enum initialization issue

Here is a sample program :

class BASE
{
        public:
        enum ABC
        {
                ZERO,
     开发者_Python百科           ONE,
                TWO,
                LAST
        };
        BASE(ABC exp): type(exp)
        {
                A[ZERO] = "1111";
               A[ONE] = "22222";
                A[LAST] = "LLLL";
        }
        virtual const char* what()throw()
        {
               return A[type];
        }
        private:
        const char* A[LAST];
        const ABC type;
};

int main()
{
        BASE a(BASE::ONE);
        cout<<a.what()<<"\n";
        return 0;
}

The above program terminates with segmentation fault, as 'type' enum variable is not initialized with specified value but with some random default ?

A is an array of three pointers, A[0], A[1], and A[2].

You have a pointer to "LLLL" which is OK. But when you try to assign that pointer to A[3], there is no such object as A[3].

You declare the array A as

const char* A[LAST];

This means that the indices 0 .. (LAST-1) are all valid. However, in the BASE constructor you perform

 A[LAST] = "LLLL";

This is an out-of-bounds access to the array.

If you want a "LAST" entry, try this:

 enum ABC
 {
     ZERO,
     ONE,
     TWO,
     LAST = TWO
 };