Used in security-conscious applications. If it is unavailable the assignment
environ = NULL;
will probably do.
The DGUX and Tru64 manpages write: If environ has been modified by anything other than the putenv(), getenv(), or clearenv() functions, then clearenv() will return an error and the process environment will remain unchanged.
getenv(3), putenv(3), setenv(3), unsetenv(3), environ(5)