These functions shall return the integral value (represented as a double)
nearest x in the direction of the current rounding mode. The current
rounding mode is implementation-defined.
If the current rounding mode rounds toward negative infinity, then rint()
shall be equivalent to floor() . If the current rounding mode rounds
toward positive infinity, then rint() shall be equivalent to
These functions differ from the nearbyint(), nearbyintf(), and
nearbyintl() functions only in that they may raise the inexact
floating-point exception if the result differs in value from the argument.
An application wishing to check for error situations should set errno to
zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
functions. On return, if errno is non-zero or
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
non-zero, an error has occurred.
Upon successful completion, these functions shall return the integer
(represented as a double precision number) nearest x in the direction
of the current rounding mode.
If x is NaN, a NaN shall be returned.
If x is ±0 or ±Inf, x shall be returned.
If the correct value would cause overflow, a range error shall occur and
rint(), rintf(), and rintl() shall return the value of
the macro ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (with the
same sign as x), respectively.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then
errno shall be set to [ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow
floating-point exception shall be raised.
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