Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.
- Parameters
-
[in] val the value to add to the JSON array
- Exceptions
-
std::domain_error when called on a type other than JSON array or null; example: "cannot use push_back() with number"
@complexity Amortized constant.
@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}
- Since
- version 1.0.0
◆ push_back() [2/4]
|
inline |
add an object to an array
add an object to an array Appends the given element val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending val.
- Parameters
-
[in] val the value to add to the JSON array
- Exceptions
-
std::domain_error when called on a type other than JSON array or null; example: "cannot use push_back() with number"
@complexity Amortized constant.
@liveexample{The example shows how push_back() and += can be used to add elements to a JSON array. Note how the null value was silently converted to a JSON array.,push_back}
- Since
- version 1.0.0
◆ push_back() [3/4]
|
inline |
add an object to an object
Inserts the given element val to the JSON object. If the function is called on a JSON null value, an empty object is created before inserting val.
- Parameters
-
[in] val the value to add to the JSON object
- Exceptions
-
std::domain_error when called on a type other than JSON object or null; example: "cannot use push_back() with number"
@complexity Logarithmic in the size of the container, O(log(size())).
@liveexample{The example shows how push_back() and += can be used to add elements to a JSON object. Note how the null value was silently converted to a JSON object.,push_back__object_t__value}
- Since
- version 1.0.0
◆ push_back() [4/4]
|
inline |
add an object to an object
This function allows to use push_back with an initializer list. In case
- the current value is an object,
- the initializer list init contains only two elements, and
- the first element of init is a string,
init is converted into an object element and added using push_back(const typename object_t::value_type&). Otherwise, init is converted to a JSON value and added using push_back(basic_json&&).
- Parameters
-
init an initializer list
@complexity Linear in the size of the initializer list init.
- Note
- This function is required to resolve an ambiguous overload error, because pairs like
{"key", "value"}can be both interpreted asobject_t::value_typeorstd::initializer_list<basic_json>, see https://github.com/nlohmann/json/issues/235 for more information.
@liveexample{The example shows how initializer lists are treated as objects when possible.,push_back__initializer_list}
◆ rbegin() [1/2]
|
inlinenoexcept |
returns an iterator to the reverse-beginning
Returns an iterator to the reverse-beginning; that is, the last element.
@complexity Constant.
@requirement This function helps basic_json satisfying the ReversibleContainer requirements:
- The complexity is constant.
- Has the semantics of
reverse_iterator(end()).
@liveexample{The following code shows an example for rbegin().,rbegin}
- See also
- crbegin() – returns a const reverse iterator to the beginning
- rend() – returns a reverse iterator to the end
- crend() – returns a const reverse iterator to the end
- Since
- version 1.0.0
◆ rbegin() [2/2]
|
inlinenoexcept |
returns a const reverse iterator to the last element
Returns a const iterator to the reverse-beginning; that is, the last element.
@complexity Constant.
@requirement This function helps basic_json satisfying the ReversibleContainer requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).rbegin().
@liveexample{The following code shows an example for crbegin().,crbegin}
- See also
- rbegin() – returns a reverse iterator to the beginning
- rend() – returns a reverse iterator to the end
- crend() – returns a const reverse iterator to the end
- Since
- version 1.0.0
◆ rend() [1/2]
|
inlinenoexcept |
returns an iterator to the reverse-end
Returns an iterator to the reverse-end; that is, one before the first element.
@complexity Constant.
@requirement This function helps basic_json satisfying the ReversibleContainer requirements:
- The complexity is constant.
- Has the semantics of
reverse_iterator(begin()).
@liveexample{The following code shows an example for rend().,rend}
- See also
- crend() – returns a const reverse iterator to the end
- rbegin() – returns a reverse iterator to the beginning
- crbegin() – returns a const reverse iterator to the beginning
- Since
- version 1.0.0
◆ rend() [2/2]
|
inlinenoexcept |
returns a const reverse iterator to one before the first
Returns a const reverse iterator to the reverse-end; that is, one before the first element.
