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PUTENV
!!!PUTENV
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
NOTES
CONFORMING TO
SEE ALSO
----
!!NAME


putenv - change or add an environment variable
!!SYNOPSIS


__#include
__''string''__);
__
!!DESCRIPTION


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.
!!RETURN VALUE


The __putenv()__ function returns zero on success, or -1
if an error occurs.
!!ERRORS


__ENOMEM__


Insufficient space to allocate new environment.
!!NOTES


The __putenv()__ function is not required to be
reentrant, and the one in libc4, libc5 and glibc2.0 is not,
but the glibc2.1 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 glibc2.1.2.


The BSD4.4 version, like glibc 2.0, uses a
copy.


SUSv2 removes the `const' from the prototype, and so does
glibc 2.1.3.
!!CONFORMING TO


SVID 3, POSIX, BSD 4.3
!!SEE ALSO


getenv(3), setenv(3), unsetenv(3),
environ(7)
----

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Last edited on Tuesday, June 4, 2002 12:24:30 am by "perry"

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