#include <stdlib.h>

int clearenv(void);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

clearenv(): _SVID_SOURCE || _BSD_SOURCE


The clearenv() function clears the environment of all name-value pairs and sets the value of the external variable environ to NULL.


The clearenv() function returns zero on success, and a nonzero value on failure.


Available since glibc 2.0.


Various UNIX variants (DG/UX, HP-UX, QNX, ...). POSIX.9 (bindings for FORTRAN77). POSIX.1-1996 did not accept clearenv() and putenv(3), but changed its mind and scheduled these functions for some later issue of this standard (cf. B.4.6.1). However, POSIX.1-2001 adds only putenv(3), and rejected clearenv().


Used in security-conscious applications. If it is unavailable the assignment

    environ = NULL;

will probably do.

The DG/UX and Tru64 man pages write: If environ has been modified by anything other than the putenv(3), getenv(3), or clearenv() functions, then clearenv() will return an error and the process environment will remain unchanged.

RELATED TO clearenv…


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