Member Function Pointers and Multiple Inheritance
How do we work with member function pointers in the context of multiple inheritance?
Working with member function pointers in the context of multiple inheritance can be a bit tricky, but it's definitely possible. Let's break this down step by step:
Basic Syntax
First, let's recall the basic syntax for a member function pointer:
return_type (ClassName::*pointerName)(parameter_types);Multiple Inheritance Scenario
Now, let's consider a multiple inheritance scenario:
#include <iostream>
class Base1 {
public:
virtual void foo() {
std::cout << "Base1::foo\n";
}
};
class Base2 {
public:
virtual void bar() {
std::cout << "Base2::bar\n";
}
};
class Derived : public Base1, public Base2 {
public:
void foo() override {
std::cout << "Derived::foo\n";
}
void bar() override {
std::cout << "Derived::bar\n";
}
};Pointer to Member Function
To create a pointer to a member function in this context, you need to specify which base class the function belongs to:
#include <iostream>
class Base1 {/*...*/};
class Base2 {/*...*/};
class Derived : Base1, Base2 {/*...*/};
int main() {
void (Base1::*pBase1Foo)() = &Base1::foo;
void (Base2::*pBase2Bar)() = &Base2::bar;
void (Derived::*pDerivedFoo)() = &Derived::foo;
void (Derived::*pDerivedBar)() = &Derived::bar;
}Using the Pointers
To use these pointers, you need an object of the appropriate type:
#include <iostream>
class Base1 {/*...*/};
class Base2 {/*...*/};
class Derived : Base1, Base2 {/*...*/};
int main() {
void (Base1::*pBase1Foo)() = &Base1::foo;
void (Base2::*pBase2Bar)() = &Base2::bar;
void (Derived::*pDerivedFoo)() = &Derived::foo;
void (Derived::*pDerivedBar)() = &Derived::bar;
Derived d;
Base1* pb1 = &d;
Base2* pb2 = &d;
(d.*pDerivedFoo)(); // Calls Derived::foo
(d.*pDerivedBar)(); // Calls Derived::bar
// Calls Derived::foo (virtual dispatch)
(pb1->*pBase1Foo)();
// Calls Derived::bar (virtual dispatch)
(pb2->*pBase2Bar)();
}Derived::foo
Derived::bar
Derived::foo
Derived::barPotential Pitfalls
Be aware of potential pitfalls. Firstly, if both base classes have a function with the same name, you need to explicitly specify which one you're referring to to avoid ambiguity:
void (Derived::*pFoo)() =
static_cast<void (Derived::*)()>(&Base1::foo);Remember that virtual functions will still use dynamic dispatch when called through pointers to member functions.
Additionally, multiple inheritance can lead to the dreaded "diamond problem" if not handled carefully. Always use virtual inheritance when appropriate to avoid this issue.
Using std::function
For more flexibility, you can use std::function along with std::bind:
#include <functional>
#include <iostream>
class Base1 {/*...*/};
class Base2 {/*...*/};
class Derived : Base1, Base2 {/*...*/};
int main() {
Derived d;
std::function<void()> f =
std::bind(&Base1::foo, &d);
f();
}Derived::fooThis approach can make working with member function pointers in multiple inheritance scenarios more manageable.
Remember, while multiple inheritance can be powerful, it also increases complexity. Always consider whether simpler design patterns might achieve your goals more cleanly.
Member Function Pointers and Binding
Explore advanced techniques for working with class member functions