# std::vformat_to

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< cpp‎ | utility‎ | format

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<const CharT&>.

The behavior is undefined if `OutputIt` does not model (meet the semantic requirements of) the concept std::output_iterator<const CharT&>, or if std::formatter<Ti, CharT> does not meet the Formatter requirements for any `Ti` in the type of arguments.

### 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-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
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

| This section is incomplete Reason: no example

### Defect reports

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

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
P2216R3 | C++20 | type of `args` is parameterized on `OutputIt` | not parameterized

### See also

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