typedef basic_json<char,
ImplementationPolicy = sorted_policy,
Allocator = std::allocator<char>> jsonThe class json is an instantiation of the basic_json class template that uses char as the character type. The order of an object's name/value pairs is not preserved, they are sorted alphabetically by name. If you want to preserve the original insertion order, use ojson instead.
The class json resembles a union. An instance of json holds a data item of one of its alternative types:
- null
- bool
- int64
- uint64
- double
- string
- byte string
- array
- object
The data item may be tagged with a semantic_tag that provides additional information about the data item.
When assigned a new value, the old value is overwritten. The type of the new value may be different from the old value.
The jsoncons library will rebind the supplied allocator from the template parameter to internal data structures.
#include <jsoncons/json.hpp>| Member type | Definition |
|---|---|
json_type |
json |
reference |
json& |
const_reference |
const json& |
pointer |
json* |
const_pointer |
const json* |
allocator_type |
Allocator type |
char_allocator |
String allocator type |
array_allocator |
Array allocator type |
object_allocator |
Object allocator |
string_view_type |
A non-owning view of a string, holds a pointer to character data and length. Supports conversion to and from strings. Will be typedefed to the C++ 17 string view if JSONCONS_HAS_STRING_VIEW is defined in jsoncons_config.hpp, otherwise proxied. |
key_value_type |
key_value_type is a class that stores a name and a json value |
object |
json object type |
array |
json array type |
object_iterator |
A RandomAccessIterator to key_value_type |
const_object_iterator |
A const RandomAccessIterator to const key_value_type |
array_iterator |
A RandomAccessIterator to json |
const_array_iterator |
A const RandomAccessIterator to const json |
| parse | Parses JSON. |
| make_array | Makes a multidimensional json array. |
| const json& null() | Returns a null value |
| (constructor) | constructs the json value |
| (destructor) | destructs the json value |
| operator= | assigns values |
allocator_type get_allocator() const
Returns the allocator associated with the json value.
| array_range | Returns a "range" that supports a range-based for loop over the elements of a `json` array. |
| obect_range | Returns a "range" that supports a range-based for loop over the key-value pairs of a `json` object. |
| size_t size() const noexcept | Returns the number of elements in a json array, or the number of members in a json object, or `zero` |
| bool empty() const noexcept | Returns true if a json string, object or array has no elements, otherwise false |
| size_t capacity() const | Returns the size of the storage space currently allocated for a json object or array |
| void reserve(size_t n) | Increases the capacity of a json object or array to allow at least `n` members or elements |
| void resize(size_t n) | Resizes a json array so that it contains `n` elements |
| void resize(size_t n, const json& val) | Resizes a json array so that it contains `n` elements that are initialized to `val` |
| void shrink_to_fit() | Requests the removal of unused capacity |
bool contains(const string_view_type& key) const |
Returns true if an object has a member with the given `key`, otherwise false |
bool count(const string_view_type& key) const |
Returns the number of object members that match `key` |
| is | Checks if a json value matches a type. |
| as | Attempts to convert a json value to a value of a type. |
semantic_tag get_semantic_tag() const
Returns the semantic_tag associated with this value
json& operator[](size_t i)
const json& operator[](size_t i) const
Returns a reference to the value at position i in a json object or array.
Throws std::runtime_error if not an object or array.
json& operator[](const string_view_type& name)
Returns a proxy to a keyed value. If written to, inserts or updates with the new value. If read, evaluates to a reference to the keyed value, if it exists, otherwise throws.
Throws std::runtime_error if not an object.
If read, throws std::out_of_range if the object does not have a member with the specified name.
const json& operator[](const string_view_type& name) const
If name matches the name of a member in the json object, returns a reference to the json object, otherwise throws.
Throws std::runtime_error if not an object.
Throws std::out_of_range if the object does not have a member with the specified name.
object_iterator find(const string_view_type& name)
const_object_iterator find(const string_view_type& name) const
Returns an object iterator to a member whose name compares equal to name. If there is no such member, returns end_member().
Throws std::runtime_error if not an object.
json& at(const string_view_type& name)
const json& at(const string_view_type& name) const
Returns a reference to the value with the specifed name in a json object.
Throws std::runtime_error if not an object.
Throws std::out_of_range if the object does not have a member with the specified name.
json& at(size_t i)
const json& at(size_t i) const
Returns a reference to the element at index i in a json array.
