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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |ATTRIBUTES |STANDARDS |HISTORY |BUGS |EXAMPLES |SEE ALSO |COLOPHON | |
fmod(3) Library Functions Manualfmod(3)fmod, fmodf, fmodl - floating-point remainder function
Math library (libm,-lm)
#include <math.h>double fmod(doublex, doubley);float fmodf(floatx, floaty);long double fmodl(long doublex, long doubley); Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):fmodf(),fmodl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
These functions compute the floating-point remainder of dividingx byy. The return value isx -n *y, wheren is the quotient ofx /y, rounded toward zero to an integer. To obtain the modulus, more specifically, the Least Positive Residue, you will need to adjust the result fromfmod() like so: z = fmod(x, y); if (z < 0) z += fabs(y); An alternate way to express this is withfmod(fmod(x, y) + y, y), but the secondfmod() usually costs way more than the one branch.
On success, these functions return the valuex - n*y, for some integern, such that the returned value has the same sign asx and a magnitude less than the magnitude ofy. Ifx ory is a NaN, a NaN is returned. Ifx is an infinity, a domain error occurs, and a NaN is returned. Ify is zero, a domain error occurs, and a NaN is returned. Ifx is +0 (-0), andy is not zero, +0 (-0) is returned.
Seemath_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 infinityerrno is set toEDOM(but see BUGS). An invalid floating- point exception (FE_INVALID) is raised. Domain error:y is zeroerrno is set toEDOM. An invalid floating-point exception (FE_INVALID) is raised.
For an explanation of the terms used in this section, seeattributes(7). ┌──────────────────────────────────────┬───────────────┬─────────┐ │Interface│Attribute│Value│ ├──────────────────────────────────────┼───────────────┼─────────┤ │fmod(),fmodf(),fmodl() │ Thread safety │ MT-Safe │ └──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
C99, POSIX.1-2001. The variant returningdouble also conforms to SVr4, 4.3BSD, C89.
Before glibc 2.10, the glibc implementation did not seterrno toEDOMwhen a domain error occurred for an infinitex.
The callfmod(372, 360) returns 12. The callfmod(-372, 360) returns -12. The callfmod(-372, -360) also returns -12.
remainder(3)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17fmod(3)Pages that refer to this page:remainder(3), remquo(3)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |