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std:: print

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

void print ( std:: FILE * stream,

std:: format_string < Args... > fmt, Args && ... args ) ;
(2) (since C++23)

Format args according to the format string fmt , and print the result to an output stream.

1) Equivalent to std :: print ( stdout , fmt, std:: forward < Args > ( args ) ... ) .
2) If the ordinary literal encoding is UTF-8, equivalent to ( std :: enable_nonlocking_formatter_optimization < std:: remove_cvref_t < Args >> && ... )
? std:: vprint_unicode ( stream, fmt. str , std:: make_format_args ( args... ) )
: std :: vprint_unicode_buffered ( stream, fmt. str , std:: make_format_args ( args... ) ) ; .
Otherwise, equivalent to ( std :: enable_nonlocking_formatter_optimization < std:: remove_cvref_t < Args >> && ... )
? std:: vprint_nonunicode ( stream, fmt. str , std:: make_format_args ( args... ) )
: std :: vprint_nonunicode_buffered ( stream, fmt. str , std:: make_format_args ( args... ) ) ; .

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

Feature-test macro Value Std Feature
__cpp_lib_print 202207L (C++23) Formatted output
202403L (C++26)
(DR23) 		Unbuffered formatted output
202406L (C++26)
(DR23) 		Enabling unbuffered formatted output for more formattable types
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string

Example

Run this code 
#include <cstdio>
#include <filesystem>
#include <print>
int main()
{
    std::print("{2} {1}{0}!\n", 23, "C++", "Hello");  // overload (1)
    const auto tmp{std::filesystem::temp_directory_path() / "test.txt"};
    if (std::FILE* stream{std::fopen(tmp.c_str(), "w")})
    {
        std::print(stream, "File: {}", tmp.string()); // overload (2)
        std::fclose(stream);
    }
}

Output: 

Hello C++23!

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P3107R5 C++23 only buffered printing operations can be performed can perform unbuffered printing operations
P3235R3 C++23 the names of the functions added
by P3107R5 were misleading 		changed the function names

See also

(C++23)
same as std::print except that each print is terminated by additional new line
(function template)
(C++23)
outputs formatted representation of the arguments
(function template)
(C++20)
stores formatted representation of the arguments in a new string
(function template)
(C++20)
writes out formatted representation of its arguments through an output iterator
(function template)
(C++11)
prints formatted output to stdout , a file stream or a buffer
(function)