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# Creating & deleting pointers

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That's awesome guy's I really appreciate the time you've taken to explain that.

Particularly like your input larspensjo, it's a great explanation.

Right I'm off to make more spelling mistakes and get tied up in knots lol.

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One last thing.

Because of the way you have written you destructor all the memory will be released when it is called, so you have done everything right. Especially the redundant nulling of the pointers, its good practice, but might have performance issues in games.

Oh in what sense is that a bad thing, as this is definitely games coding!

However, I can't see why you are using dynamic memory for this data, why not just let the class members be a string and an int? I apreciate you may have simplified it for the question, in which case ignore this comment.

So if i want to store floating point numbers and strings they can just be basic type def calls and that will save on CPU power will it?, what would I need to use the dynamic memory for? just the initial instantiation of the class (or Animal) into a vector (as in larspensjo's example), and then delete it if the object dies in game for instance.

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what would I need to use the dynamic memory for?

To control the lifetime of objects.

When an object is created on the stack, its lifetime is bound to the scope it resides in. Similarly, the lifetime of the members inside an object is bound to the lifetime of the object. Because the lifetime of objects on the stack are predictable (LIFO ordering), allocating objects on the stack is fast. However, objects aren't always allocated and deallocated in order. The heap serves to manage dynamically allocated objects that can be allocated an deallocated in any order. By using dynamically allocated memory, you can control when and where to end an object's life.

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Thanks fastcall, upon testing the above I've hit on another 'wall'!

Using a vector creates a dynamic list of objects, and I want to kill off these objects by reducing their lifeforce muhahahaha *ahem*.
When I iterate through this list and remove the dead ones by calling the destructor to kill them off, the vector fails as the original scope of the for loop fails. How do I say check them all then delete the ones that are dead for a new list?

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The destructor is called automatically; do not manually call the destructor*.

Removing elements from a vector while iterating looks something like this:
 vector<Object*> objects; for ( vector<Object*>::iterator itr = objects.begin(); itr != objects.end(); /* empty */ ) { if ( itr->shouldBeRemoved() ) { delete *itr; // Release memory allocated for the object pointed by the pointer in the iterator itr = object.erase( itr ); } else itr ++; } 

* Unless the object was constructed using placement-new. Edited by fastcall22

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Ah that Might be why it's dying lol!. and I was using a standard for loop on the size of the vector which may explain the other error. Thanks.

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Notice the difference between "[font=courier new,courier,monospace]vector<Object*> objects;[/font]" and "[font=courier new,courier,monospace]vector<Object> objects;[/font]" (the '*').

The first is a vector of pointers to objects (where you have to do new/delete on individual objects), and the second is a vector of objects (no new/delete needed, it is all automatic). As mentioned above by fastcall22, what you use depends what requirements you have on the lifetime of the individual objects.

Notice also that std::vector is efficient when adding elements, but less efficient when removing elements that are not in the end. It is done by moving all subsequent elements "down", to overwrite the space of the removed element.

If you want to have long lists where you add and remove elements randomly, using std::list may be better. In practice, it is implemented as a linked list. While insertion and removals are quick, it is not possible to do indexing. There are a couple of other nice containers, each optimized for a special purpose.

As the API to the container types are similar, but not identical, it means it is usually easy to start the implementation using one container type, and change it later when you find you have special performance requirements. For example, iterating over a vector as fastcall22 shows is the same syntax that is used to iterate over a std::list. And then, in C++11, there is special syntactical support for iteration statements.

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vector objects;
for ( vector::iterator itr = objects.begin(); itr != objects.end(); /* empty */ ) {
if ( itr->shouldBeRemoved() ) {
delete *itr; // Release memory allocated for the object pointed by the pointer in the iterator
itr = object.erase( itr );
} else
itr ++;
}

This is evaluating them all to death when only 1 of them is at zero (m_Health <= 0), I don't get why?

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If you want to have long lists where you add and remove elements randomly, using std::list may be better. In practice, it is implemented as a linked list. While insertion and removals are quick, it is not possible to do indexing. There are a couple of other nice containers, each optimized for a special purpose.

This is the bit i'm trying to figure out, I wan't lots of baddies being generated and killed so i'm looking for the most efficient way to do it. If it's lists then I'll go off and research them over vectors.

What I essentially want are lots of objects all with specific data that can be called on depending on the users distance from that object. Like an interaction thing, so the calls for checking stats etc will be less the further away the user is from them.

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This is the bit i'm trying to figure out, I wan't lots of baddies being generated and killed so i'm looking for the most efficient way to do it. If it's lists then I'll go off and research them over vectors.

I'm going to put words in your mouth and say that you don't want to do that, you just want to get it working. Figuring out the most efficient way to do it is going to require you to write both methods and profile them. You only want to do that if there's an actual need for it(i.e. your game is running to slow). Stick with vectors for now.

This is evaluating them all to death when only 1 of them is at zero (m_Health <= 0), I don't get why?

Could you paste the relevant code?

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