@complexity Constant.
@requirement This function helps basic_json satisfying the ReversibleContainer requirements:
- The complexity is constant.
- Has the semantics of
const_cast<const basic_json&>(*this).rend().
@liveexample{The following code shows an example for crend().,crend}
- See also
- rend() – returns a reverse iterator to the end
- rbegin() – returns a reverse iterator to the beginning
- crbegin() – returns a const reverse iterator to the beginning
- Since
- version 1.0.0
◆ size()
|
inlinenoexcept |
returns the number of elements
Returns the number of elements in a JSON value.
- Returns
- The return value depends on the different types and is defined as follows:
Value type return value null 0boolean 1string 1number 1object result of function object_t::size() array result of function array_t::size()
- Note
- This function does not return the length of a string stored as JSON value - it returns the number of elements in the JSON value which is 1 in the case of a string.
@complexity Constant, as long as array_t and object_t satisfy the Container concept; that is, their size() functions have constant complexity.
@requirement This function helps basic_json satisfying the Container requirements:
@liveexample{The following code calls size() on the different value types.,size}
- See also
- empty() – checks whether the container is empty
- max_size() – returns the maximal number of elements
- Since
- version 1.0.0
◆ swap() [1/4]
|
inlinenoexcept |
exchanges the values
Exchanges the contents of the JSON value with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
- Parameters
-
[in,out] other JSON value to exchange the contents with
@complexity Constant.
@liveexample{The example below shows how JSON values can be swapped with swap().,swap__reference}
- Since
- version 1.0.0
◆ swap() [2/4]
|
inline |
exchanges the values
Exchanges the contents of a JSON array with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
- Parameters
-
[in,out] other array to exchange the contents with
- Exceptions
-
std::domain_error when JSON value is not an array; example: "cannot use swap() with string"
@complexity Constant.
@liveexample{The example below shows how arrays can be swapped with swap().,swap__array_t}
- Since
- version 1.0.0
◆ swap() [3/4]
|
inline |
exchanges the values
Exchanges the contents of a JSON object with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
- Parameters
-
[in,out] other object to exchange the contents with
- Exceptions
-
std::domain_error when JSON value is not an object; example: "cannot use swap() with string"
@complexity Constant.
@liveexample{The example below shows how objects can be swapped with swap().,swap__object_t}
- Since
- version 1.0.0
◆ swap() [4/4]
|
inline |
exchanges the values
Exchanges the contents of a JSON string with those of other. Does not invoke any move, copy, or swap operations on individual elements. All iterators and references remain valid. The past-the-end iterator is invalidated.
- Parameters
-
[in,out] other string to exchange the contents with
- Exceptions
-
std::domain_error when JSON value is not a string; example: "cannot use swap() with boolean"
@complexity Constant.
@liveexample{The example below shows how strings can be swapped with swap().,swap__string_t}
- Since
- version 1.0.0
◆ to_cbor()
|
inlinestatic |
create a MessagePack serialization of a given JSON value
Serializes a given JSON value j to a byte vector using the CBOR (Concise Binary Object Representation) serialization format. CBOR is a binary serialization format which aims to be more compact than JSON itself, yet more efficient to parse.
- Parameters
-
[in] j JSON value to serialize
- Returns
- MessagePack serialization as byte vector
@complexity Linear in the size of the JSON value j.
@liveexample{The example shows the serialization of a JSON value to a byte vector in CBOR format.,to_cbor}
- See also
- http://cbor.io
- from_cbor(const std::vector<uint8_t>&, const size_t) for the analogous deserialization
- to_msgpack(const basic_json& for the related MessagePack format
- Since
- version 2.0.9
◆ to_msgpack()
|
inlinestatic |
create a MessagePack serialization of a given JSON value
Serializes a given JSON value j to a byte vector using the MessagePack serialization format. MessagePack is a binary serialization format which aims to be more compact than JSON itself, yet more efficient to parse.
- Parameters
-
[in] j JSON value to serialize
- Returns
- MessagePack serialization as byte vector
@complexity Linear in the size of the JSON value j.
