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json operator "" _json(const char* s, std::size_t n);

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.


s (in)
a string representation of a JSON object
n (in)
length of string s

Return value

json value parsed from s


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





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';


  "answer": 42,
  "hello": "world"

Version history

  • Added in version 1.0.0.
  • Moved to namespace nlohmann::literals::json_literals in 3.11.0.

Last update: October 2, 2022