nlohmann::operator""_json

json operator ""_json(const char* s, std::size_t n);
json operator ""_json(const char8_t* s, std::size_t n);  // since C++20

This operator implements a user-defined string literal for JSON objects. It can be used by adding _json to a string literal and returns a json object if no parse error occurred.

It is recommended to bring the operator into scope using any of the following lines:

using nlohmann::literals::operator ""_json;
using namespace nlohmann::literals;
using namespace nlohmann::json_literals;
using namespace nlohmann::literals::json_literals;
using namespace nlohmann;

This is suggested to ease migration to the next major version release of the library. See JSON_USE_GLOBAL_UDLS for details.

Parameters

s (in) : a string representation of a JSON object

n (in) : length of string s

Return value

json value parsed from s

Exceptions

The function can throw anything that parse(s, s+n) would throw.

Complexity

Linear.

Examples

Example

The following code shows how to create JSON values from string literals.

#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>

using json = nlohmann::json;
using namespace nlohmann::literals;

int main()
{
    json j = R"( {"hello": "world", "answer": 42} )"_json;

    std::cout << std::setw(2) << j << '\n';
}

Output:

{
  "answer": 42,
  "hello": "world"
}

See also

• Creating JSON values - the article on creating JSON values

Version history

• Added in version 1.0.0.
• Moved to namespace nlohmann::literals::json_literals in 3.11.0.
• Added char8_t* overload in 3.13.0.