PUTENV(3C) Standard C Library Functions PUTENV(3C)
NAME
putenv - change or add value to environment
SYNOPSIS
#include <stdlib.h>
int putenv(
char *string);
DESCRIPTION
The
putenv() function 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.
The
string argument points to a string of the form
name=value. The
space used by
string is no longer used once a new string-defining
name is passed to
putenv(). If there is no equals sign (
=) present as
a separator, then
string is treated as the
name of an environment
variable to remove from the environment, as though
unsetenv(3C) had
been called.
The
putenv() function uses
malloc(3C) to enlarge the environment.
After
putenv() is called, environment variables are not in
alphabetical order.
RETURN VALUES
Upon successful completion,
putenv() returns 0. Otherwise, it returns
a non-zero value and sets
errno to indicate the error.
ERRORS
The
putenv() function may fail if:
ENOMEM Insufficient memory was available.
USAGE
The
putenv() function can be safely called from multithreaded
programs. Caution must be exercised when using this function and
getenv(3C) in multithreaded programs. These functions examine and
modify the environment list, which is shared by all threads in a
program. The system prevents the list from being accessed
simultaneously by two different threads. It does not, however,
prevent two threads from successively accessing the environment list
using
putenv() or
getenv().
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | Safe |
+--------------------+-----------------+
SEE ALSO
exec(2),
getenv(3C),
malloc(3C),
attributes(7),
environ(7),
standards(7)WARNINGS
The
string argument should not be an automatic variable. It should
be declared static if it is declared within a function because it
cannot be automatically declared. A potential error is to call
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.
June 22, 2016 PUTENV(3C)
