Thread: Is this right

> X = new Test;
This is the only thing you allocated, so the only thing you can delete is X
  delete X;

> int *ptr;
Whilst this is a pointer, which you initialise with
> ptr = &a;
You didn't initialise it by calling new, so its wrong to call
  delete ptr;

ok quick look at dynamic memory....

You ask the operating system for a chunk of memory on the heap by using the new keyword. This returns a pointer to the given memory or either throws std::bad_alloc or returns 0 if unsuccessful (depends on compiler mostly).Dont lose this pointer because it is the key to freeing up the memory when you have finished with it.

Code:

#include<iostream>
using namespace std;

class A
{
private: int x;
public : A() : x(100) {}
            print() {cout<<x;}
};

int main()
{
// lets dynamically create an instance of A
A* pointer_to_A = new A;
if(pointer_to_A)
{
pointer_to_A ->print();
//ok finished with memory so now we free it like this
delete pointer_to_A;
//but hang on pointer_to_A still points to our freed memory so for safety
pointer_to_A=NULL;
}
// ok now a dynamic array of A objects
A* pointer_to_array = new A [5];
if (pointer_to_array)
{
for(int i=0;i<5;i++)
{
pointer_to_array[i] -> print();
cout<<endl;
}
// now we are finished with it we free it like this
delete [] pointer_to_array;
pointer_to_array=NULL;
}
return 0;
}

anything there you dont follow?

there are 3 ways to get memory dynamically and these all need their own freeing mechanism....

1) malloc() ...... you have to use free()
2) new ...... you have to use delete
3) new[] ...... you have to use delete[]

Any pointer that doesn't point to dynamically allocated memory does not have to be freed, but it is still good practice to set it to null when you are through using it. (unless the pointer goes out of scope right away).