# 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&>.

`OutputIt` must model (meet the semantic requirements of) the concept std::output_iterator <const CharT&>, 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-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. 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

| 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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