[C++] Pointer to function giving error

I have a very simple function pointer that I even got out of a book, but my compiler (dev cpp) is giving me the following errors:

35 C:\Dev-Cpp\main.cpp invalid use of non-static member function `virtual void Mammal::speak()'

35 C:\Dev-Cpp\main.cpp cannot convert `void (Mammal::)()' to `void (Mammal::*)()' in assignment


The code is as follows:

Code:

---

#include <iostream>
using namespace std;

class Mammal
{
  public:
        Mammal() { }
        virtual ~Mammal() { }
        Mammal(const Mammal&) { }
       
        virtual void speak()
        {
            cout << "Mammal speak\n";
        }
};

class Cat: public Mammal
{
      public:
            Cat() { }
            ~Cat() { }
            Cat(const Cat&) { }
           
            void speak()
            {
              cout << "Meow\n";
            }
};


int main(int argc, char* argv[])
{
    Mammal m;
    void (Mammal::*pFunc)() = 0;
    pFunc = Mammal::speak;
   
    Mammal* ptr = new Cat;
    (ptr->*pFunc)();
   
    delete ptr; 
}

---

What exactly am I doing wrong to recieve this error? Everything looks correct?

I think you just need to add the 'address of' operator in front of Mammal:

Code:

---

    pFunc = &Mammal::speak;

---

HTH!

You cant use function pointers for member functions (non static) as you do with common functions. It needs a special declaration and you must involve an instance of the object to call them.

Quote:

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Originally Posted by bilm_ks

You cant use function pointers for member functions (non static) as you do with common functions. It needs a special declaration and you must involve an instance of the object to call them.

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My book says you can :)

Quote:

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I think you just need to add the 'address of' operator in front of Mammal:

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That's it sunburt! I'm thinking certain compilers actually accept the form without the address of operator.

Thanks.

Quote:

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Originally Posted by bilm_ks

You cant use function pointers for member functions (non static) as you do with common functions. It needs a special declaration and you must involve an instance of the object to call them.

---

The code System_Error posted has both the special declaration and an instance which invokes the function -- so you're right, but uneccesary :p


I think that when taking the address of a non-static member function, that the & is necessary. I know that with regular (non-class) functions, the & is optional.

Correct. Basically, the form without the & was kept for C compatibility, but disliked, so when it came to member functions, where C compatibility was not an issue, so the & was made mandatory.