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# 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

Deprecation

Function `std::ostream& operator<<(std::ostream& o, const basic_json& j)` replaces function `std::ostream& operator>>(const basic_json& j, std::ostream& o)` which has been deprecated in version 3.0.0. It will be removed in version 4.0.0. Please replace calls like `j >> o;` with `o << j;`.

## Examples

Example: (1) serialize JSON value to stream

The example below shows the serialization with different parameters to `width` to adjust the indentation level.

    #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";
    }

Output:

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

    [1,2,4,8,16]

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

    [
      1,
      2,
      4,
      8,
      16
    ]

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

Example: (2) write JSON pointer to stream

The example below shows how to write a JSON pointer to a stream.

    #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;
    }

Output:

    /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.

Last update: July 28, 2022
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