The modf() and modff() functions break the argument x into integral and fractional parts, each of which has the same sign as the argument. The modf() function stores the integral part as a double in the object pointed to by iptr. The modff() function stores the integral part as a float in the object pointed to by iptr.

Upon successful completion, modf() and modff() return the signed fractional part of x.

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

If the correct value would cause underflow to 0.0, modf() returns 0 and errno may be set to ERANGE.

The modf() function may fail if:

ERANGE

The result underflows.

An application wishing to check for error situations should set errno to 0 before calling modf(). If errno is non-zero on return, or the return value is NaN, an error has occurred.

See attributes(5) for descriptions of the following attributes:

frexp(3C), isnan(3M), ldexp(3C), attributes(5)