Docs4dev
Docs
cpp / latest / io / println.html

std::println

Defined in header <print> 
template< class... Args >
void println( std::FILE* stream,
              std::format_string<Args...> fmt, Args&&... args );
 (1) (since C++23) 
template< class... Args >
void println( std::format_string<Args...> fmt, Args&&... args );
 (2) (since C++23)

Format args according to the format string fmt with appended '\n' (which means that each output ends with a new-line), and print the result to a stream.

1) Equivalent to: std::print(stream, "{}\n", std::format(fmt, args...));
2) same as (1) when stream is equal to the standard C output stream stdout, i.e. std::println(stdout, fmt, args...);

The behavior is undefined if std::formatter<Ti, char> does not meet the BasicFormatter requirements for any Ti in Args (as required by std::make_format_args).

Parameters

stream - output file stream to write to
fmt - an object that represents the format string. The format string consists of
  • ordinary characters (except { and }), which are copied unchanged to the output,
  • escape sequences {{ and }}, which are replaced with { and } respectively in the output, and
  • replacement fields.

Each replacement field has the following format:

{ arg-id (optional) } (1)
{ arg-id (optional) : format-spec } (2)
1) replacement field without a format specification 2) replacement field with a format specification
arg-id - specifies the index of the argument in args whose value is to be used for formatting; if it is omitted, the arguments are used in order.

The arg-ids in a format string must all be present or all be omitted. Mixing manual and automatic indexing is an error.
format-spec - the format specification defined by the std::formatter specialization for the corresponding argument.
(since C++23)
  • For other formattable types, the format specification is determined by user-defined formatter specializations.
args... - arguments to be formatted

Return value

(none)

Exceptions

Notes

Feature-test macro Value Std Feature
__cpp_lib_print 202207L (C++23) Formatted output
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string

Example

#include <print>
 
int main()
{
    // Each call to std::println ends with new-line
    std::println("Please");
    std::println("enter");
 
    std::print("pass");
    std::print("word");
 
    std::println(""); // same effect as std::print("\n");
}

Output:

Please
enter
password

See also

(C++23)
prints to stdout or a file stream using formatted representation of the arguments
(function template)
(C++23)
outputs formatted representation of the arguments with appended '\n'
(function template)
(C++20)
stores formatted representation of the arguments in a new string
(function template)
(C++11)
prints formatted output to stdout, a file stream or a buffer
(function)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/io/println