FreeBSD Manual Pages
std::format_to_n(3) C++ Standard Libary std::format_to_n(3) NAME std::format_to_n - std::format_to_n Synopsis Defined in header <format> template< class OutputIt, class... Args > std::format_to_n_result<OutputIt> (1) (since C++20) format_to_n( OutputIt out, std::iter_difference_t<OutputIt> n, /*format_string<Args...>*/ fmt, Args&&... args ); template< class OutputIt, class... Args > std::format_to_n_result<OutputIt> (2) (since C++20) format_to_n( OutputIt out, std::iter_difference_t<OutputIt> n, /*wformat_string<Args...>*/ fmt, Args&&... args ); template< class OutputIt, class... Args > std::format_to_n_result<OutputIt> format_to_n( OutputIt out, std::iter_difference_t<OutputIt> n, (3) (since C++20) const std::locale& loc, /*format_string<Args...>*/ fmt, Args&&... args ); template< class OutputIt, class... Args > std::format_to_n_result<OutputIt> format_to_n( OutputIt out, std::iter_difference_t<OutputIt> n, (4) (since C++20) const std::locale& loc, /*wformat_string<Args...>*/ fmt, Args&&... args ); template< class OutputIt > struct format_to_n_result { OutputIt out; (5) (since C++20) std::iter_difference_t<OutputIt> size; }; Format args according to the format string fmt, and write the result to the output iterator out. At most n characters are written. If present, loc is used for locale-specific formatting. 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::formatter<std::remove_cvref_t<Ti>, CharT> does not meet the Ba- sicFormatter requirements for any Ti in Args. 5) std::format_to_n_result has no base classes, or members other than out, size and implicitly declared special member functions. Parameters out - iterator to the output buffer n - maximum number of characters to be written to the buffer parameter of unspecified type, whose initialization is valid only if the argument is convertible to std::string_view (for (1,3)) or std::wstring_view (for (2,4)), and the result of conver- sion is a constant expression and a valid format string for Args. 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) fmt - 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 arg-id - are used in order. The arg-ids in a format string must all be present or all be omitted. Mixing manual and automatic index- ing is an error. format-spec - the format specification defined by the std::formatter specialization for the corresponding argu- ment. * 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 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 A format_to_n_result such that the out member is an iterator past the end of the output range, and the size member is the total (not truncated) out- put size. Exceptions Propagates any exception thrown by formatter or iterator operations. Example // Run this code #include <format> #include <iostream> #include <string_view> int main() { char buffer[64]; const auto result = std::format_to_n(buffer, std::size(buffer) - 1, "Hubble's H{2} {3} {0}{4}{1} km/sec/Mpc.", 71, // {0}, occupies 2 bytes 8, // {1}, occupies 1 byte "\u2080", // {2}, occupies 3 bytes "\u2245", // {3}, occupies 3 bytes "\u00B1" // {4}, occupies 2 bytes ); *result.out = '\0'; const std::string_view str{buffer, result.out}; // uses C++20 ctor std::cout << "Buffer: \"" << str << "\"\n" << "Buffer size = " << std::size(buffer) << '\n' << "Untruncated output size = " << result.size << '\n'; } Output: Buffer: "Hubble's H 718 km/sec/Mpc." Buffer size = 64 Untruncated output size = 35 Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Cor- rect behavior throws std::format_error for invalid invalid format string P2216R3 C++20 format string results in compile-time error objects that are neither const-usable nor P2418R2 C++20 copyable allow formatting these (such as generator-like objects) are not objects formattable See also format stores formatted representation of the arguments in a new string (C++20) (function template) format_to writes out formatted representation of its arguments through an (C++20) output iterator (function template) formatted_size determines the number of characters necessary to store the formatted (C++20) representation of its arguments (function template) http://cppreference.com 2022.07.31 std::format_to_n(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Example | Output: | See also
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::format_to_n&sektion=3&manpath=FreeBSD+Ports+15.0>