使用const指针或指针作为`std :: map`的键

Question

#include <map>

class ClassOne
{
   //...
};

int main() {
    std::map< ClassOne *, int >             mapA;
    std::map< const ClassOne *, int >       mapB;
    std::map< ClassOne *const, int >        mapC;
    std::map< const ClassOne * const, int > mapD;

    return 0;
}

Question> I need to use address of ClassOne as the key for std::map . which one is the best choice?

Thank you

Answer 1

This depends on what you actually want to do -- however, you seldom want to change keys, so ClassOne * const if you're not intending to change the pointer ; if you don't want to change the object that pointer points to, const ClassOne * const .