C++ Access member function using pointer

Question

I am not able to access member function using pointer.Find the below code and Error message The Error message is mentioned here error: request for member ‘getstream’ in ‘* objA.A::getfunction()’, which is of non-class type ‘int’ ret = objA.getfunction()->getstream();

#include <iostream>

using namespace std;

class A {
    public: 
    int *getfunction();
    int getstream();
};
int* A::getfunction()
{
      static  int a;
     a= getstream();

    return &a;
}

int getstream()
{
    return 1;
}
int main()
{
int *ret;
A objA;
ret = objA.getfunction()->getstream();
cout << ret;
return 0;
}

Why are you attempting to call `getstream` in the `main` function? Especially considering that you do it using the pointer that `getfunction` is returning (which is a pointer to `int`, i.e. `int*`) which of course doesn't have a `getstream` function. What are you really trying to do? What is supposed to happen in the code? — Some programmer dude, May 16 '20 at 02:53

score 1 · Accepted Answer · answered May 16 '20 at 07:40

If you want to achieve a syntax like objA.getfunction()->getstream(); in your main function, you can do it with class A implementation similar to this :

#include <iostream>

using namespace std;

// class A declaration

class A {

public:
    // Nested class A::AFunction declaration
    class AFunction {
    public:
        int getstream();
    };

private:
    AFunction *p_AFunction;

public:
    A();
    ~A();
    A::AFunction *getfunction();

}; // class A

// class A member function implementations

A::A() : p_AFunction(new AFunction()) {
}

A::~A() {
    delete p_AFunction;
    p_AFunction = nullptr;
}

A::AFunction *A::getfunction() {
    return p_AFunction;
}

// Nested class A::AFunction member function implementations

int A::AFunction::getstream() {
    return 1;
}

// main function

int main() {
    A objA;
    int ret = objA.getfunction()->getstream();
    cout << ret;
    return 0;
}

If you want A::getfunction() function to return a function pointer to a member function in class A, and then invoke it in main function, you can have a implementation similar to this :

#include <iostream>

using namespace std;

// class A declaration

class A {

public:
    typedef int (A::*AMemberFuncPtr) ();

private:
    AMemberFuncPtr fn_getstream;

public:
    A();
    A::AMemberFuncPtr getfunction();

private:
    int getstream();

}; // class A

// class A member function implementations

A::A() : fn_getstream(&A::getstream) {
}

A::AMemberFuncPtr A::getfunction() {
    return fn_getstream;
}

int A::getstream() {
    return 1;
}

// main function

int main() {
    A objA;
    int ret = (objA.*objA.getfunction())();
    cout << ret;
    return 0;
}

Also see the answer to Function pointer to member function.

C++ Access member function using pointer

1 Answers1