Description

   The getpwuid function searches the user database for an entry
   with the specified uid. The function returns the first user entry
   in the database with a pw_uid member of the passwd structure that
   matches the uid argument.

   The passwd structure is defined in the <pwd.h> header file as
   follows:

   pw_name    The user's login name.
   pw_uid     The numerical user ID.
   pw_gid     The numerical group ID.
   pw_dir     The home directory of the user.
   pw_shell   The initial program for the user.

                                  NOTE

      All information generated by the getpwuid function is stored
      in a per-thread static area and is overwritten on subsequent
      calls to the function.

   The getpwuid_r function is the reentrant version of getpwuid.
   The getpwuid_r function updates the passwd structure pointed to
   by pwd and stores a pointer to that structure at the location
   pointed to by result. The structure will contain an entry from
   the user database with a matching uid. Storage referenced by the
   structure is allocated from the memory provided with the buffer
   argument, which is bufsize characters in size. The maximum size
   needed for this buffer can be determined with the _SC_GETPW_R_
   SIZE_MAX parameter of the sysconf function. On error or if the
   requested entry is not found, a NULL pointer is returned at the
   location pointed to by result.

   Applications wishing to check for error situations should set
   errno to 0 before calling getpwuid. If getpwuid returns a NULL
   pointer and errno is nonzero, an error occurred.

   See also getuid to know how UIC is represented.