putenv - change or add an environment variable
The putenv() function adds or changes the value of
environment variables. The argument
string is of the form
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 returns zero on success, or
nonzero if an error occurs. In the event of an error,
set to indicate the cause.
Insufficient space to allocate new environment.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
The putenv() function is not required to be reentrant, and the one in glibc 2.0 is not, but the glibc 2.1 version is.
Since version 2.1.2, the glibc implementation conforms to SUSv2: the
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 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 versions 2.0 to 2.1.1 differ: a
copy of the string is used. On the one hand this causes a memory leak,
and on the other hand it violates SUSv2.
The 4.4BSD version, like glibc 2.0, uses a copy.
SUSv2 removes the
const from the prototype, and so does
The GNU C library implementation provides a nonstandard extension. If
string does not include an equal sign:
then the named variable is removed from the caller's environment.
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