putenv - phpMan

PUTENV(3)                  Linux Programmer’s Manual                 PUTENV(3)



NAME
       putenv - change or add an environment variable

SYNOPSIS
       #include <stdlib.h>

       int putenv(char *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 environ-
       ment.

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 environ-
       ment;  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), clearenv(3), unsetenv(3), environ(5)



GNU                               1993-04-08                         PUTENV(3)

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