Get C++ virtual function table address and virtual function address

1. First introduce the memory structure of C++ class, you can read the following blog, feel good

　　https://blog.csdn.net/fenxinzi557/article/details/51995911

　　The knowledge point related to this time is that the first 4 bytes of a class with virtual functions are pointers to the first address of the virtual function table _vfptr

2. Let's start with the specific solution process

class  AA {  
public:  
    virtual void func1() { cout << "AA ::func1" << endl; }  
    virtual void func2() { cout << "AA ::func2" << endl; }  
    void func3() { cout << "AA::func3" << endl; }  
};  
  
typedef void(*Fun)(void); //function pointer  
intmain()  
{  
    AA a;  
    // *****printf("Virtual table address:%p\n", *(int *)&a); Parse *****:  
    // 1.&a represents the starting address of object a  
    // 2. (int *)&a is cast to int * type, in order to take the first four bytes of the a object later, the first four bytes are the virtual table pointer  
    // 3.*(int *)&a Take the first four bytes, which is the address of the vptr virtual table  
    
  
    // *****printf("First virtual function address: %p\n", *(int *)*(int *)&a);*****:  
    // According to the above analysis, we know that *(int *)&a is vfptr, the virtual table pointer. And the virtual table stores virtual function pointers  
    // So each element (virtual function pointer) in the virtual table is 4 bytes under a 32-bit compiler, so (int *)*(int *)&a
    // After such a strong conversion, four bytes are taken for the following. So *(int *)*(int *)&a is the first element of the virtual table.  
    // That is the address of f().  
    // Then take the second virtual function address and so on. Always remember that vfptr points to a piece of memory,  
    // This piece of memory stores the virtual function address, this piece of memory is what we call the virtual table.  
    //  
    printf("Address of virtual table:%p\n", *(int *)&a);  
    printf("First virtual function address: %p\n", *(int *)*(int *)&a);  
    printf("Second virtual function address: %p\n", *((int *)*(int *)(&a) + 1));  
  
    Fun pfun = (Fun)*((int *)*(int *)(&a));  //virtual func1();  
    printf("func1():%p\n", pfun);  
    pounds();  
  
    pfun = (Fun)(*((int *)*(int *)(&a) + 1));  //virtual func2();  
    printf("func2():%p\n", pfun);  
    pounds();  
  
}