DOKK / manpages / debian 11 / manpages-dev / modff.3.en
MODF(3) Linux Programmer's Manual MODF(3)

modf, modff, modfl - extract signed integral and fractional values from floating-point number

#include <math.h>
double modf(double x, double *iptr);
float modff(float x, float *iptr);
long double modfl(long double x, long double *iptr);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

modff(), modfl():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

These functions break the argument x into an integral part and a fractional part, each of which has the same sign as x. The integral part is stored in the location pointed to by iptr.

These functions return the fractional part of x.

If x is a NaN, a NaN is returned, and *iptr is set to a NaN.

If x is positive infinity (negative infinity), +0 (-0) is returned, and *iptr is set to positive infinity (negative infinity).

No errors occur.

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

Interface Attribute Value
modf (), modff (), modfl () Thread safety MT-Safe

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

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

frexp(3), ldexp(3)

This page is part of release 5.10 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/.

2017-09-15