C++ Handbook

Header Reference: <numbers>

Header Reference: <numbers>

Standard mathematical constants such as pi, e, and related compile-time numeric constants from <numbers>.

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: <numbers>

Main facilities

What this header is for

Use <numbers> to avoid hard-coded approximations for common mathematical constants.

Common patterns

Notes

Minimal example

#include <numbers>

int main() {
    // Start with the primary facility from <numbers>.
    // Then verify lifetime, invalidation, ordering, or error-handling rules.
    return 0;
}

What to verify before relying on this header

  • What the primary facility is, and whether the surrounding code needs runtime behavior, compile-time support, or both.
  • Which constraints, preconditions, or complexity guarantees matter most for your use case.
  • Which neighboring headers you should review before locking in an API or implementation choice.