Throws std::runtime_error if not an array.
Throws std::out_of_range if the index is outside the bounds of the array.
template <class T>
T get_with_default(const string_view_type& name,
const T& default_val) const
If name matches the name of a member in the json object, returns the member value converted to the default's data type, otherwise returns default_val.
Throws std::runtime_error if not an object.
template <class T = std::string>
T get_with_default(const string_view_type& name,
const char_type* default_val) const
Make get_with_default do the right thing for string literals.
Throws std::runtime_error if not an object.
| void clear() | Remove all elements from an array or members from an object, otherwise do nothing |
| erase | Erases array elements and object members |
| push_back | Adds a value to the end of a json array |
| insert | Inserts elements |
| emplace_back | Constructs a value in place at the end of a json array |
| emplace | Constructs a value in place before a specified position in a json array |
| try_emplace | Constructs a key-value pair in place in a json object if the key does not exist, does nothing if the key exists |
| insert_or_assign | Inserts a key-value pair in a json object if the key does not exist, or assigns a new value if the key already exists |
| merge | Inserts another json object's key-value pairs into a json object, if they don't already exist. |
| merge_or_update | Inserts another json object's key-value pairs into a json object, or assigns them if they already exist. |
| void swap(json& val) | Exchanges the content of the json value with the content of val, which is another json value |
| dump | Serializes json value to a string, stream, or output handler. |
bool operator==(const json& lhs, const json& rhs) |
Returns true if two json objects compare equal, |
bool operator!=(const json& lhs, const json& rhs) |
Returns true if two json objects do not compare equal, |
bool operator<(const json& lhs, const json& rhs) |
Compares the contents of lhs and rhs lexicographically. |
bool operator<=(const json& lhs, const json& rhs) |
Compares the contents of lhs and rhs lexicographically. |
bool operator>(const json& lhs, const json& rhs) |
Compares the contents of lhs and rhs lexicographically. |
bool operator>=(const json& lhs, const json& rhs) |
Compares the contents of lhs and rhs lexicographically. |
std::istream& operator>> (std::istream& os, json& val)
Reads a json value from a stream.
std::ostream& operator<< (std::ostream& os, const json& val)
Inserts json value into stream.
std::ostream& print(const json& val)
std::ostream& print(const json& val, const json_options<CharT>& options)
Inserts json value into stream using the specified json_options if supplied.
std::ostream& pretty_print(const json& val)
std::ostream& pretty_print(const json& val, const json_options<CharT>& options)
Inserts json value into stream using the specified json_options if supplied.
void swap(json& a, json& b)
Exchanges the values of a and b
As the jsoncons library has evolved, names have sometimes changed. To ease transition, jsoncons deprecates the old names but continues to support many of them. See the deprecated list for the status of old names. The deprecated names can be suppressed by defining macro JSONCONS_NO_DEPRECATED, which is recommended for new code.
-
ojson constructs a json value that preserves the original name-value insertion order
-
wjson constructs a wide character json value that sorts name-value members alphabetically
-
wojson constructs a wide character json value that preserves the original name-value insertion order
json val;
val["field1"] = 1;
val["field3"] = "Toronto";
double x1 = obj.contains("field1") ? val["field1"].as<double>() : 10.0;
double x2 = obj.contains("field2") ? val["field2"].as<double>() : 20.0;
std::string x3 = obj.get_with_default("field3","Montreal");
std::string x4 = obj.get_with_default("field4","San Francisco");
std::cout << "x1=" << x1 << '\n';
std::cout << "x2=" << x2 << '\n';
std::cout << "x3=" << x3 << '\n';
std::cout << "x4=" << x4 << '\n';Output:
x1=1
x2=20
x3=Toronto
x4=San Franciscojson obj;
obj["field1"] = json::null();
std::cout << obj << std::endl;Output:
{"field1":null}json root;
root["persons"] = json::array();
json person;
person["first_name"] = "John";
person["last_name"] = "Smith";
person["birth_date"] = "1972-01-30";
json address;
address["city"] = "Toronto";
address["country"] = "Canada";
person["address"] = std::move(address);
root["persons"].push_back(std::move(person));
std::cout << pretty_print(root) << std::endl;Output:
{
"persons":
[
{
"address":
{
"city":"Toronto",
"country":"Canada"
},
"birth_date":"1972-01-30",
"first_name":"John",
"last_name":"Smith"
}
]
}