Enumerating registry values from a key

Multi hours were wasted here because this is about as error prone of an API as you could have. You set max_name_length and max_val_length to tell Windows how big a result you can handle. Fine. But the API then writes back the size it actually needed in those variables. Then, the next time around those values are likely too small, leading to an ERROR_MORE_DATA return value. Sigh.

In this example I've got a dedicated key with values with meaninglesss value names...I just want the value values, each stuffed into an element in a 2D array.

Note that I believe you need to have the 2 index vars as shown, because of the way Windows stores these things.

   my_roots[0][0] = 0;
   LONG result = ERROR_SUCCESS;
   while (result != ERROR_NO_MORE_ITEMS)
   {
      max_name_length = 10;
      max_val_length = MAX_PATH;
      result =
         RegEnumValue(dirKeyHandle, reg_index, this_name, &max_name_length, NULL, &type, (unsigned char*)&my_roots[array_index][0], &max_val_length);
      reg_index++;
      if (result == ERROR_SUCCESS)
      {   array_index++;
      }
   }

A generic example

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
    char keyName[] = "SOFTWARE\\SomeKey";
    DWORD whatHappened; // designates whether key created & opened or existing key opened

    /* open key, create new one if non-existent
     */
    result = RegCreateKeyEx(HKEY_LOCAL_MACHINE, keyName, 0, "dontcare", REG_OPTION_NON_VOLATILE,
      KEY_ALL_ACCESS, 0, &keyHandle, &whatHappened);

    if (result != ERROR_SUCCESS)   
    {
        MessageBox(NULL,"Can't make registry changes", "Hosed", MB_OK); 
        return 1;
    }

    /* Set a DWORD value
     */
    DWORD theData = 0x01;

    result = RegSetValueEx(keyHandle, "ValueName", 0, REG_DWORD, (LPBYTE)&theData, 4);
    if (result != ERROR_SUCCESS)   
    {
        MessageBox(NULL,"Can't make registry changes", "Hosed", MB_OK); 
        return 1;
    }
    
    RegCloseKey(keyHandle);
    return 0;
}

-- MattWalsh - 08 Nov 2002