function clears the environment of all name-value
pairs and sets the value of the external variable
function returns zero on success, and a nonzero
value on failure.
Not in libc4, libc5.
In glibc since glibc 2.0.
Various Unix variants (DG/UX, HP-UX, QNX, ...).
POSIX.9 (bindings for FORTRAN77).
POSIX.1-1996 did not accept
but changed its mind and scheduled these functions for some
later issue of this standard (cf. B.4.6.1).
Used in security-conscious applications.
If it is unavailable
environ = NULL;
will probably do.
The DG/UX and Tru64 man pages write: If
has been modified by anything other than the
will return an error and the process environment will remain unchanged.