为什么不能增加枚举类型的变量？ [英] Why can't I increment a variable of an enumerated type?

问题描述

我有一个枚举类型 StackID ，我使用枚举来引用特定向量的索引，它使我的代码更容易阅读。

但是，现在我需要创建一个 nextAvail 变量 StackID 。 （它实际上是指一个特定的stackID）。我试图增加它，但在C ++，以下是非法的：

  nextAvail ++; 
  

对我来说有什么意义...因为没有边界检查。

$

---

我可能会忽略某些明显的东西，我还想链接到此问题。

解决方案

我可能忽略了一些明显的东西，但什么是好的替代品？

重载运算符++ ：

  //小心，大脑编译代码！ 
 StackID& operator ++（StackID& stackID）
 {
 #if MY_ENUMS_ARE_CONTIGUOUS&& I_DO_NOT_WORRY_ABOUT_OVERFLOW 
 return stackID = static_cast< StackID>（++ static_cast< int>（stackID））; 
 #else 
 switch（stackID）{
 case value1：return stackID = value2; 
 case value2：return stackID = value3; 
 ... 
 case valueN：return stackID = value1; 
} 
 assert（false）; 
 return stackID; //一些编译器可能会警告否则
 #endif 
} 
 
 StackID运算符++（StackID& stackID，int）
 {
 StackID tmp（stackID）; 
 ++ stackID; 
 return tmp; 
} 
  

I have a enumerated type StackID, and I am using the enumeration to refer to an index of a particular vector and it makes my code easier to read.

However, I now have the need to create a variable called nextAvail of type StackID. (it actually refers to a particular stackID ). I tried to increment it but in C++, the following is illegal:

nextAvail++;

Which sort of makes sense to me ... because there's no bounds checking.

I'm probably overlooking something obvious, but what's a good substitute?

---

I also want to link to this question.

解决方案

I'm probably overlooking something obvious, but what's a good substitute?

Overloading operator++:

// Beware, brain-compiled code ahead! 
StackID& operator++(StackID& stackID)
{
#if MY_ENUMS_ARE_CONTIGUOUS && I_DO_NOT_WORRY_ABOUT_OVERFLOW
  return stackID = static_cast<StackID>( ++static_cast<int>(stackID) );
#else
  switch(stackID) {
    case value1 : return stackID = value2;
    case value2 : return stackID = value3;
    ...
    case valueN : return stackID = value1;
  }
  assert(false);
  return stackID; // some compilers might warn otherwise
#endif
}

StackID operator++(StackID& stackID, int)
{
  StackID tmp(stackID);
  ++stackID;
  return tmp;
}

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