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 = int64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator>

nlohmann::basic_json::basic_json ( const value_t  value )

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]

value

the type of the value to create

Complexity

Constant.

Exceptions

std::bad_alloc

if allocation for object, array, or string value fails (thrown by the constructors of json_value)

Example

The following code shows the constructor for different value_t values

#include <json.hpp>

using namespace nlohmann;

int main()
{
    // create the different JSON values with default values
    json j_null(json::value_t::null);
    json j_boolean(json::value_t::boolean);
    json j_number_integer(json::value_t::number_integer);
    json j_number_float(json::value_t::number_float);
    json j_object(json::value_t::object);
    json j_array(json::value_t::array);
    json j_string(json::value_t::string);

    // serialize the JSON values
    std::cout << j_null << '\n';
    std::cout << j_boolean << '\n';
    std::cout << j_number_integer << '\n';
    std::cout << j_number_float << '\n';
    std::cout << j_object << '\n';
    std::cout << j_array << '\n';
    std::cout << j_string << '\n';
}

Output:

null
false
0
0
{}
[]
""

The example code above can be translated with

g++ -std=c++11 -Isrc doc/examples/basic_json__value_t.cpp -o basic_json__value_t 

.