std::print

 

C++

Compiler support

Freestanding and hosted

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Named requirements

Feature test macros (C++20)

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Ranges library (C++20)

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Technical specifications

Symbols index

External libraries

 

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 (deprecated in C++98)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

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basic_ifstream

basic_ofstream

basic_fstream

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basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

Print functions

Print functions

print (C++23)

println (C++23)

vprint_unicode (C++23)

vprint_nonunicode (C++23)

 

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

Run this code

#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!

See also

println (C++23)	same as std::print except that each print is terminated by additional new line (function template)
print(std::ostream) (C++23)	outputs formatted representation of the arguments (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)