Question

我正在实施串行通信协议。在这个实现的接收函数中，我有多个出口点，带有重复的代码用于清理。在结构/ OO编程语言的情况下，我不确定表达式SESE是否有效。我正在使用C ++。这不是MCVE，而只是我在代码中的结构。代码看起来像：

bool receive()
{
  bool status = false;
  initializeCommunication();
  if (receiveOneByteIsNotWhatExpected())
  {
     cleanupCode();
     return status;
  }
  processFirstParam();
  if (receiveTwoBytesIsNotWhatExpected())
  {
    cleanupCode();
    return status;
  }
  processSecondParam();
  if (receiveOneByteIsNotWhatExpected())
  {
    cleanupCode();
    return status;
  }
  processThirdParam();
  if (receiveFourBytesIsNotWhatExpected())
  {
    cleanupCode();
    return status;
  }
  processFourthParam();
  status = true;
  cleanupCode();
  return status;
}

我想重构它。一种方法是使用一种状态机，例如：

bool receive()
{
  status = true;
  state = START;
  while (status && state != POSTENDED)
  {
    switch(state)
    {
      case START:
        initializeCommunication();
        state = RECEIVEFIRSTONEBYTE;
        // fall-through
      case RECEIVEFIRSTONEBYTE:
        if (receiveOneByteIsNotWhatExpected())
        {
          status = false;
        }
        else
        {
          processFirstParam();
          state = RECEIVESECONDTWOBYTES;
        }
          break;
      case RECEIVESECONDTWOBYTES:
       if (receiveTwoBytesIsNotWhatExpected())
       {
         status = false;
       }
       else
       {
         processSecondParam();
         state = RECEIVETHIRDONEBYTE:
       }
       break;
       case RECEIVETHIRDONEBYTE:
        if (receiveOneByteIsNotWhatExpected())
        {
          status = false;
        }
        else
        {
          processThirdParam();
          state = RECEIVEFOURTHFOURBYTES;
        }
        break;
        case RECEIVEFOURTHFOURBYTES:
        if (receiveFourBytesIsNotWhatExpected())
        {
          status = false;
        }
        else
        {
          processFourthParam();
          state = ENDED;
        }
        break;
        case ENDED:
          status = true;
          state = POSTENDED;
        break;
    }
  }
  cleanupCode();
  return status;
}

编写上述代码的第三种方法是使用嵌套的if语句，它将生成嵌套if语句的四个级别，但这将是简洁的。编写这种代码的优化方法是什么，以及每种代码的优缺点是什么。

Answer 1

虽然标签和goto的使用通常不受欢迎，但这通常是许多人认为可以使用的情况之一。

所以没有例如。

if (receiveOneByteIsNotWhatExpected())
{
  cleanupCode();
  return status;
}
...

你会有像

这样的东西

if (receiveOneByteIsNotWhatExpected())
{
  goto end;
}

在功能结束时：

  processFourthParam();
  status = true;
end:
  cleanupCode();
  return status;
}

这将最大限度地减少公共代码的重复，并且是“一次退货”或“单一进入，单一退出”原则的基石。

Answer 2

清理守卫怎么样：

SELECT EMPID
FROM yourTable
GROUP BY EMPID
HAVING SUM(CASE WHEN Status NOT IN ('A', 'B') OR Status IS NULL THEN 1 ELSE 0 END) = 0 AND
       COUNT(DISTINCT Status) = 2

内联函数：

bool receive()
{
    bool status = false;
    initializeCommunication();
    struct CleanupGuard
    {
        ~CleanupGuard()
        {
           cleanupCode();
        }
    } g;
    if (receiveOneByteIsNotWhatExpected())
    {
        return status;
    }
    // [...]
}

循环方式：

namespace
{
   inline bool doReceive()
   {
       // [...]
   }
}

bool receive()
{
    initializeCommunication();
    bool status = doReceive();
    cleanupCode();
    return status;
}

使用清理代码优化多个出口点

2 个答案: