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)):
modf(), modl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE; or cc -std=c99
The modf() function breaks 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.
The modf() function returns 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.
C99, POSIX.1-2001. The variant returning double also conforms to SVr4,
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