putenv — change or add an environment variable
#include <stdlib.h>
int
putenv( |
char * | string) ; |
The putenv
() function adds
or changes the value of environment variables. The argument
string
is of the form
name
=value
. If name
does not already exist
in the environment, then string
is added to the
environment. If name
does exist, then the
value of name
in
the environment is changed to value
. The string pointed to
by string
becomes
part of the environment, so altering the string changes the
environment.
The putenv
() function is not
required to be reentrant, and the one in libc4, libc5 and
glibc 2.0 is not, but the glibc 2.1 version is.
Description for libc4, libc5, glibc: If the argument
string
is of the form
name
, and does not
contain an `=' character, then the variable name
is removed from the
environment. If putenv
() has to
allocate a new array environ
, and the previous
array was also allocated by putenv
(), then it will be freed. In no case
will the old storage associated to the environment variable
itself be freed.
The libc4 and libc5 and glibc 2.1.2 versions conform to
SUSv2: the pointer string
given to putenv
() is used. In particular, this
string becomes part of the environment; changing it later
will change the environment. (Thus, it is an error is to call
putenv
() with an automatic
variable as the argument, then return from the calling
function while string
is still part of the environment.) However, glibc 2.0-2.1.1
differs: a copy of the string is used. On the one hand this
causes a memory leak, and on the other hand it violates
SUSv2. This has been fixed in glibc 2.1.2.
The 4.4BSD version, like glibc 2.0, uses a copy.
SUSv2 removes the `const' from the prototype, and so does glibc 2.1.3.
clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
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