Identifying memory management issues-CodePudding

#include "A.h"
int main (int argc, char*argv[]){
A * p_a1 = new A();
A * p_a2 = p_a1;
delete p_a1;
p_a1 = 0;
delete p_a2 <br>

Could this code where A is some class lead to memory management issues?
My Thoughts:
The first line will create a pointer to A. I am not sure if this will allocate memory for A, too, or will it just assign an address? The second pointer p_a2 points to the exact location.
delete p_a1 will delete the allocated memory, which probably didn't have anything p_a1=0, making it null. delete p_a2. We are then deleting the null pointer, which probably won't affect
Could this lead to any memory leakage or issues?

CodePudding user response：

Deleting the same object twice is definitely a memory management issue. delete p_a1; does delete the object pointed to by p_a1, then delete p_a2 tries to delete the very same object.

Remember: You are not deleting pointers, but you delete the object they are pointing to.

Raw new is always a code smell and a potential source of bugs. Your code should look like this instead:

#include "A.h"
int main (int argc, char*argv[]){
   A a;
}

Frankly, given your question imho one can either only scratch the surface or write a long article to explain important basics. I opted for the first and refer you to a book for more details: The Definitive C Book Guide and List

CodePudding user response：

Your problem is that p_a1 and p_a2 are independant pointers which at a time happen to point to the very same object.

After

delete p_a1;
p_a1 = 0;

all is fine from a p_a1 point of view: the object it pointed to has been deleted, and the pointer itself as received a nullptr value, so it is now safe to do delete p_a1 again.

But p_a2 has not been changed and now points to an object that has reached its end of life. So it has become a dangling pointer and dereferencing it or deleting it will invoke UB.

If you want p_a2 to be equivalent to p_a1 you should make it a reference:

A* &p_a2 = p_a1;

Now after p_a1 = 0, p_a2 is a reference to a null pointer and it can safely be deleted.