Cysneros, Nelson A CIV SPAWAR SSC PAC, 56510 wrote:
So sorry if this is a way too obvious question but what is the
difference between observer_ptr and ref_ptr? And when would you use
one over the other?
osg::observer_ptr : Smart pointer for observed objects, that
automatically set pointers to them to null when they deleted
osg::ref_ptr : Smart pointer for handling referenced
counted objects
They seem to do the same thing. At least I was able to replace all
observer_ptr with ref_ptr and the example still compiled and ran.
They're quite different, actually. When a ref_ptr is assigned the
address of an object, it increases the reference count on the object.
Likewise, when it is detached from the object (either by deleting the
ref_ptr, letting it go out of scope, or assigning it a different
address), the reference count on the first object is decreased.
Whenever a Referenced object's reference count drops to zero, the object
is deleted.
observer_ptr never changes the reference count of the object to which it
points. The main benefit of an observer_ptr is that when the pointed
object is deleted, the value of the observer_ptr is automatically set to
NULL.
For example:
observer_ptr<Node> nodeObs;
ref_ptr<Node> nodeRef;
nodeRef = new Node(); // Node's ref count is now one
nodeObs = nodeRef.get(); // Node's ref count is still one
nodePtr = NULL; // Node's ref count is now zero, and is deleted
// nodeObs is now NULL
OK, not a great example, but hopefully you get the idea ;-)
--"J"
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