struct Login {
             QString userName;
             QString password;
         };
         QList<Login> logins;
         ...

         QSettings settings;
         settings.beginWriteArray("logins");
         for (int i = 0; i < logins.size(); ++i) {
             settings.setArrayIndex(i);
             settings.setValue("userName", list.at(i).userName);
             settings.setValue("password", list.at(i).password);
         }
         settings.endArray();