函數指針

（1/2）類型 

普通函數指針不能被賦值為成員函數的地址。

int (*pFunc)();

pFunc是一個函數指針，而int (*)()是類型。

成員函數地址要賦值給成員函數指針。

class Base
{
public:
    int func() { return 1; }
};

int main()
{
    int (*pFunc)();
    pFunc = &Base::func;  //error: cannot convert 'int (Base::*)()' to 'int (*)()' in assignment
    return 0;
}

class Base
{
public:
    int func() { return 1; }
};

int main()
{
    int (Base::*pFunc)(); // OK
    pFunc = &Base::func;
    return 0;
}

再來：

class Base
{
public:
    int func() { return 1; }
};
class Derived : public Base
{
public:
    int foo() { return 1; }
};

int main()
{
    typedef int (Base::*FuncPtr)();
    FuncPtr fPtr = &Derived::foo; // error
    return 0;
}

需進行強制類型轉換

......

FuncPtr fPtr = (FuncPtr)&Derived::foo;  // OK

反過來，基類成員函數地址可賦值給指向派生類成員函數的指針。

class Base
{
public:
    int func() { return 1; }
};
class Derived : public Base
{
public:
    int foo() { return 1; }
};

int main()
{
    typedef int (Derived::*FuncPtr)();
    FuncPtr fPtr = &Base::func;  // OK
    return 0;
}

（2/2）調用

class Base
{
public:
    virtual void func(int i) { cout << "Base: " << i << endl; }
};
class Derived : public Base
{
public:
    virtual void func(int i) { cout << "Derived: " << i << endl; }
};

int main()
{
    typedef void (Base::*FuncPtr)(int);
    FuncPtr fPtr = &Base::func;
    Base b;
    (b.*fPtr)(2);
    Derived* dPtr = new Derived();
    (dPtr->*fPtr)(2);
    Base* bPtr = new Derived();
    (bPtr->*fPtr)(2);
    return 0;
}

output:

Base: 2
Derived: 2
Derived: 2