C + +: derived class cast to base class

When used in polymorphism, a pointer or reference to a derived class can be converted to a pointer or reference to a base class, where a pointer to a base class can point to the base class part of a derived class;

base* B = derived* D;

B and D point to the same content, b = = d, because there is an implicit conversion between b = = (base*) D;

The addresses of B and d are different int (b)!= int (d), because B points to the base class portion of D, and D points to the complete derived class;

However, if the stealth conversion, int (b)!= int ((base*) d), the address is the same.

The code is as follows:

* * * test.cpp * *  Created on:2014.04.21 * 
 author:spike/
      
/*eclipse CDT, gcc 4.8.1* /
      
#include <iostream>  
      
class A {  
    int m_na;  
};  
      
Class B {  
    int m_nb;  
};  
      
Class C:public A, public B {  
    int m_nc;  
};  
      
int main (void)  
{  
    c* pc = new C;  
    b* PB = pc;  
      
    if (PC = PB) {  
        std::cout << "equal" << Std::endl  
    } else {  
        std::cout << "Not Equal" < < Std::endl;  
    }  
      
    if (int (PC) = = Int (pb)) {  
        std::cout << "equal" << Std::endl;  
    } else {  
        std::cout << "Not E Qual "<< Std::endl;  
    }  
      
    if (int (PC) = = Int ((c*) pb)) {  
        std::cout << "equal" << Std::endl;  
    } else {  
        std::cout << "n OT equal "<< Std::endl;  
    }  
      
    return 0;  
}

Output:

Equal not  
equal  
equal

Author: csdn Blog spike_king

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