Thread: I don't understand...

a simple example destructor,i really donot understand the output

Code:

#include<iostream>
using namespace std;

class T {
public:
	T( double d ) : pd( new double( d ) ) { };
	~T();
private:
	double *pd;
};
T::~T()
{
	cout << ( *pd ) << endl;
//	( *pd ) = -1;
//	delete pd;
}

extern void func( T t )
{
	/* ... */
	cout << " Here " << endl;
}

void main()
{
	T t( 1.2 );
	T t1( 1.8 );
	func( t );
	func( t1 );
}

the output is like this:
Here
1.2
Here
1.8
1.8
1.2

but in my opinion,it should be
Here
1.8
Here
1.2

so why? Could anyone explain it to me?
any help is appreciated...

got it！
thx very much

Originally Posted by CornedBee

That code ought to crash, by the way, and it would if you hadn't commented out the two lines in the destructor. As it is, it has a memory leak.

It's a good example why classes with dynamic memory always need a copy constructor.

You're correct, but I doubt the reasons would be obvious to beginners. You may wish to expand on your comments......

an advice. Whenever you delete a pointer set it to null. You can use some templated function to do that automaticly for you always.

Code:

template<class Xptr> inline delete_ptr(Xptr*& p){
    delete p;
    p = NULL;
}
template<class Xptr> inline delete_array(Xptr*& p){
    delete[] p;
    p = NULL;
}

So I've seen now.
Lorin, you have to define a copy constructor, and by the way the operator=(...)