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std::format_to(3) C++ Standard Libary std::format_to(3) NAME std::format_to - std::format_to Synopsis Defined in header <format> template< class OutputIt, class... Args > OutputIt format_to( OutputIt out, std::format_string<Args...> fmt, (1) (since C++20) Args&&... args ); template< class OutputIt, class... Args > OutputIt format_to( OutputIt out, std::wformat_string<Args...> (2) (since C++20) fmt, Args&&... args ); template< class OutputIt, class... Args > OutputIt format_to( OutputIt out, const std::locale& loc, (3) (since C++20) std::format_string<Args...> fmt, Args&&... args ); template< class OutputIt, class... Args > OutputIt format_to( OutputIt out, const std::locale& loc, (4) (since C++20) std::wformat_string<Args...> fmt, Args&&... args ); Format args according to the format string fmt, and write the result to the output iterator out. If present, loc is used for locale-specific format- ting. 1) equivalent to return std::vformat_to(out, fmt.str, std::make_format_args(args...)); 2) equivalent to return std::vformat_to(std::move(out), fmt.str, std::make_wformat_args(args...)); 3) equivalent to return std::vformat_to(out, loc, fmt.str, std::make_format_args(args...)); 4) equivalent to return std::vformat_to(std::move(out), loc, fmt.str, std::make_wformat_args(args...)); Let CharT be char for overloads (1,3), wchar_t for overloads (2,4). These overloads participate in overload resolution only if OutputIt satisfies the concept std::output_iterator<const CharT&>. The behavior is undefined if OutputIt does not model (meet the se- mantic requirements of) the concept std::output_iterator<const CharT&>, or if std::for- matter<Ti, CharT> does not meet the BasicFormatter requirements for any Ti in Args (as required by std::make_format_args and std::make_wformat_args). Parameters out - iterator to the output buffer 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 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. arg-id - The arg-ids in a format string must all be present or all be omitted. Mixing manual and automatic in- dexing is an error. fmt - the format specification defined by the std::formatter format-spec - specialization for the corresponding argu- ment. 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 inter- preted as chrono format specification. * For range types, the format specification is inter- preted 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 (since C++23) thread id format specification and stacktrace entry format specification. * For std::basic_stacktrace, no format specifier is allowed. * For std::filesystem::path, see path format (since C++26) specification. * For other formattable types, the format specification is determined by user-defined formatter specializations. args... - arguments to be formatted loc - std::locale used for locale-specific formatting Return value Iterator past the end of the output range. Exceptions Propagates any exception thrown by formatter or iterator operations. Notes As of P2216R3, it is an error if the format string is not a constant expression. std::vformat_to or std::runtime_format (since C++26) can be used in this case. Example // Run this code #include <format> #include <iostream> #include <iterator> #include <string> auto main() -> int { std::string buffer; std::format_to( std::back_inserter(buffer), //< OutputIt "Hello, C++{}!\n", //< fmt "20"); //< arg std::cout << buffer; buffer.clear(); std::format_to( std::back_inserter(buffer), //< OutputIt "Hello, {0}::{1}!{2}", //< fmt "std", //< arg {0} "format_to()", //< arg {1} "\n", //< arg {2} "extra param(s)..."); //< unused std::cout << buffer; std::wstring wbuffer; std::format_to( std::back_inserter(wbuffer),//< OutputIt L"Hello, {2}::{1}!{0}", //< fmt L"\n", //< arg {0} L"format_to()", //< arg {1} L"std", //< arg {2} L"...is not..." //< unused L"...an error!"); //< unused std::wcout << wbuffer; } Output: Hello, C++20! Hello, std::format_to()! Hello, std::format_to()! Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior P2216R3 C++20 throws std::format_error for invalid format string results in invalid format string compile-time er- ror objects that are neither P2418R2 C++20 const-usable nor copyable allow formatting these objects (such as generator-like objects) are not formattable P2508R1 C++20 there's no user-visible name for the name ba- sic_format_string is this facility exposed See also format stores formatted representation of the arguments in a new string (C++20) (function template) format_to_n writes out formatted representation of its arguments through an output (C++20) iterator, not exceeding specified size (function template) http://cppreference.com 2024.06.10 std::format_to(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Notes | Example | Output: | See also
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