Using a function pointer array to call a method of a class - c++

Question

I would like to write a program in C++ which contains an array of function pointers.
Here is the code:
#include <iostream>
using namespace std;
class MyClass {
int a, b;
public:
MyClass(int i, int j) : a(i), b(j) {}
int add() { return a + b; }
int sub() { return a - b; }
};
void func(int (MyClass::* funcPtr[])(), MyClass& a, int i) {
if (i == 0) {
funcPtr[i] = &MyClass::add;
funcPtr;
}
if (i == 1) {
funcPtr[i] = &MyClass::sub;
funcPtr;
}
cout << " Result: " << (a.*funcPtr[i])() << endl;
}
int main(){
int auswahl = 0;
int i = 4, j = 5;
cout << "Which function? [0]-Add [1]-Substract\n";
cin >> select;
MyClass a(i,j);
func(NULL, a, select);
}
After playing around a lot I got the program to compile successfully. But it throws "Write Access Violation" on running.
The problem seems to be related to:
funcPtr[i] = &MyClass::add;
funcPtr[i] = &MyClass::sub;
It'd be very nice, if you could help me solve the problem.
Thank you so much and have a happy time!

Answer 1

As you pass NULL or nullptr in your function, so this line:
funcPtr[i] = &MyClass::add;
Is writing at index i into a null array!
You'd have to provide an array for your function to write into:
MyClass a(i,j);
int (MyClass::* funcPtr[2])();
func(funcPtr, a, select);
Note that using std::array instead of c-style array would avoid this problem, since they are not nullable:
void func(std::array<int (MyClass::*)(), 2> funcPtr, MyClass& a, int i) {
// ...
}
// ...
std::array<int (MyClass::*)(), 2> funcPtr;
func(funcPtr /* cannot pass null */, a, i);