nsprpub/pr/include/prenv.h

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  37
  38 #ifndef prenv_h___
  39 #define prenv_h___
  40
  41 #include "prtypes.h"
  42
  43 /*******************************************************************************/
  44 /*******************************************************************************/
  45 /****************** THESE FUNCTIONS MAY NOT BE THREAD SAFE *********************/
  46 /*******************************************************************************/
  47 /*******************************************************************************/
  48
  49 PR_BEGIN_EXTERN_C
  50
  51 /*
  52 ** PR_GetEnv() -- Retrieve value of environment variable
  53 **
  54 ** Description:
  55 ** PR_GetEnv() is modeled on Unix getenv().
  56 **
  57 **
  58 ** Inputs:
  59 **   var -- The name of the environment variable
  60 **
  61 ** Returns:
  62 **   The value of the environment variable 'var' or NULL if
  63 ** the variable is undefined.
  64 **
  65 ** Restrictions:
  66 **   You'd think that a POSIX getenv(), putenv() would be
  67 **   consistently implemented everywhere. Surprise! It is not. On
  68 **   some platforms, a putenv() where the argument is of
  69 **   the form "name"  causes the named environment variable to
  70 **   be un-set; that is: a subsequent getenv() returns NULL. On
  71 **   other platforms, the putenv() fails, on others, it is a
  72 **   no-op. Similarly, a putenv() where the argument is of the
  73 **   form "name=" causes the named environment variable to be
  74 **   un-set; a subsequent call to getenv() returns NULL. On
  75 **   other platforms, a subsequent call to getenv() returns a
  76 **   pointer to a null-string (a byte of zero).
  77 **
  78 **   PR_GetEnv(), PR_SetEnv() provide a consistent behavior
  79 **   across all supported platforms. There are, however, some
  80 **   restrictions and some practices you must use to achieve
  81 **   consistent results everywhere.
  82 **
  83 **   When manipulating the environment there is no way to un-set
  84 **   an environment variable across all platforms. We suggest
  85 **   you interpret the return of a pointer to null-string to
  86 **   mean the same as a return of NULL from PR_GetEnv().
  87 **
  88 **   A call to PR_SetEnv() where the parameter is of the form
  89 **   "name" will return PR_FAILURE; the environment remains
  90 **   unchanged. A call to PR_SetEnv() where the parameter is
  91 **   of the form "name=" may un-set the envrionment variable on
  92 **   some platforms; on others it may set the value of the
  93 **   environment variable to the null-string.
  94 **
  95 **   For example, to test for NULL return or return of the
  96 **   null-string from PR_GetEnv(), use the following code
  97 **   fragment:
  98 **
  99 **      char *val = PR_GetEnv("foo");
 100 **      if ((NULL == val) || ('\0' == *val)) {
 101 **          ... interpret this as un-set ...
 102 **      }
 103 **
 104 **   The caller must ensure that the string passed
 105 **   to PR_SetEnv() is persistent. That is: The string should
 106 **   not be on the stack, where it can be overwritten
 107 **   on return from the function calling PR_SetEnv().
 108 **   Similarly, the string passed to PR_SetEnv() must not be
 109 **   overwritten by other actions of the process. ... Some
 110 **   platforms use the string by reference rather than copying
 111 **   it into the environment space. ... You have been warned!
 112 **
 113 **   Use of platform-native functions that manipulate the
 114 **   environment (getenv(), putenv(),
 115 **   SetEnvironmentVariable(), etc.) must not be used with
 116 **   NSPR's similar functions. The platform-native functions
 117 **   may not be thread safe and/or may operate on different
 118 **   conceptual environment space than that operated upon by
 119 **   NSPR's functions or other environment manipulating
 120 **   functions on the same platform. (!)
 121 **
 122 */
 123 NSPR_API(char*) PR_GetEnv(const char *var);
 124
 125 /*
 126 ** PR_SetEnv() -- set, unset or change an environment variable
 127 **
 128 ** Description:
 129 ** PR_SetEnv() is modeled on the Unix putenv() function.
 130 **
 131 ** Inputs:
 132 **   string -- pointer to a caller supplied
 133 **   constant, persistent string of the form name=value. Where
 134 **   name is the name of the environment variable to be set or
 135 **   changed; value is the value assigned to the variable.
 136 **
 137 ** Returns:
 138 **   PRStatus.
 139 **
 140 ** Restrictions:
 141 **   See the Restrictions documented in the description of
 142 **   PR_GetEnv() in this header file.
 143 **
 144 **
 145 */
 146 NSPR_API(PRStatus) PR_SetEnv(const char *string);
 147
 148 /*
 149 ** DEPRECATED.  Use PR_SetEnv() instead.
 150 */
 151 #ifdef XP_MAC
 152 NSPR_API(PRIntn) PR_PutEnv(const char *string);
 153 #endif
 154
 155 PR_END_EXTERN_C
 156
 157 #endif /* prenv_h___ */