std::print - cppreference.com (original) (raw)

Defined in header
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.

Equivalent to std::print(stdout, fmt, std::forward<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.

[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 }. 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 range types, the format specification is interpreted as range format specification. For std::pair and std::tuple, the format specification is interpreted as tuple format specification. For std::thread::id and std::stacktrace_entry, see thread id format specification and stacktrace entry format specification. For std::basic_stacktrace, no format specifier is allowed. (since C++23) For other formattable types, the format specification is determined by user-defined formatter specializations.
args...	-	arguments to be formatted

[edit] 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.

[edit] 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

[edit] Example

#include #include #include 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:

[edit] Defect reports

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