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Problem with pointers, derived classes and vectors

General and Gameplay Programming Programming

Started by M-374 LX August 26, 2010 08:24 PM

1 comment, last by Zahlman 13 years, 8 months ago

M-374 LX

137

Author

August 26, 2010 08:24 PM

This part is okay:

ObjectExplosion expl;expl.set( 500, 300 );objectManager.addObject( &expl );

ObjectExplosion is derived from ObjectBase.
In ObjectManager, I have a vector:

std::vector<ObjectBase*> objects;

I get a segmentation fault if I call a member function from inside ObjectManager:

if ( !objects.empty() ){	objects[0]->onUpdate();}

My current project: Lyjok's World, an open source, cross-platform horizontal shoot 'em up.

SiCrane

11,840

August 26, 2010 08:28 PM

It looks like you decided to store a pointer to a local stack variable. The variable gets destroyed after its scope exits and your vector is left holding a pointer to essentially random garbage. You probably want to allocate the variable on the heap with new.

Zahlman

1,682

August 27, 2010 04:17 PM

Quote:Original post by M-374 LX
This part is okay:

*** Source Snippet Removed ***]

No, it isn't. As soon as the function ends, 'expl' does not exist any more, and the objectManager's pointer is pointing at garbage.

It looks like you are only using pointers in your vector so that you can get polymorphism. You should instead use some kind of smart pointer, or better yet, use boost::ptr_vector as your container instead of std::vector.

Problem with pointers, derived classes and vectors

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