modf - Man Page

extract signed integral and fractional values from floating-point number


Math library (libm, -lm)


#include <math.h>

double modf(double x, double *iptr);
float modff(float x, float *iptr);
long double modfl(long double x, long double *iptr);

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 <= 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.

Return Value

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).

modf(), modff(), modfl()Thread safetyMT-Safe


C11, POSIX.1-2008.


C99, POSIX.1-2001.

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

See Also

frexp(3), ldexp(3)

Referenced By

frexp(3), ldexp(3).

The man pages modff(3) and modfl(3) are aliases of modf(3).

2023-10-31 Linux man-pages 6.06