How do delete items in a vector if using remove_if and items are pointers to objects?

Question

I fear that I am running into memory leak issues by doing the following:

(Sample code)

class myItem //random container stuff mostly. All primatives.
{
    int index;
    char* name;
    int val1;
    int val2;
};

class vecList
{

    vector< myitem* > *myVec;

    void delete()
    { 
        MyVec->erase(std::remove_if(myVec->begin(), MyVec->end(), IsMarkedToDelete), MyVec->end()); //leak here?
    }
};

Erase doesn't free the memory if it's a pointer, right? If I wasn't using remove_if, I could call delete on the pointer before destroying it. How would I do it in this case? Smart Pointers? I'd prefer not to re-implement everything with them and I don't really want to add the boost library.

Thanks!

Answer 1

You could just delete the item in your IsMarkedToDelete function when it returns true.

Answer 2

If the only pointers to the object were in the vector, then you've leaked memory as soon as you call remove_if. remove_if moves the pointers which you are keeping down, but it doesn't say anything about the values behind the iterator it returns. Thus if you have something like [a, b, c, d] (where a, b, etc. represent different pointers), then after e = remove_if( v.begin(), v.end(), matches(b) ), your vector might (and probably will) look like [a, c, d, d], with e pointing to the second d, and all trace of b lost forever.

The obvious solution would be to use shared_ptr in the vector; this would ensure that any pointer which ended up removed from the vector would be deleted. Failing that, you can use two passes: the first would be a for_each with something like:

struct DeleteIfCondition
{
    void operator()( ObjectType* &ptr ) const
    {
        if ( condition( *ptr ) ) {
            ObjectType* tmp = ptr;
            ptr = NULL;
            delete tmp;
        }
    }
};

std::for_each( v.begin(), v.end(), DeleteIfCondition() );

as the functional object, followed by:

v.erase( std::remove( v.begin(), v.end(), NULL ), v.end() );

Answer 3

You can use remove_if, then for_each from the return value till the end and then erase. That would, of course, make your code a bit longer. Another possibility is to store shared_ptr pointers, if your code agrees with that.

The above is a blunt lie, as Benjamin pointed out, so you're only left with "another possibility".