C ++ type conversion dynamic_cast Parsing

C ++ type conversion dynamic_cast Parsing

There are four types of C ++ conversions: const_cast, reinterpret_cast, static_cast, and dynamic cast.

Here is a small example of dynamic cast.

# Include
 
  
Using namespace std; class BaseClass {public: int m_iNum; virtual void foo () {}; // The base class must have virtual functions. Dynamic_cast}; class DerivedClass: public BaseClass {public: char * m_szName; DerivedClass (char * str) {m_szName = new char [strlen (str) + 1]; strcpy (m_szName, str );}~ DerivedClass () {if (m_szName! = NULL) {delete [] m_szName; m_szName = NULL ;}} void bar () {};}; int main () {// 64-bit system, int: 4, vtable_prt: the output value of 8 is 16 cout <"sizeof (BaseClass) =" <sizeof (BaseClass) <endl; // 64-bit system, 4 + 8 + 8 = 24 cout <"sizeof (DerivedClass) =" <sizeof (DerivedClass) <endl; char * p = "abc "; baseClass * pb = new DerivedClass (p); cout <"sizeof (* pb):" <sizeof (* pb) <endl; // 16 DerivedClass * pd1 = static_cast
  
   
(Pb); // subclass-> parent class, static type conversion, correct, but not recommended DerivedClass * pd2 = dynamic_cast
   
    
(Pb); // subclass-> parent class, dynamic type conversion, correct cout <pd1-> m_szName <endl; // abc cout <pd2-> m_szName <endl; // abc cout <"sizeof (* pd1):" <sizeof (* pb) <endl; // 16 cout <"sizeof (* pd2):" <sizeof (* pb) <endl; // 16 BaseClass * PBS = new BaseClass (); derivedClass * pd21 = static_cast
    
     
(PBS); // parent class-> subclass, static type conversion, dangerous! Access subclass m_szName member out of bounds DerivedClass * pd22 = dynamic_cast
     
      
(); // Parent class-> subclass, dynamic type conversion, secure. The result is NULL cout <"sizeof (* pd21):" <sizeof (* pb) <endl; // 16 cout <"sizeof (* pd22 ): "<sizeof (* pb) <endl; // 16 cout <pd21 <
      
        M_szName indicates segmentation fault cout <pd22 <
       
        
Output result:
        

        

        
sizeof(BaseClass) = 16sizeof(DerivedClass) = 24sizeof(*pb): 16abcabcsizeof(*pd1): 16sizeof(*pd2): 160x7f9a7b403a600sizeof(*pd21): 16sizeof(*pd22): 16