c++ - pointer problems with inherited class -


in below code secclass inheriting 'item' firstclass. when run 'classc' in main both first item , second item 210. if remove pointer inherited class(firstclass), runs should. i'm still rather shaky both pointers , inheritance there's i'm missing here...

// declaration of firstclass // firstclass.h  #include <iostream>  #ifndef firstclass_h #define firstclass_h  using namespace std;  class firstclass {  private:    int *item;   public:    firstclass();    firstclass(int thatitem);    ~firstclass();     int getitem();    void setitem(int thatitem);  };  #endif   // implementation of firstclass.h // firstclass.cpp  #include "firstclass.h"  using namespace std;  firstclass::firstclass() {  int *setinitial = new int; *setinitial = 5; item = setinitial; }  firstclass::firstclass(int thatitem) { item = &thatitem; }  firstclass::~firstclass(){}  int firstclass::getitem() {     return *item; }  void firstclass::setitem(int thatitem)  {     item = &thatitem; }   // declaration of secclass // secclass.h  #ifndef secclass_h #define secclass_h  #include "firstclass.h"  using namespace std;  class secclass : public firstclass {  private:    int *secitem;   public:    secclass();    secclass(int newitem, int thatitem);    ~secclass();     int getsecitem();    void setsecitem(int newitem);  };  #endif   // implementation of secclass.h // secclass.cpp  #include "secclass.h"  using namespace std;  secclass::secclass() {  int *setsecinitial = new int; *setsecinitial = 16; secitem = setsecinitial; }  secclass::secclass(int newitem, int thatitem) : firstclass(thatitem) {     secitem = &newitem; }  secclass::~secclass(){}  int secclass::getsecitem() {     return *secitem; }  void secclass::setsecitem(int newitem)  {     secitem = &newitem; }   // main program #include <iostream> #include "firstclass.h" #include "secclass.h"  using namespace std;  int main() {  firstclass classa; cout << "classa item: " << classa.getitem() << endl << endl;  firstclass classz(86); cout << "classz item: " << classz.getitem() << endl << endl;  secclass classb; cout << "classb first item: " << classb.getitem() << endl; cout << "classb second item: " << classb.getsecitem() << endl << endl;  secclass classc(72, 210); cout << "classc first item: " << classc.getitem() << endl; cout << "classc second item: " << classc.getsecitem() << endl;   return 0; }

your constructor

void firstclass::setitem(int thatitem)  {     item = &thatitem; }

is doing bad thing, storing address of temporary object (the int passed constructor).

that int destroyed right after returning constructor , item pointer pointing memory area has been reused else.

anything can happen when kind of things (including daemons flying out of nostrils) don't that.


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