C++: Store & Call the function pointers in a vector of function pointers

Question

I've a scenario as below code. I'm trying to

Store the address of a C++ member function in a vector of function pointers.
access a C++ member function using this vector of function pointers.

I am able to add the functions, but I can't call them. The error I get is:

error: must use '.' or '->' to call pointer-to-member function in

class allFuncs {
     private:
        std::vector<void *(allFuncs::*)(int)> fp_list; // Vector of function pointers

       void func_1(int a) {
           // some code
        }

       void func_2(int a) {
           // some code
        }

        void func_3() {
           // STORING THE FUNCTION POINTER INTO The VECTOR OF FUNCTION POINTERS
           fp_list.push_back(&func_2);
           fp_list.push_back(allFuncs::func_1);      
        }

        func_4() {
          // Calling the function through the function pointer in vector
          this->*fp_list.at(0)(100);  // this does not work 
        }
}

Also see: https://stackoverflow.com/questions/30573184/vector-of-pointers-to-member-functions-with-multiple-objects-c — NathanOliver, May 06 '20 at 19:12
@NathanOliver: Updated with proper syntax for declaring vector of function pointers but I'm facing issues while calling the function pointer using the syntax: (I've updated in the code. this->*fp_list.at(0)(100); — codeLover, May 06 '20 at 19:43
I believe you need another set of parentheses: `this->*(fp_list.at(0))(100);` — NathanOliver, May 06 '20 at 19:45
Tried this too actually but same error & cribbing for "error: must use '.' or '->' to call pointer-to-member function in" — codeLover, May 06 '20 at 19:48
OK. I've edit the Q to make the calling syntax the actual question and reopened it. I know the syntax is really funky, I just can't remember it. — NathanOliver, May 06 '20 at 19:50
Awesome (this->*fp_list.at(0))(100) worked. I wonder how does this outer parenthesis make a difference. — codeLover, May 06 '20 at 20:14

score 1 · Answer 1 · edited May 07 '20 at 06:14

You need to use

(this->*fp_list.at(0))(100)

to call the function from the vector. When you do

this->*fp_list.at(0)(100)

The function call (the (100) part) is bound to fp_list.at(0) so basically you have

this->*(fp_list.at(0)(100))

which won't work. Adding parentheses around the function pointer access fixes that so this->*fp_list.at(0) becomes the function to call and then the (100) is used on that function.

C++: Store & Call the function pointers in a vector of function pointers

1 Answers1