operator []重载以接受char *作为下标

Question

I have following code:

class IList{
public:
    virtual const Pair *get(const char *key) const = 0;

    inline const Pair *operator[](const char *key) const;
};

inline const Pair *IROList::operator[](const char *key) const{
    return get(key);
}

code compiles ok, but when I try to use it:

IList *list = (IList *) SomeFactory();
Pair *p;
p = list["3 city"];

I got:

test_list.cc:47:19: error: invalid types ‘IList*[const char [7]]’ for array subscript
  p = list["3 city"];
                   ^

I can understand that array subscript is int or char, but then how std::map is doing char* / strings ?

Answer 1

If your list is a pointer as well you can't use [] operator in the way you did. That's because list["3 city"] is equivalent to list.operator[]("3 city") . If you provide pointer, you'd have to use list->operator[]("3 city") or - what is more readable - (*list)["3 city"] . Of course, you can also make your list a reference and use normally:

auto& listRef = *list;
p = listRef["3 city"];

Answer 2

It seems list is a pointer to IList object. So you should try: p = (*list)["3 city"];