putenv(3C) SDK R4.11 putenv(3C)
NAME
putenv - change or add value to environment
SYNOPSIS
#include <stdlib.h>
int putenv (char *string);
DESCRIPTION
string points to a string of the form ``name=value.'' putenv makes
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 becomes part of the environment, so
altering the string will change the environment. string should not
be a local (stack allocated) variable, since returning from the
current function and calling a new one will change the environment.
If name is later redefined by another putenv, string is no longer
used. It may be altered or reused without affecting the environment.
Return Values
putenv returns non-zero if it was unable to obtain enough space via
malloc for an expanded environment, otherwise zero.
Considerations for Threads Programming
+---------+-----------------------------+
| | async- |
|function | reentrant cancel cancel |
| | point safe |
+---------+-----------------------------+
|putenv | Y N N |
+---------+-----------------------------+
The environment information is global to all threads in a process.
Changes to the environment occur immediately for all threads in a
process. putenv calls should be made when other threads will not be
impacted by the call or can handle a change in the environment.
Many of the shared library functions rely on the environment
information in their processing. For instance, mktime relies on the
timezone information in the environment in order to calculate its
return value. If thread 1 issues a putenv call to change the timezone
before thread 2 issues a mktime call, thread 2 will have results
based on the the timezone thread 1 specified.
REFERENCES
exec(2), reentrant(3), getenv(3C), malloc(3C), environ(5),
NOTICES
putenv manipulates the environment pointed to by environ, and can be
used in conjunction with getenv. However, envp (the third argument
to main) is not changed.
This routine uses malloc(3C) to enlarge the environment.
After putenv is called, environmental variables are not in
alphabetical order. A potential error is to call the function putenv
with a pointer to an automatic variable as the argument and to then
exit the calling function while string is still part of the
environment.
Licensed material--property of copyright holder(s)