@liveexample{The example shows the serialization of a JSON value to a byte vector in MessagePack format.,to_msgpack}
- See also
- http://msgpack.org
- from_msgpack(const std::vector<uint8_t>&, const size_t) for the analogous deserialization
- to_cbor(const basic_json& for the related CBOR format
- Since
- version 2.0.9
◆ type()
|
inlinenoexcept |
return the type of the JSON value (explicit)
Return the type of the JSON value as a value from the value_t enumeration.
- Returns
- the type of the JSON value
@complexity Constant.
@exceptionsafety No-throw guarantee: this member function never throws exceptions.
@liveexample{The following code exemplifies type() for all JSON types.,type}
- Since
- version 1.0.0
◆ type_name()
|
inline |
return the type as string
Returns the type name as string to be used in error messages - usually to indicate that a function was called on a wrong JSON type.
- Returns
- basically a string representation of a the m_type member
@complexity Constant.
@liveexample{The following code exemplifies type_name() for all JSON types.,type_name}
- Since
- version 1.0.0, public since 2.1.0
◆ unflatten()
|
inline |
unflatten a previously flattened JSON value
The function restores the arbitrary nesting of a JSON value that has been flattened before using the flatten() function. The JSON value must meet certain constraints:
- The value must be an object.
- The keys must be JSON pointers (see RFC 6901)
- The mapped values must be primitive JSON types.
- Returns
- the original JSON from a flattened version
- Note
- Empty objects and arrays are flattened by flatten() to
nullvalues and can not unflattened to their original type. Apart from this example, for a JSON valuej, the following is always true:j == j.flatten().unflatten().
@complexity Linear in the size the JSON value.
@liveexample{The following code shows how a flattened JSON object is unflattened into the original nested JSON object.,unflatten}
- See also
- flatten() for the reverse function
- Since
- version 2.0.0
◆ value() [1/4]
|
inline |
access specified object element with default value
Returns either a copy of an object's element at the specified key key or a given default value if no element with key key exists.
The function is basically equivalent to executing
- Note
- Unlike at(const typename object_t::key_type&), this function does not throw if the given key key was not found.
- Unlike operator[](const typename object_t::key_type& key), this function does not implicitly add an element to the position defined by key. This function is furthermore also applicable to const objects.
- Parameters
-
[in] key key of the element to access [in] default_value the value to return if key is not found
- Template Parameters
-
ValueType type compatible to JSON values, for instance intfor JSON integer numbers,boolfor JSON booleans, orstd::vectortypes for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.
- Returns
- copy of the element at key key or default_value if key is not found
- Exceptions
-
std::domain_error if JSON is not an object; example: "cannot use value() with null"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- operator[](const typename object_t::key_type&) for unchecked access by reference
- Since
- version 1.0.0
◆ value() [2/4]
|
inline |
overload for a default value of type const char*
access specified object element with default value Returns either a copy of an object's element at the specified key key or a given default value if no element with key key exists.
The function is basically equivalent to executing
- Note
- Unlike at(const typename object_t::key_type&), this function does not throw if the given key key was not found.
- Unlike operator[](const typename object_t::key_type& key), this function does not implicitly add an element to the position defined by key. This function is furthermore also applicable to const objects.
- Parameters
-
[in] key key of the element to access [in] default_value the value to return if key is not found
- Template Parameters
-
ValueType type compatible to JSON values, for instance intfor JSON integer numbers,boolfor JSON booleans, orstd::vectortypes for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.
- Returns
- copy of the element at key key or default_value if key is not found
- Exceptions
-
std::domain_error if JSON is not an object; example: "cannot use value() with null"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value}
- See also
- at(const typename object_t::key_type&) for access by reference with range checking
- operator[](const typename object_t::key_type&) for unchecked access by reference
- Since
- version 1.0.0
◆ value() [3/4]
|
inline |
access specified object element via JSON Pointer with default value
Returns either a copy of an object's element at the specified key key or a given default value if no element with key key exists.
