man putenv () - change or add a value to an environment

NAME

putenv - change or add a value to an environment

SYNOPSIS

#include <stdlib.h>

int putenv(char *string);

DESCRIPTION

The putenv() function shall use the string argument to set environment variable values. The string argument should point to a string of the form " name= value ". The putenv() function shall make the value of the environment variable name equal to value by altering an existing variable or creating a new one. In either case, the string pointed to by string shall become part of the environment, so altering the string shall change the environment. The space used by string is no longer used once a new string which defines name is passed to putenv().

The putenv() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

RETURN VALUE

Upon successful completion, putenv() shall return 0; otherwise, it shall return a non-zero value and set errno to indicate the error.

ERRORS

The putenv() function may fail if:

ENOMEM
Insufficient memory was available.

The following sections are informative.

EXAMPLES

Changing the Value of an Environment Variable

The following example changes the value of the HOME environment variable to the value /usr/home. 

#include <stdlib.h>
...
static char *var = "HOME=/usr/home";
int ret;


ret = putenv(var);



APPLICATION USAGE

The putenv() function manipulates the environment pointed to
by environ, and can be used in conjunction with getenv().


See exec() , for restrictions on changing the environment in
multi-threaded applications.


This routine may use malloc() to enlarge the environment.


A potential 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.


The setenv() function is preferred over this function.

RATIONALE

The standard developers noted that putenv() is the only function
available to add to the environment without permitting
memory leaks.

FUTURE DIRECTIONS

None.

SEE ALSO

exec() , getenv() , malloc() , setenv() ,
the Base Definitions volume of
IEEE Std 1003.1-2001, <stdlib.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .