C++ Handbook

Header Reference: <format>

Header Reference: <format>

The formatting API centered on std::format and formatter customizations.

How to use this reference page

Use reference pages to confirm names, categories, nearby facilities, and the constraints that matter before writing or reviewing code.

  • Scan the top of the page first to identify the primary types, functions, or algorithm families involved.
  • Use the nearby-page links when your question is really about a companion header, related algorithm family, or broader subsystem.
  • Validate tricky behavior with a small compileable example before relying on memory for details like invalidation, ordering, allocation, or lifetime rules.

What header pages are for

Header reference pages are meant to answer a practical question quickly: what this header provides, when to reach for it, and which usage rules are easiest to get wrong.

  • Start here when you already know roughly which header you need but want a fast operational summary.
  • Use the example section below as a minimal pattern, then adapt it to your real container, ownership, text, or concurrency workflow.
  • Jump to broader index pages when you need exhaustive coverage rather than a header-focused summary.

Header Reference: <format>

Main facilities

What it provides

When to use it

Nearby pages

Minimal example

#include <format>
#include <string>

int main() {
    std::string line = std::format("value = {}", 42);
    return static_cast<int>(line.size());
}

What to verify before relying on this header

  • Whether the code needs ownership, borrowing, locale awareness, or low-allocation conversion behavior.
  • How errors are reported: stream state, parse result, exception, error code, or boolean match result.
  • Whether encoding, formatting, or lifetime assumptions need to be made explicit in the surrounding API.