michael@0: /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef prenv_h___
michael@0: #define prenv_h___
michael@0: 
michael@0: #include "prtypes.h"
michael@0: 
michael@0: /*******************************************************************************/
michael@0: /*******************************************************************************/
michael@0: /****************** THESE FUNCTIONS MAY NOT BE THREAD SAFE *********************/
michael@0: /*******************************************************************************/
michael@0: /*******************************************************************************/
michael@0: 
michael@0: PR_BEGIN_EXTERN_C
michael@0: 
michael@0: /*
michael@0: ** PR_GetEnv() -- Retrieve value of environment variable
michael@0: ** 
michael@0: ** Description:
michael@0: ** PR_GetEnv() is modeled on Unix getenv().
michael@0: ** 
michael@0: ** 
michael@0: ** Inputs: 
michael@0: **   var -- The name of the environment variable
michael@0: ** 
michael@0: ** Returns:
michael@0: **   The value of the environment variable 'var' or NULL if
michael@0: ** the variable is undefined.
michael@0: ** 
michael@0: ** Restrictions:
michael@0: **   You'd think that a POSIX getenv(), putenv() would be
michael@0: **   consistently implemented everywhere. Surprise! It is not. On
michael@0: **   some platforms, a putenv() where the argument is of
michael@0: **   the form "name"  causes the named environment variable to
michael@0: **   be un-set; that is: a subsequent getenv() returns NULL. On
michael@0: **   other platforms, the putenv() fails, on others, it is a
michael@0: **   no-op. Similarly, a putenv() where the argument is of the
michael@0: **   form "name=" causes the named environment variable to be
michael@0: **   un-set; a subsequent call to getenv() returns NULL. On
michael@0: **   other platforms, a subsequent call to getenv() returns a
michael@0: **   pointer to a null-string (a byte of zero).
michael@0: ** 
michael@0: **   PR_GetEnv(), PR_SetEnv() provide a consistent behavior 
michael@0: **   across all supported platforms. There are, however, some
michael@0: **   restrictions and some practices you must use to achieve
michael@0: **   consistent results everywhere.
michael@0: ** 
michael@0: **   When manipulating the environment there is no way to un-set
michael@0: **   an environment variable across all platforms. We suggest
michael@0: **   you interpret the return of a pointer to null-string to
michael@0: **   mean the same as a return of NULL from PR_GetEnv().
michael@0: ** 
michael@0: **   A call to PR_SetEnv() where the parameter is of the form
michael@0: **   "name" will return PR_FAILURE; the environment remains
michael@0: **   unchanged. A call to PR_SetEnv() where the parameter is
michael@0: **   of the form "name=" may un-set the envrionment variable on
michael@0: **   some platforms; on others it may set the value of the
michael@0: **   environment variable to the null-string.
michael@0: ** 
michael@0: **   For example, to test for NULL return or return of the
michael@0: **   null-string from PR_GetEnv(), use the following code
michael@0: **   fragment:
michael@0: ** 
michael@0: **      char *val = PR_GetEnv("foo");
michael@0: **      if ((NULL == val) || ('\0' == *val)) { 
michael@0: **          ... interpret this as un-set ... 
michael@0: **      }
michael@0: ** 
michael@0: **   The caller must ensure that the string passed
michael@0: **   to PR_SetEnv() is persistent. That is: The string should
michael@0: **   not be on the stack, where it can be overwritten
michael@0: **   on return from the function calling PR_SetEnv().
michael@0: **   Similarly, the string passed to PR_SetEnv() must not be
michael@0: **   overwritten by other actions of the process. ... Some
michael@0: **   platforms use the string by reference rather than copying
michael@0: **   it into the environment space. ... You have been warned!
michael@0: ** 
michael@0: **   Use of platform-native functions that manipulate the
michael@0: **   environment (getenv(), putenv(), 
michael@0: **   SetEnvironmentVariable(), etc.) must not be used with
michael@0: **   NSPR's similar functions. The platform-native functions
michael@0: **   may not be thread safe and/or may operate on different
michael@0: **   conceptual environment space than that operated upon by
michael@0: **   NSPR's functions or other environment manipulating
michael@0: **   functions on the same platform. (!)
michael@0: ** 
michael@0: */
michael@0: NSPR_API(char*) PR_GetEnv(const char *var);
michael@0: 
michael@0: /*
michael@0: ** PR_SetEnv() -- set, unset or change an environment variable
michael@0: ** 
michael@0: ** Description:
michael@0: ** PR_SetEnv() is modeled on the Unix putenv() function.
michael@0: ** 
michael@0: ** Inputs: 
michael@0: **   string -- pointer to a caller supplied
michael@0: **   constant, persistent string of the form name=value. Where
michael@0: **   name is the name of the environment variable to be set or
michael@0: **   changed; value is the value assigned to the variable.
michael@0: **
michael@0: ** Returns: 
michael@0: **   PRStatus.
michael@0: ** 
michael@0: ** Restrictions: 
michael@0: **   See the Restrictions documented in the description of
michael@0: **   PR_GetEnv() in this header file.
michael@0: ** 
michael@0: ** 
michael@0: */
michael@0: NSPR_API(PRStatus) PR_SetEnv(const char *string);
michael@0: 
michael@0: PR_END_EXTERN_C
michael@0: 
michael@0: #endif /* prenv_h___ */