These functions shall break the argument x into integral and fractional
parts, each of which has the same sign as the argument. It stores the integral
part as a double (for the modf() function), a float (for
the modff() function), or a long double (for the modfl()
function), in the object pointed to by iptr.
Upon successful completion, these functions shall return the signed fractional
part of x.
If x is NaN, a NaN shall be returned, and *iptr shall be set to a
If x is ±Inf, ±0 shall be returned, and *iptr shall
be set to ±Inf.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html