roundup(3)

roundup3

Round up in steps

Usage

#include <sys/param.h>

roundup(x, step);

Library

Standard C library (libc)

Overview

This macro rounds x to the nearest multiple of step that is not less than x.

It is typically used for rounding up a pointer to align it or increasing a buffer to be allocated.

This API is not designed to be generic, and doesn't work in some cases that are not important for the typical use cases described above. See CAVEATS.

Return value

This macro returns the rounded value.

Caveats

The arguments may be evaluated more than once.

x should be nonnegative, and step should be positive.

If x + step would overflow or wrap around, the behavior is undefined.

Releases

3 releases since Debian 12 (Bookworm); the text changed 2 times.

  1. 12
  2. 13
  3. Arch

Standards

None.

From man-pages 6.19-1 in Arch Linux 2026-11-01. Parsed by carta from the page's man source.