std::print

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Input/output library

I/O manipulators
Print functions(C++23)
C-style I/O
Buffers
basic_streambuf
basic_filebuf
basic_stringbuf
basic_spanbuf (C++23)
strstreambuf (C++98/26*)
basic_syncbuf (C++20)
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ios_base
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File I/O
basic_ifstream
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String I/O
basic_istringstream
basic_ostringstream
basic_stringstream
Array I/O
basic_ispanstream (C++23)
basic_ospanstream (C++23)
basic_spanstream (C++23)
istrstream (C++98/26*)
ostrstream (C++98/26*)
strstream (C++98/26*)
Synchronized Output
basic_osyncstream (C++20)
Types
streamoff
streamsize
fpos
Error category interface
iostream_category (C++11)
io_errc (C++11)

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Print functions

Print functions
print (C++23)
println (C++23)
vprint_unicodevprint_unicode_buffered (C++23)(C++23)
vprint_nonunicodevprint_nonunicode_buffered (C++23)(C++23)

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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)

Formatargs according to the format stringfmt, and print the result to an output stream.

1) Equivalent tostd::print(stdout, fmt,std::forward<Args>(args)...).

2) If theordinary literal encoding is UTF-8, equivalent to(std::enable_nonlocking_formatter_optimization<std::remove_cvref_t<Args>>&& ...)
?std::vprint_unicode(stream, fmt.str,std::make_format_args(args...))
: std::vprint_unicode_buffered(stream, fmt.str,std::make_format_args(args...));.

Otherwise, equivalent to(std::enable_nonlocking_formatter_optimization<std::remove_cvref_t<Args>>&& ...)
?std::vprint_nonunicode(stream, fmt.str,std::make_format_args(args...))
: std::vprint_nonunicode_buffered(stream, fmt.str,std::make_format_args(args...));.

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

[edit]Parameters

stream - output file stream to write to

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.
std::system_error, if writing to the stream fails.
Propagates any exception thrown by usedformatters, 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)	Exposingstd::basic_format_string

[edit]Example

Run this code

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

Hello C++23!

[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
P3107R5	C++23	only buffered printing operations can be performed	can perform unbuffered printing operations
P3235R3	C++23	the names of the functions added byP3107R5 were misleading	changed the function names

[edit]See also

println (C++23)	same asstd::print except that each print is terminated by additional new line (function template)[edit]
print(std::ostream) (C++23)	outputsformatted representation of the arguments (function template)[edit]
format (C++20)	stores formatted representation of the arguments in a new string (function template)[edit]
format_to (C++20)	writes out formatted representation of its arguments through an output iterator (function template)[edit]
printffprintfsprintfsnprintf (C++11)	prints formatted output tostdout, a file stream or a buffer (function)[edit]