c++ - Delete dynamically allocated derived objects - Polymorphism -

i cannot figure out how delete dynamically allocated subclasses through basepointer. allocation in app-class , how delete allocated objects withing main-method?

#include <iostream>  using namespace std;  class base {  public:    virtual void print() = 0;    virtual ~base() {       cout << "base destructor\n";    } };  class sub1 : public base {  public:    void print() {       cout << "i sub1!\n";    }    ~sub1() {        cout << "sub1 destructor\n";    } };  class sub2 : public base {  public:    void print() {       cout << "i sub2!\n";    }    ~sub2() {        cout << "sub2 destructor\n";    } };  class app {  public:     app(base *&b) {       b = new sub1;       b = new sub2;    } };   int main() {     base *b;    b = null;     app app(b);    return 0;  } 

the minimum fix leaks be:

class app {  public:     app(base *&b) {       b = new sub1;       delete b;      // chance since next statement overwrites pointer.       b = new sub2;    } };   int main() {     base *b;    b = null;     app app(b);     delete b;     return 0; } 

but doesn't seem sensible program. need figure out you're trying sub1 , sub2. can't have single pointer pointing 2 separate objects @ same time.

furthermore, better off learning use std::unique_ptr, since keeps ownership of points , deletes when appropriate.

so using std::unique_ptr minimum change code is:

class app {  public:     app(std::unique_ptr<base> & b) {       b.reset(new sub1);       b.reset(new sub2);    } };   int main() {     std::unique_ptr<base> b;     app app(b);     return 0; } 

there no manual delete statements. , there no memory leaks.

(the useless sub1 issue still there, that's design issue have figure out since don't know want program in end.)