Namespaces
Variants
Views
Actions

std::print

From cppreference.com
< cpp‎ | io
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_locking(stream, fmt.str, make_format_args(args...))
    : std::vprint_unicode(stream, fmt.str, make_format_args(args...));
.
Otherwise, equivalent to (std::enable_nonlocking_formatter_optimization<std::remove_cvref_t<Args>> && ...)
    ? std::vprint_nonunicode_locking(stream, fmt.str, make_format_args(args...))
    : std::vprint_nonunicode(stream, fmt.str, make_format_args(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).

Contents

[edit] 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

[edit] Exceptions

[edit] Notes

Feature-test macro Value Std Feature
__cpp_lib_print 202207L (C++23) Formatted output
202403L (C++26)
(DR23)
Formatted output with stream locking
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string

[edit] Example

#include <cstdio>
#include <filesystem>
#include <print>
 
int main()
{
    std::print("{0} {2}{1}!\n", "Hello", 23, "C++"); // overload (2)
 
    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 (1)
        std::fclose(stream);
    }
}

Output:

Hello C++23!

[edit] See also

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