nsresult rv;
NS_IMETHODIMP nsPref::CopyUnicharPref(const char *pref, PRUnichar **_retval){  nsresult rv;  nsCOMPtr<nsIPrefBranch> prefBranch = do_QueryInterface(mPrefService, &rv);  if (NS_SUCCEEDED(rv)) {    nsCOMPtr<nsISupportsWString> theString;    rv = prefBranch->GetComplexValue(pref, NS_GET_IID(nsISupportsWString),                                     getter_AddRefs(theString));    if (NS_SUCCEEDED(rv)) {      rv = theString->GetData(_retval);    }  }  return rv;}