int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer,
       size_t bufsize, struct passwd **result);

long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
       size_t len;
       if (initlen == −1)
           /* Default initial length. */
           len = 1024;
       else
           len = (size_t) initlen;
       struct passwd result;
       struct passwd *resultp;
       char *buffer = malloc(len);
       if (buffer == NULL)
           ...handle error...
       int e;
       while ((e = getpwuid_r(42, &result, buffer, len, &resultp)) == ERANGE)
           {
           size_t newlen = 2 * len;
           if (newlen < len)
               ...handle error...
           len = newlen;
           char *newbuffer = realloc(buffer, len);
           if (newbuffer == NULL)
               ...handle error...
           buffer = newbuffer;
           }
       if (e != 0)
           ...handle error...
       free (buffer);