# Section (3) fmod

Section 3 Linux manual pages

## Name

fmod, fmodf, fmodl — floating-point remainder function

## Synopsis

`#include <math.h>`
 ```double fmod(``` double x, double y`)`;

 ```float fmodf(``` float x, float y`)`;

 ```long double fmodl(``` long double x, long double y`)`;

Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
`fmodf`(), `fmodl`():
`_ISOC99_SOURCE` || `_POSIX_C_SOURCE` >= 200112L || /* Since glibc 2.19:
*/ `_DEFAULT_SOURCE` || /* Glibc versions <= 2.19:
*/ `_BSD_SOURCE` || `_SVID_SOURCE`
Note Link with `−lm`.

## DESCRIPTION

These functions compute the floating-point remainder of dividing `x` by `y`. The return value is `x``n` * `y`, where `n` is the quotient of `x` / `y`, rounded toward zero to an integer.

## RETURN VALUE

On success, these functions return the value `x``n`*`y`, for some integer `n`, such that the returned value has the same sign as `x` and a magnitude less than the magnitude of `y`.

If `x` or `y` is a NaN, a NaN is returned.

If `x` is an infinity, a domain error occurs, and a NaN is returned.

If `y` is zero, a domain error occurs, and a NaN is returned.

If `x` is +0 (−0), and `y` is not zero, +0 (−0) is returned.

## ERRORS

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: `x` is an infinity

`errno` is set to EDOM (but see BUGS). An invalid floating-point exception (`FE_INVALID`) is raised.

Domain error: `y` is zero

`errno` is set to EDOM. An invalid floating-point exception (`FE_INVALID`) is raised.

## ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

 Interface Attribute Value `fmod`(), `fmodf`(), `fmodl`() Thread safety MT-Safe

## CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD, C89.

## BUGS

Before version 2.10, the glibc implementation did not set `errno` to EDOM when a domain error occurred for an infinite `x`.

This page is part of release 4.16 of the Linux `man-pages` project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.