fmod (3)  Linux Manuals
fmod: floatingpoint remainder function
NAME
fmod, fmodf, fmodl  floatingpoint 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);
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 floatingpoint 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 floatingpoint exception (FE_INVALID) is raised.
 Domain error: y is zero
 errno is set to EDOM. An invalid floatingpoint 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  MTSafe 
CONFORMING TO
C99, POSIX.12001, POSIX.12008.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.COLOPHON
This page is part of release 5.10 of the Linux manpages 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/manpages/.