开关盒的多种情况？

Question

我可以使用开关盒来检查多种情况吗？例如,无论是其中任何一个条件还是满足条件,它都会做到这一点？

switch (conditionA or conditionB fullfilled)
  { //execute code }

Answer 1

显然,如果条件A或条件B是如何执行代码的问题true可以简单地回答if( conditionA || conditionB ),没有switch必要的声明.如果一个switch声明出于某种原因是必须的,那么通过建议一个case标签可以通过其他答案之一来解决这个问题,可以再简单地回答这个问题.

我不知道OP的需求是否完全由这些微不足道的答案所涵盖,但是除了OP之外,很多人都会阅读这个问题,所以我想提出一个更通用的解决方案,它可以解决许多类似的问题答案根本不会做.

如何使用单个switch语句同时检查任意数量的布尔条件的值.

这很hacky,但它可能会派上用场.

关键是要在转换true/ false您的每一个条件的值了一下,这些位连接成一个int值,然后switch在int值.

这是一些示例代码:

#define A_BIT (1 << 0)
#define B_BIT (1 << 1)
#define C_BIT (1 << 2)

switch( (conditionA? A_BIT : 0) | (conditionB? B_BIT : 0) | (conditionC? C_BIT : 0) )
{
     case 0:                     //none of the conditions holds true.
     case A_BIT:                 //condition A is true, everything else is false.
     case B_BIT:                 //condition B is true, everything else is false.
     case A_BIT + B_BIT:         //conditions A and B are true, C is false.
     case C_BIT:                 //condition C is true, everything else is false.
     case A_BIT + C_BIT:         //conditions A and C are true, B is false.
     case B_BIT + C_BIT:         //conditions B and C are true, A is false.
     case A_BIT + B_BIT + C_BIT: //all conditions are true.
     default: assert( FALSE );   //something went wrong with the bits.
}

然后,case如果您有一个或多个方案,则可以使用标签.例如:

switch( (conditionA? A_BIT : 0) | (conditionB? B_BIT : 0) | (conditionC? C_BIT : 0) )
{
     case 0:
         //none of the conditions is true.
         break;
     case A_BIT:
     case B_BIT:
     case A_BIT + B_BIT:
         //(either conditionA or conditionB is true,) and conditionC is false.
         break;
     case C_BIT:
         //condition C is true, everything else is false.
         break;
     case A_BIT + C_BIT:
     case B_BIT + C_BIT:
     case A_BIT + B_BIT + C_BIT:
         //(either conditionA or conditionB is true,) and conditionC is true.
         break;
     default: assert( FALSE );   //something went wrong with the bits.
}

.

Answer 2

不可以.在c ++中,switch case只能用于检查一个变量的值是否相等:

switch (var) {
    case value1: /* ... */ break;
    case value2: /* ... */ break;
    /* ... */
}

但您可以使用多个开关:

switch (var1) {
    case value1_1:
        switch (var2) {
            /* ... */
        }
        break;
    /* ... */
}

Answer 3

开关/外壳结构的跌落功能怎么样？

switch(condition){
    case case1:
        // do action for case1
        break;
    case case2:
    case case3:
        // do common action for cases 2 and 3
        break;
    default:
        break;
}