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std::print

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

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

1) if the ordinary literal encoding is UTF-8, equivalent to:

std::vprint_unicode(stream, fmt.get(),
    std::make_format_args(std::forward<Args>(args)...));

Otherwise, equivalent to:

std::vprint_nonunicode(stream, fmt.get(), 
    std::make_format_args(std::forward<Args>(args)...));

2) same as (1) with the standard C output stream stdout bound to stream, i.e.

std::print(stdout, fmt, std::forward<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).

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.

For basic types and standard string types, the format specification is interpreted as standard format specification.
For chrono types, the format specification is interpreted as chrono format specification.
For std::thread::id, the format specification is interpreted as thread id format specification.
For other formattable types, the format specification is determined by user-defined formatter specializations.

args... - arguments to be formatted

Return value

(none).

Exceptions

std::bad_alloc on allocation failure.
std::system_error, if writing to the stream fails.
Propagates any exception thrown by used formatters, e.g. std::format_error.

Notes

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

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!