std::vformat_to(3)

Okay so bestie, welcome to the std::vformat_to(3) page from the C++ Standard Libary manual 💅✨ we’re gonna get through this together, no cap.

🌸 NAME 🌸

std::vformat_to — literally std::vformat_to, that’s the name, iconic.

✨ SYNOPSIS ✨

Defined in header <format>:

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

OutputIt vformat_to( OutputIt out, const std::locale& loc,
(3) (since C++20)

std::string_view fmt, std::format_args args
);
template< class OutputIt >

OutputIt vformat_to( OutputIt out, const std::locale& loc,
(4) (since C++20)

std::wstring_view fmt, std::wformat_args args
);

Okay so what it actually does: it formats the arguments held by args according to the format string fmt, and writes the result to the output iterator out. If loc is present, it’s used for locale-specific formatting. Periodt 💖

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. Like, actually undefined, bestie — not a vibe 💀

🎀 PARAMETERS 🎀

• out — iterator to the output buffer. Simple as that.
• 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. (since C++23)
  • 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.
  • 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. That’s it, that’s the return value 💅

😭 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. So like, catch it or whatever 🫶

💀 EXAMPLE 💀

This section is incomplete. Reason: no example.

Not me getting no example 😭 the audacity.

🧚 DEFECT REPORTS 🧚

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

• DR: P2216R3 — Applied to: C++20; Behavior as published: type of args is parameterized on OutputIt; Correct behavior: not parameterized.

👀 SEE ALSO 👀

No see-also entries were listed here, literally nothing but the category note.

📚 Category

• Todo no example

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