从指针访问[]运算符 [英] Accessing the [] operator from a pointer

问题描述

如果我定义了指向定义[]运算符的对象的指针，是否有直接方法可以从指针访问该运算符?

If I define a pointer to an object that defines the [] operator, is there a direct way to access this operator from a pointer?

例如，在下面的代码中，我可以使用指针的->运算符直接访问Vec的成员函数(例如empty())，但是如果要访问[]运算符，我需要首先获取对该对象的引用，然后调用操作符.

For example, in the following code I can directly access Vec's member functions (such as empty()) by using the pointer's -> operator, but if I want to access the [] operator I need to first get a reference to the object and then call the operator.

#include <vector>

int main(int argc, char *argv[])
{
    std::vector<int> Vec(1,1);
    std::vector<int>* VecPtr = &Vec;

if(!VecPtr->empty())      // this is fine
    return (*VecPtr)[0]; // is there some sort of ->[] operator I could use?

return 0;
}

我很可能是错的，但是看起来执行(*VecPtr).empty()的效率要比执行VecPtr->empty()的效率低.这就是为什么我要寻找(*VecPtr)[]的替代品.

I might very well be wrong, but it looks like doing (*VecPtr).empty() is less efficient than doing VecPtr->empty(). Which is why I was looking for an alternative to (*VecPtr)[].

推荐答案

您可以执行以下任一操作:

You could do any of the following:

#include <vector>

int main () {
  std::vector<int> v(1,1);
  std::vector<int>* p = &v;

  p->operator[](0);
  (*p)[0];
  p[0][0];
}

顺便说一句，在std::vector的特殊情况下，您可能还会选择:p->at(0)，即使它的含义稍有不同.

By the way, in the particular case of std::vector, you might also choose: p->at(0), even though it has a slightly different meaning.

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