_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
These functions round x to the nearest integer
not larger in absolute value.
These functions return the rounded integer value.
If x is integral, infinite, or NaN, x itself is returned.
No errors occur.
These functions first appeared in glibc in version 2.1.
The integral value returned by these functions may be too large
to store in an integer type
To avoid an overflow, which will produce undefined results,
an application should perform a range check on the returned value
before assigning it to an integer type.