The function is basically equivalent to executing
- Note
- Unlike at(const json_pointer&), this function does not throw if the given key key was not found.
- Parameters
-
[in] ptr a JSON pointer to the element to access [in] default_value the value to return if ptr found no value
- Template Parameters
-
ValueType type compatible to JSON values, for instance intfor JSON integer numbers,boolfor JSON booleans, orstd::vectortypes for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.
- Returns
- copy of the element at key key or default_value if key is not found
- Exceptions
-
std::domain_error if JSON is not an object; example: "cannot use value() with null"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value_ptr}
- See also
- operator[](const json_pointer&) for unchecked access by reference
- Since
- version 2.0.2
◆ value() [4/4]
|
inline |
overload for a default value of type const char*
access specified object element via JSON Pointer with default value Returns either a copy of an object's element at the specified key key or a given default value if no element with key key exists.
The function is basically equivalent to executing
- Note
- Unlike at(const json_pointer&), this function does not throw if the given key key was not found.
- Parameters
-
[in] ptr a JSON pointer to the element to access [in] default_value the value to return if ptr found no value
- Template Parameters
-
ValueType type compatible to JSON values, for instance intfor JSON integer numbers,boolfor JSON booleans, orstd::vectortypes for JSON arrays. Note the type of the expected value at key and the default value default_value must be compatible.
- Returns
- copy of the element at key key or default_value if key is not found
- Exceptions
-
std::domain_error if JSON is not an object; example: "cannot use value() with null"
@complexity Logarithmic in the size of the container.
@liveexample{The example below shows how object elements can be queried with a default value.,basic_json__value_ptr}
- See also
- operator[](const json_pointer&) for unchecked access by reference
- Since
- version 2.0.2
Friends And Related Function Documentation
◆ detail::external_constructor
|
friend |
◆ operator!= [1/3]
|
friend |
comparison: not equal
Compares two JSON values for inequality by calculating not (lhs == rhs).
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether the values lhs and rhs are not equal
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}
- Since
- version 1.0.0
◆ operator!= [2/3]
|
friend |
comparison: not equal
comparison: not equal Compares two JSON values for inequality by calculating not (lhs == rhs).
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether the values lhs and rhs are not equal
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}
- Since
- version 1.0.0
◆ operator!= [3/3]
|
friend |
comparison: not equal
comparison: not equal Compares two JSON values for inequality by calculating not (lhs == rhs).
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether the values lhs and rhs are not equal
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__notequal}
- Since
- version 1.0.0
◆ operator<
|
friend |
comparison: less than
Compares whether one JSON value lhs is less than another JSON value rhs according to the following rules:
- If lhs and rhs have the same type, the values are compared using the default
<operator. - Integer and floating-point numbers are automatically converted before comparison
- In case lhs and rhs have different types, the values are ignored and the order of the types is considered, see operator<(const value_t, const value_t).
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether lhs is less than rhs
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__less}
- Since
- version 1.0.0
◆ operator<< [1/2]
|
friend |
serialize to stream
Serialize the given JSON value j to the output stream o. The JSON value will be serialized using the dump member function. The indentation of the output can be controlled with the member variable width of the output stream o. For instance, using the manipulator std::setw(4) on o sets the indentation level to 4 and the serialization result is the same as calling dump(4).
- Parameters
-
[in,out] o stream to serialize to [in] j JSON value to serialize
- Returns
- the stream o
@complexity Linear.
@liveexample{The example below shows the serialization with different parameters to width to adjust the indentation level.,operator_serialize}
- Since
- version 1.0.0
◆ operator<< [2/2]
|
friend |
deserialize from stream
Deserializes an input stream to a JSON value.
- Parameters
-
[in,out] i input stream to read a serialized JSON value from [in,out] j JSON value to write the deserialized input to
- Exceptions
-
std::invalid_argument in case of parse errors
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser.
- Note
- A UTF-8 byte order mark is silently ignored.
