預設

在 switch 語句中，如果條件的值不等於任何 case 標籤的值，則引入將跳轉到的標籤。

char c = getchar();
bool confirmed;
switch (c) {
  case 'y':
    confirmed = true;
    break;
  case 'n':
    confirmed = false;
    break;
  default:
    std::cout << "invalid response!\n";
    abort();
}

Version >= C++ 11

定義預設建構函式，複製建構函式，移動建構函式，解構函式，複製賦值運算子或移動賦值運算子以使其具有預設行為。

class Base {
    // ...
    // we want to be able to delete derived classes through Base*,
    // but have the usual behaviour for Base's destructor.
    virtual ~Base() = default;
};