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Name

putenv - change or add value to environment

Synopsis

#include <stdlib.h>

int putenv(const char *string);

MT-Level

Safe

Description

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 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().

Return Values

putenv() returns non-zero if it was unable to obtain enough space using malloc() for an expanded environment, otherwise zero is returned.

See Also

exec(2) , getenv(3C) , malloc(3C) , environ(5)

Notes

This routine uses malloc(3C) to enlarge the environment.

After putenv() is called, environment variables are not in alphabetical order.

string should not be an automatic variable.

string should be declared static if it is declared within a function because it cannot be automatically declared.

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.

putenv() can be safely called from a multi-thread program. However, care must still be taken when using putenv() and getenv(3C) in a multi-thread program. These routines examine and modify the environment list. This list is shared by all threads in a program. The system prevents the list from being accessed simultaneously by two different threads. However, it does not prevent two threads from successively accessing the environment list using putenv() or getenv(3C) .

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