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std:: println

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< cpp ‎ | io
C++
Input/output library
Print functions
Print functions
(C++23)
println
(C++23)
(C++23) (C++23)
(C++23) (C++23)
Defined in header <print>
template < class ... Args >
void println ( std:: format_string < Args... > fmt, Args && ... args ) ;
(1) (since C++23)
template < class ... Args >

void println ( std:: FILE * stream,

std:: format_string < Args... > fmt, Args && ... args ) ;
(2) (since C++23)
void println ( ) ;
(3) (since C++26)
void println ( std:: FILE * stream ) ;
(4) (since C++26)

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 :: println ( stdout , fmt, std:: forward < Args > ( args ) ... ) .
2) Equivalent to performing the following operations:

std:: print ( stream, "{} \n " , std:: format ( fmt, std:: forward < Args > ( args ) ... ) ) ;

(until C++26)

std:: print ( stream, std:: runtime_format ( std:: string ( fmt. get ( ) ) + ' \n ' ) ,
std:: forward < Args > ( args ) ... )

(since C++26)
3) Equivalent to std :: println ( stdout ) .
4) Equivalent to std:: print ( stream, " \n " ) .

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

Contents

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-id s 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. Cannot start with } .

(since C++23)
(since C++26)
  • For other formattable types, the format specification is determined by user-defined formatter specializations.
args... - arguments to be formatted

Exceptions

Notes

Although overloads ( 3,4 ) are added in C++26, all known implementations make them available in C++23 mode.

Feature-test macro Value Std Feature
__cpp_lib_print 202207L (C++23) Formatted output
202403L (C++26) Unbuffered formatted output [1]
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string
  1. ↑ Although P3107R5 is accepted as a DR, std::runtime_format is only available since C++26. As a result, the resolution cannot be applied in C++23.

Example

Run this code 
#include <print>
int main()
{
    // Each call to std::println ends with new-line
    std::println("Please"); // overload (1)
    std::println("enter"); // (1)
    std::print("pass");
    std::print("word");
    std::println(); // (3); valid since C++26; 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)