std::vformat(3)

🌸 NAME 🌸

std::vformat - std::vformat — yes bestie, she's self-titled and the manual is the C++ Standard Libary one (that's the exact spelling from the header, keeping it 💅). This is the std::vformat(3) page, and it's giving iconic formatting-girl energy. ✨

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✨ SYNOPSIS ✨

Defined in header <format>

std::string vformat( std::string_view fmt, std::format_args args ); (1) (since C++20)
std::wstring vformat( std::wstring_view fmt, std::wformat_args args ); (2) (since C++20)
std::string vformat( const std::locale& loc, std::string_view fmt, std::format_args args ); (3) (since C++20)
std::wstring vformat( 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 return the result as a string. If present, loc is used for locale-specific formatting. 🫶

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🎀 PARAMETERS 🎀

• 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. 🚨 periodt, no mixing 🚨

• format-spec — the format specification defined by the std::formatter specialization for the corresponding argument. Cannot start with }.

Here's the vibe check on how format-spec gets interpreted:

• 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.

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💖 RETURN VALUE 💖

A string object holding the formatted result. Slay. ✨

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😭 EXCEPTIONS 😭

Throws std::format_error if fmt is not a valid format string for the provided arguments, or std::bad_alloc on allocation failure. Also propagates any exception thrown by formatter or iterator operations. so keep that in mind, bestie 💀

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🧚 EXAMPLE 🧚

// Run this code

#include <format>
#include <iostream>

template<typename... Args>
inline void println(const std::format_string<Args...> fmt, Args&&... args)
{
    std::cout << std::vformat(fmt.get(), std::make_format_args(args...)) << '\n';
}

int main()
{
    println("{}{} {}{}", "Hello", ',', "C++", -1 + 2 * 3 * 4);
}

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🖨️ OUTPUT 🖨️

Hello, C++23

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👀 SEE ALSO 👀

Honestly, the original See also section is empty — no entries listed, no extra refs, just vibes. We're not inventing any, bestie. 🫶

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Cute little sign-off from the footer: source/version/date is http://cppreference.com, 2024.06.10, std::vformat(3). Byeee, go format something gorgeous 💖✨