function adds or changes the value of environment
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
The string pointed to by string becomes part of the environment,
so altering the string changes the environment.
function returns zero on success,
or nonzero if an error occurs.
Insufficient space to allocate new environment.
SVr4, POSIX.1-2001, 4.3BSD.
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.
has to allocate a new array environ,
and the previous array was also allocated by
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
In particular, this string becomes part of the environment;
changing it later will change the environment.
(Thus, it is an error is to call
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.