Section: Linux Programmer's Manual (3)
putenv - change or add an environment variable
int putenv(char *string);
Feature Test Macro Requirements for glibc (see
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE
function adds or changes the value of environment
The argument string
is of the form name
does not already exist in the environment, then
is added to the environment.
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.
In the event of an error,
is set to indicate the cause.
Insufficient space to allocate new environment.
For an explanation of the terms used in this section, see
||Thread safety||MT-Unsafe const:env|
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 string given to
In particular, this string becomes part of the environment;
changing it later will change the environment.
(Thus, it is an error 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 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.
does not include an equal sign:
then the named variable is removed from the caller's environment.
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