# fmod man page

fmod, fmodf, fmodl — floating-point remainder function

## Synopsis

#include <math.h> double fmod(doublex, doubley); float fmodf(floatx, floaty); long double fmodl(long doublex, long doubley);

`Link with `

*-lm*.

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

## 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*.

## See Also

## Colophon

This page is part of release 4.15 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/.

## Referenced By

The man pages fmodf(3) and fmodl(3) are aliases of fmod(3).