std::println(std::ostream)

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Defined in header`<ostream>`
template<class...Args> void println(std::ostream& os,std::format_string<Args...> fmt, Args&&...args);	(1)	(since C++23)
void println(std::ostream& os);	(2)	(since C++26)

Formatsargs according to the format stringfmt with appended'\n' (which means that each output ends with a new-line), and inserts the result intoos stream.

1) Equivalent to:std::print(os,"{}\n",std::format(os.getloc(), fmt, args...));

2) Equivalent to:std::print(os,"\n");

The behavior is undefined ifstd::formatter<Ti,char> does not meet theBasicFormatter requirements for anyTi inArgs (as required bystd::make_format_args).

[edit]Parameters

os - output stream to insert data into

fmt

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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. Thearg-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 thestd::formatter specialization for the corresponding argument. Cannot start with}.

For basic types and standard string types, the format specification is interpreted asstandard format specification.
For chrono types, the format specification is interpreted aschrono format specification.

For range types, the format specification is interpreted asrange format specification.
Forstd::pair andstd::tuple, the format specification is interpreted astuple format specification.
Forstd::thread::id andstd::stacktrace_entry, seethread id format specification andstacktrace entry format specification.
Forstd::basic_stacktrace, no format specifier is allowed.

(since C++23)

Forstd::filesystem::path, seepath format specification.

(since C++26)

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

args... - arguments to be formatted

[edit]Exceptions

std::bad_alloc on allocation failure.
Propagate any exception thrown by anyformatter, e.g.std::format_error, without regard to the value ofos.exceptions() and without turning onios_base::badbit in the error state ofos.
May throwios_base::failure caused byos.setstate(ios_base::badbit) which is called if an insertion intoos fails.

[edit]Notes

Although overload(2) is added in C++26, all known implementations make it available in C++23 mode.

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

[edit]Example

This section is incomplete
Reason: no example

[edit]Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 4088	C++23	(1) ignored the locale imbued inos in formatting arguments	such locale is used

[edit]See also

print(std::ostream) (C++23)	outputsformatted representation of the arguments (function template)[edit]
println (C++23)	same asstd::print except that each print is terminated by additional new line (function template)[edit]
format (C++20)	stores formatted representation of the arguments in a new string (function template)[edit]