Question

I have query regarding std::map.

if I have a std::map like:

std::map <T1, T2*> my_map;
T1 t;
T2* tt = new T2;
my_map[t]=tt;

who is responsible to clean this container, Will destructor of T2 will take care of it (T2* tt). Also if I want to retain this container throughout the program, where should I clean it.

Thanks

Answer 1

The map destroys the objects stored in the map. The map stores some T1 objects, which will be destroyed, and it stores some T2 pointers, which will be destroyed.

But it does not store actual T2 objects. So no T2 objects will be destroyed.

Raw pointers do not have ownership of the objects they point to. So when a pointer is destroyed, it will not delete whatever it points to.

Generally speaking, when you have a pointer, there is no way to know if

• it points to a valid object at all (you don’t want to call delete on some random garbage in memory),
• the object it points to has been allocated with new (if it has been allocated in another way, it should not be deleted with delete), or
• if there are other pointers that also point to the same object (in which case only one of them should call delete. Which one?)

So even if you wanted to, there is no way to automatically delete an object when a pointer to it is destroyed.