std::vformat_to

Defined in header `<format>`
template< class OutputIt > OutputIt vformat_to( OutputIt out, std::string_view fmt, std::format_args args );	(1)	(since C++20)
template< class OutputIt > OutputIt vformat_to( OutputIt out, std::wstring_view fmt, std::wformat_args args );	(2)	(since C++20)
template< class OutputIt > OutputIt vformat_to( OutputIt out, const std::locale& loc, std::string_view fmt, std::format_args args );	(3)	(since C++20)
template< class OutputIt > OutputIt vformat_to( OutputIt out, const std::locale& loc, std::wstring_view fmt, std::wformat_args args );	(4)	(since C++20)

Format arguments held by args according to the format string fmt, and write the result to the output iterator out. If present, loc is used for locale-specific formatting.

Let CharT be decltype(fmt)::char_type (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<constCharT&>.

OutputIt must model (meet the semantic requirements of) the concept std::output_iterator<constCharT&>, and std::formatter<Ti,CharT> must meet the Formatter requirements for any Ti in the type of arguments. Otherwise, the behavior is undefined.

Parameters

out - iterator to the output buffer

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-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 the `std::formatter` specialization for the corresponding argument. 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 interpreted as chrono format specification.

For range types, the format specification is interpreted 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 thread id format specification and stacktrace entry format specification.
For std::basic_stacktrace, no format specifier is allowed.

(since C++23)

For std::filesystem::path, see path format specification.

(since C++26)

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

Throws std::format_error if fmt is not a valid format string for the provided arguments. Also propagates any exception thrown by formatter or iterator operations.

Example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.