C/C++黑魔法-另类switch

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介绍duff写法与范围判断

duff写法

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int n = 1;
switch (n) {
    case 0: do { printf("%d ", 0);
    case 1: printf("%d ", 1);
    case 2: printf("%d ", 2);
    case 3: printf("%d ", 3);
    case 4: printf("%d ", 4);
            } while (n-- > 0);
}
  • 用于循环优化，提高性能。但现代编译器已经支持得很好了。
  • 输出
    1
    1 2 3 4 0 1 2 3 4

范围判断

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int i = 5;
switch (i) {
    case 0 ... 3:
        std::cout<<"0-3: "<<i<<std::endl;
        break;
    case 4 ... 6:
        std::cout<<"4-6: "<<i<<std::endl;
        break;
    case 7 ... 9:
        std::cout<<"7-9: "<<i<<std::endl;
        break;
    case 10:
        std::cout<<"10"<<i<<std::endl;
    default:
        break;
}
  • 注意: gnu编译器，mingw编译器支持
  • 输出
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    4-6: 5