std::println

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

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

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.

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 std::filesystem::path, see path format specification.

(since C++26)

For other formattable types, the format specification is determined by user-defined formatter specializations.

args... - arguments to be formatted

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

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
`__cpp_lib_print`	`202403L`	(C++26) (DR23)	Unbuffered formatted output
`__cpp_lib_format`	`202207L`	(C++23)	Exposing `std::basic_format_string`

Example

#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

print (C++23)	prints to `stdout` or a file stream using formatted representation of the arguments (function template)
println(std::ostream) (C++23)	outputs formatted representation of the arguments with appended `'\n'` (function template)
format (C++20)	stores formatted representation of the arguments in a new string (function template)
printffprintfsprintfsnprintf (C++11)	prints formatted output to `stdout`, a file stream or a buffer (function)

std::println

Parameters

Exceptions

Notes

Example

See also