pointers - C++ types of casting, what they're doing, and which variables are valid? -

this question has answer here:

• regular cast vs. static_cast vs. dynamic_cast [duplicate] 8 answers
• when should static_cast, dynamic_cast, const_cast , reinterpret_cast used? 6 answers

ok i'm having trouble understanding different types of casting , whats going on them. created 2 classes: , b. b derived a.

i made bunch of pointers , dumb them screen. need understanding what's going on , variables valid.

here's code:

#include <iostream>  using namespace std;   class { public:     a(int ivalue){             m_ivalue = ivalue;     }      a(){             m_ivalue = 10;     }      virtual void dosomething(){             cout << "the value " << getvalue() << endl;     }      void dosomethingelse(){             cout << "this else" << endl;     }      virtual int getvalue(){             return m_ivalue;     }  private:     int m_ivalue; };  class b : public a{  public:  b() : a(5){      }      virtual void dosomething(){              cout << "this time, value " << getvalue() << endl;     }      void dosomethingelse(){              cout << "this else entirely" << endl;     }      virtual void doanotherthing(){              cout << "and third thing" << endl;     } };   int main(int argc, char * argv[]){     * pa1 = new b;     * pa2 = new a;      b * pb1;     b * pb2;      pb1 = (b*)pa1;     pb2 = (b*)pa2;      cout << "step 1 - c style cast:" << endl;     cout << "  pa1 cast pointer pb1: " << pb1 << endl;     cout << "  pa2 cast pointer pb2: " << pb2 << endl << endl;      b * pb3;     b * pb4;      pb3 = dynamic_cast<b*>(pa1);     pb4 = dynamic_cast<b*>(pa2);      cout << "step 2 - dynamic_cast:" << endl;     cout << "  pa1 cast pointer pb3: " << pb3 << endl;     cout << "  pa2 cast pointer pb4: " << pb4 << endl << endl;       b * pb5;     b * pb6;      pb5 = static_cast<b*>(pa1);     pb6 = static_cast<b*>(pa2);      cout << "step 3 - static_cast:" << endl;     cout << "  pa1 cast pointer pb5: " << pb5 << endl;     cout << "  pa2 cast pointer pb6: " << pb6 << endl << endl;      b * pb7;     b * pb8;      pb7 = reinterpret_cast<b*>(pa1);     pb8 = reinterpret_cast<b*>(pa2);      cout << "step 4 - reinterpret_cast:" << endl;     cout << "  pa1 cast pointer pb7: " << pb7 << endl;     cout << "  pa2 cast pointer pb8: " << pb8 << endl << endl;      return 0; } 

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here's outputs:

step 1 - c style cast:   pa1 cast pointer pb1: 0x1853010   pa2 cast pointer pb2: 0x1853030  step 2 - dynamic_cast:   pa1 cast pointer pb3: 0x1853010   pa2 cast pointer pb4: 0  step 3 - static_cast:   pa1 cast pointer pb5: 0x1853010   pa2 cast pointer pb6: 0x1853030  step 4 - reinterpret_cast:   pa1 cast pointer pb7: 0x1853010   pa2 cast pointer pb8: 0x1853030