nlohmann::operator<<(basic_json), nlohmann::operator<<(json_pointer)¶

std::ostream& operator<<(std::ostream& o, const basic_json& j);      // (1)

std::ostream& operator<<(std::ostream& o, const json_pointer& ptr);  // (2)

1. Serialize the given JSON value j to the output stream o. The JSON value will be serialized using the dump member function.
   • The indentation of the output can be controlled with the member variable width of the output stream o. For instance, using the manipulator std::setw(4) on o sets the indentation level to 4 and the serialization result is the same as calling dump(4).
   • The indentation character can be controlled with the member variable fill of the output stream o. For instance, the manipulator std::setfill('\\t') sets indentation to use a tab character rather than the default space character.
2. Write a string representation of the given JSON pointer ptr to the output stream o. The string representation is obtained using the to_string member function.

Parameters¶

o (in, out)

stream to write to

j (in)

JSON value to serialize

ptr (in)

JSON pointer to write

Return value¶

the stream o

Exceptions¶

1. Throws type_error.316 if a string stored inside the JSON value is not UTF-8 encoded. Note that unlike the dump member functions, no error_handler can be set.
2. None.

Complexity¶

Linear.

Notes¶

Examples¶

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

using json = nlohmann::json;

int main()
{
    // create JSON values
    json j_object = {{"one", 1}, {"two", 2}};
    json j_array = {1, 2, 4, 8, 16};

    // serialize without indentation
    std::cout << j_object << "\n\n";
    std::cout << j_array << "\n\n";

    // serialize with indentation
    std::cout << std::setw(4) << j_object << "\n\n";
    std::cout << std::setw(2) << j_array << "\n\n";
    std::cout << std::setw(1) << std::setfill('\t') << j_object << "\n\n";
}

{"one":1,"two":2}

[1,2,4,8,16]

{
    "one": 1,
    "two": 2
}

[
  1,
  2,
  4,
  8,
  16
]

{
    "one": 1,
    "two": 2
}

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

using json = nlohmann::json;

int main()
{
    // create JSON poiner
    json::json_pointer ptr("/foo/bar/baz");

    // write string representation to stream
    std::cout << ptr << std::endl;
}

/foo/bar/baz

Version history¶

1. Added in version 1.0.0. Added support for indentation character and deprecated std::ostream& operator>>(const basic_json& j, std::ostream& o) in version 3.0.0.
2. Added in version 3.11.0.