deleting a vector of pointers vs. object in c++

Question

I have a vector of pointers to an object (I have them as pointers because I will be swamping the positions around a lot, and I would imagine it would be a lot faster to just swap the pointer, rather than swapping around the whole object.

Anyway, I will ultimately need to delete the vector, but the objects that it points to still need to be valid. The documentation seems to say that it will call the destructor on every object in the vector. This makes sense when it's an array of objects, but if the array is an array of pointers to objects, will the objects that the pointers point to also be deleted, or do I need to delete them manually?

If they are deleted automatically, is the only way to keep the objects around (say they were used in a different vector) is to actually copy the objects to another location, and have the pointers in the vector point to those objects (rather than the originals)?

Thank you.

Here is a [related answer](http://stackoverflow.com/questions/4260464/does-stdlistremove-method-call-destructor-of-each-removed-element/4261074#4261074) of mine. — fredoverflow, Jan 17 '11 at 18:53

score 4 · Accepted Answer · answered Jan 17 '11 at 18:35

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Calling a destructor on a pointer value does nothing. (On the other hand, calling delete on a pointer value runs the destructor for the pointed-to object, and frees the memory.)

In the case of an array of pointers to objects, you must free the objects manually if that's what you want.

answered Jan 17 '11 at 18:35

Greg Hewgill

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Thank you. I'm marking this as the answer as it provides the best explanation. (so far anyway) – Leif Andersen Jan 17 '11 at 18:45

score 1 · Answer 2 · answered Jan 17 '11 at 18:37

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If you have a vector of pointers, the actual objects should still be around if you delete (or clear) the vector.

answered Jan 17 '11 at 18:37

helloworld922

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score 1 · Answer 3 · answered Jan 17 '11 at 18:37

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You could use smart pointers in your vector, such as Boost shared_ptr.

answered Jan 17 '11 at 18:37

Fred Larson

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Actually, it sounds like normal vanilla pointers are exactly what he wants here. – T.E.D. Jan 17 '11 at 18:40
@T.E.D.: Yeah, I think I read the question backwards. 8v) Still, using `shared_ptr` might not be a bad idea if it's used for everything that uses the objects. – Fred Larson Jan 17 '11 at 18:41
Mmm...these look interesting. Thank you for bringing it to my attention. – Leif Andersen Jan 17 '11 at 18:47

score 1 · Answer 4 · answered Jan 17 '11 at 18:37

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It will indeed destruct any objects in the container. However, since all the objects in your container are pointers, that won't do much of anything.

Reading your question, that sounds like exactly what you want it to do, so you are good.

answered Jan 17 '11 at 18:37

T.E.D.

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score 1 · Answer 5 · answered Jan 17 '11 at 18:38

It does not matter - that's the reason for the delete keyword. If you go out of scope, then the object's destructor is called. If a pointer goes out of scope, then it tends to be a memory leak. The same applies here, so you will not have to do anything special.

They will continue to exist.

score 0 · Answer 6 · answered Jan 17 '11 at 19:05

Anyway, I will ultimately need to delete the vector, but the objects that it points to still need to be valid. The documentation seems to say that it will call the destructor on every object in the vector. This makes sense when it's an array of objects, but if the array is an array of pointers to objects, will the objects that the pointers point to also be deleted, or do I need to delete them manually?

First, read this: http://crazyeddiecpp.blogspot.com/2010/12/pet-peeve.html

Now ask yourself, does the documentation say that vector deletes every object that every object it contains points at?

If you can answer that question with 'No' then there you have it.

If you can answer that question with 'Yes'...well...try different documentation.

deleting a vector of pointers vs. object in c++

6 Answers6