std::print
From cppreference.com
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, | (2) | (since C++23) |
Format args according to the format string fmt, and print the result to an output stream.
1) Equivalent to std::print(stdout, fmt, std::forward<Args>(args)...).
2) If the ordinary 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...));.
?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...));.
?std::vprint_nonunicode(stream, fmt.str, std::make_format_args(args...))
: std::vprint_nonunicode_buffered(stream, fmt.str, std::make_format_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.
Contents |
[edit]Parameters
| stream | - | output file stream to write to | ||||||||||||||||||||||||||||||||||||||||||||||
| fmt | - | an object that represents the format string. The format string consists of
Each replacement field has the following format:
1) replacement field without a format specification 2) replacement field with a format specification
| ||||||||||||||||||||||||||||||||||||||||||||||
| 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
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 by P3107R5 were misleading | changed the function names |
[edit]See also
(C++23) | same as std::print except that each print is terminated by additional new line (function template) |
(C++23) | outputs formatted representation of the arguments (function template) |
(C++20) | stores formatted representation of the arguments in a new string (function template) |
(C++20) | writes out formatted representation of its arguments through an output iterator (function template) |
(C++11) | prints formatted output to stdout, a file stream or a buffer (function) |
