putenv - change or add an environment variable
int putenv(char *string);
Feature Test Macro Requirements for glibc (see feature_test_macros
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE
() 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
added to the environment. If name
does exist, then the value of
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.
() function returns zero on success, or nonzero if an error
occurs. In the event of an error, errno
is set to indicate the cause.
- Insufficient space to allocate new environment.
For an explanation of the terms used in this section, see attributes
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
() 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 pointer
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
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 glibc 2.1.3.
The GNU C library implementation provides a nonstandard extension. If
does not include an equal sign:
then the named variable is removed from the caller's environment.