@liveexample{The example below shows how a JSON value is constructed by reading a serialization from a stream.,operator_deserialize}
- See also
- parse(std::istream&, const parser_callback_t) for a variant with a parser callback function to filter values while parsing
- Since
- version 1.0.0
◆ operator<=
|
friend |
comparison: less than or equal
Compares whether one JSON value lhs is less than or equal to another JSON value by calculating not (rhs < lhs).
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether lhs is less than or equal to rhs
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__greater}
- Since
- version 1.0.0
◆ operator== [1/3]
|
friend |
comparison: equal
Compares two JSON values for equality according to the following rules:
- Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same.
- Integer and floating-point numbers are automatically converted before comparison. Floating-point numbers are compared indirectly: two floating-point numbers
f1andf2are considered equal if neitherf1 > f2norf2 > f1holds. - Two JSON null values are equal.
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether the values lhs and rhs are equal
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__equal}
- Since
- version 1.0.0
◆ operator== [2/3]
|
friend |
comparison: equal
comparison: equal Compares two JSON values for equality according to the following rules:
- Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same.
- Integer and floating-point numbers are automatically converted before comparison. Floating-point numbers are compared indirectly: two floating-point numbers
f1andf2are considered equal if neitherf1 > f2norf2 > f1holds. - Two JSON null values are equal.
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether the values lhs and rhs are equal
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__equal}
- Since
- version 1.0.0
◆ operator== [3/3]
|
friend |
comparison: equal
comparison: equal Compares two JSON values for equality according to the following rules:
- Two JSON values are equal if (1) they are from the same type and (2) their stored values are the same.
- Integer and floating-point numbers are automatically converted before comparison. Floating-point numbers are compared indirectly: two floating-point numbers
f1andf2are considered equal if neitherf1 > f2norf2 > f1holds. - Two JSON null values are equal.
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether the values lhs and rhs are equal
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__equal}
- Since
- version 1.0.0
◆ operator>
|
friend |
comparison: greater than
Compares whether one JSON value lhs is greater than another JSON value by calculating not (lhs <= rhs).
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether lhs is greater than to rhs
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__lessequal}
- Since
- version 1.0.0
◆ operator>=
|
friend |
comparison: greater than or equal
Compares whether one JSON value lhs is greater than or equal to another JSON value by calculating not (lhs < rhs).
- Parameters
-
[in] lhs first JSON value to consider [in] rhs second JSON value to consider
- Returns
- whether lhs is greater than or equal to rhs
@complexity Linear.
@liveexample{The example demonstrates comparing several JSON types.,operator__greaterequal}
- Since
- version 1.0.0
◆ operator>> [1/2]
|
friend |
serialize to stream
serialize to stream Serialize the given JSON value j to the output stream o. The JSON value will be serialized using the dump member function. The indentation of the output can be controlled with the member variable width of the output stream o. For instance, using the manipulator std::setw(4) on o sets the indentation level to 4 and the serialization result is the same as calling dump(4).
- Parameters
-
[in,out] o stream to serialize to [in] j JSON value to serialize
- Returns
- the stream o
@complexity Linear.
@liveexample{The example below shows the serialization with different parameters to width to adjust the indentation level.,operator_serialize}
- Since
- version 1.0.0
◆ operator>> [2/2]
|
friend |
deserialize from stream
deserialize from stream Deserializes an input stream to a JSON value.
- Parameters
-
[in,out] i input stream to read a serialized JSON value from [in,out] j JSON value to write the deserialized input to
- Exceptions
-
std::invalid_argument in case of parse errors
@complexity Linear in the length of the input. The parser is a predictive LL(1) parser.
- Note
- A UTF-8 byte order mark is silently ignored.
@liveexample{The example below shows how a JSON value is constructed by reading a serialization from a stream.,operator_deserialize}
- See also
- parse(std::istream&, const parser_callback_t) for a variant with a parser callback function to filter values while parsing
- Since
- version 1.0.0
The documentation for this class was generated from the following file:
- GLAC/lib/json.hpp
