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 29.11 Identifying Who Logged In
 ===============================
 
 You can use the functions listed in this section to determine the login
 name of the user who is running a process, and the name of the user who
 logged in the current session.  See also the function `getuid' and
 friends ( Reading Persona).  How this information is collected by
 the system and how to control/add/remove information from the background
 storage is described in  User Accounting Database.
 
    The `getlogin' function is declared in `unistd.h', while `cuserid'
 and `L_cuserid' are declared in `stdio.h'.  
 
  -- Function: char * getlogin (void)
      The `getlogin' function returns a pointer to a string containing
      the name of the user logged in on the controlling terminal of the
      process, or a null pointer if this information cannot be
      determined.  The string is statically allocated and might be
      overwritten on subsequent calls to this function or to `cuserid'.
 
  -- Function: char * cuserid (char *STRING)
      The `cuserid' function returns a pointer to a string containing a
      user name associated with the effective ID of the process.  If
      STRING is not a null pointer, it should be an array that can hold
      at least `L_cuserid' characters; the string is returned in this
      array.  Otherwise, a pointer to a string in a static area is
      returned.  This string is statically allocated and might be
      overwritten on subsequent calls to this function or to `getlogin'.
 
      The use of this function is deprecated since it is marked to be
      withdrawn in XPG4.2 and has already been removed from newer
      revisions of POSIX.1.
 
  -- Macro: int L_cuserid
      An integer constant that indicates how long an array you might
      need to store a user name.
 
    These functions let your program identify positively the user who is
 running or the user who logged in this session.  (These can differ when
 setuid programs are involved; see  Process Persona.)  The user
 cannot do anything to fool these functions.
 
    For most purposes, it is more useful to use the environment variable
 `LOGNAME' to find out who the user is.  This is more flexible precisely
 because the user can set `LOGNAME' arbitrarily.   Standard
 Environment.
 

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