All Numeric Constants and Ratio Helpers

All Numeric Constants and Ratio Helpers

A compact scan page for standard mathematical constants from <numbers> and compile-time rational helpers from <ratio>.

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.

All Numeric Constants and Ratio Helpers

Mathematical constants from `<numbers>`

std::numbers::e
std::numbers::pi
std::numbers::inv_pi
std::numbers::ln2
std::numbers::ln10
std::numbers::sqrt2
std::numbers::sqrt3
related constant templates and additional constants supported by the active standard mode

Compile-time rational helpers from `<ratio>`

std::ratio<Num, Den>
arithmetic and comparison helpers over ratios
standard SI-style aliases used throughout chrono-style facilities

Where these matter in practice

strongly typed duration and unit systems
constexpr-heavy numeric code
removing magic constants and hard-coded scaling factors from APIs

Practical rules

prefer named constants over copied decimal literals when they accurately represent the domain value
use ratio helpers when compile-time unit relationships matter, not as a substitute for runtime arithmetic
keep unit semantics visible in types when precision or scale conversions matter

Example in practice

int main() {
    // Pick one facility from this reference page.
    // Write the smallest program that exercises its main precondition,
    // complexity rule, or lifetime constraint before scaling up.
    return 0;
}