A very common mistake

#ifndef __BADPARENT_H__

#define __BADPARENT_H__

class badparent

{

public:

badparent(){};

};

#endif /* __BADPARENT_H__ */

#ifndef __CHILD_H__

#define __CHILD_H__

#include "badparent.h"

class child : public badparent {

public:

child();

~child();

protected:

int *pointer;

};

#endif /* __CHILD_H__ */

#include "child.h"

#include <iostream.h>

int main()

{

child *c;

int i = 0;

while ( i++ < 5)

{

c = new child();

delete c;

}

}

#include "child.h"

#include <iostream.h>

child::child()

{

pointer = new int [1024];

cout << " in child's constructor" << endl;

}

child::~child()

{

delete [] pointer;

cout << " in child's destructor" << endl;

};

“child” is doing all by the books: all memory allocated is freed again in the destructor. We print messages so that we can see the constructor and destructor being called.

in child's constructor

in child's destructor

in child's constructor

in child's destructor

in child's constructor

in child's destructor

in child's constructor

in child's destructor

in child's constructor

in child's destructor

looks ok (and is ok) -- for each constructor called, we call the destructor, all fine.

So why is the parent “bad”?

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