JSON for Modern C++  3.7.0

◆ basic_json() [1/9]

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>
nlohmann::basic_json::basic_json ( const value_t  v)
inline

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]vthe type of the value to create
Complexity
Constant.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes to any JSON value.
Example
The following code shows the constructor for different value_t values
1 #include <iostream>
2 #include <nlohmann/json.hpp>
3 
4 using json = nlohmann::json;
5 
6 int main()
7 {
8  // create the different JSON values with default values
9  json j_null(json::value_t::null);
10  json j_boolean(json::value_t::boolean);
11  json j_number_integer(json::value_t::number_integer);
12  json j_number_float(json::value_t::number_float);
13  json j_object(json::value_t::object);
14  json j_array(json::value_t::array);
15  json j_string(json::value_t::string);
16 
17  // serialize the JSON values
18  std::cout << j_null << '\n';
19  std::cout << j_boolean << '\n';
20  std::cout << j_number_integer << '\n';
21  std::cout << j_number_float << '\n';
22  std::cout << j_object << '\n';
23  std::cout << j_array << '\n';
24  std::cout << j_string << '\n';
25 }
basic_json<> json
default JSON class
Definition: json.hpp:2355

Output (play with this example online):
null
false
0
0.0
{}
[]
""
The example code above can be translated with
g++ -std=c++11 -Isingle_include doc/examples/basic_json__value_t.cpp -o basic_json__value_t 
See also
clear() – restores the postcondition of this constructor
Since
version 1.0.0

Definition at line 15568 of file json.hpp.