Home » U++ Library support » U++ Core » Wrong(?) ASSERT in Vector<>::Insert()
| Wrong(?) ASSERT in Vector<>::Insert() [message #27807] |
Wed, 04 August 2010 23:33  |
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Hello,
I just hit a problem in Vector code and I feel a need for explanation  . Have a look at this code #include <Core/Core.h>
using namespace Upp;
CONSOLE_APP_MAIN{
Vector<int> v;
v.Add(123);
v.Insert(0,v[0]);
}
I would expect it to insert a deep copy of the first element of the Vector and place it before the original. The actual result is that the code hits an assert in the Insert function: template <class T>
void Vector<T>::Insert(int q, const T& x, int count) {
if(!count) return;
ASSERT(&x < vector || &x > vector + items);
RawInsert(q, count);
DeepCopyConstructFill(vector + q, vector + q + count, x);
}
As you can see, it check if the inserted data are part of the object itself. And of course, in the example above, they are.
Now, can someone explain me the reason for this assert? I fail to see how it could be harmful to make a deep copy of one of the elements inside...
If there is no real reason for this, I would like to see that assertion removed. There are also the same or similar assertions in the other variations of Insert which can be probably removed.
In my actual code I had to work around this by first making a deep copy of the copied element in temporary object and than inserting that. But I use quite big objects, not just int, so this workaround introduces is not only ugly, but also slow.
Best regards,
Honza
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| Re: Wrong(?) ASSERT in Vector<>::Insert() [message #27857 is a reply to message #27807] |
Fri, 06 August 2010 20:51  |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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maybe because the adding of another element could lead to destroying (remember Moveable<>) the underlying vector space, (of which your first element is part of and render your reference to the first element invalid) and you would use an invalid source element reference for making the deep copy.
array flavor shouldnt have this problem i think.
correct me if i'm wrong..
[Updated on: Fri, 06 August 2010 20:55] Report message to a moderator |
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| Re: Wrong(?) ASSERT in Vector<>::Insert() [message #27997 is a reply to message #27807] |
Fri, 13 August 2010 09:34 |
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mirek
Messages: 13975
Registered: November 2005
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Ultimate Member |
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| dolik.rce wrote on Wed, 04 August 2010 17:33 |
Hello,
I just hit a problem in Vector code and I feel a need for explanation . Have a look at this code #include <Core/Core.h>
using namespace Upp;
CONSOLE_APP_MAIN{
Vector<int> v;
v.Add(123);
v.Insert(0,v[0]);
}
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It is classical and nasty bug.
Insert expects a reference, but at the same time invalidates references to v.
Not that in this particular case, we could workaround it in Vector code, but there are other similar cases where this is not quite possible:
http://www.ultimatepp.org/srcdoc$Core$Caveats$en-us.html
so I decided to forbid them all.
(And thanks kohait, you are 100% right).
And yes, I am not happy about this, but I guess ASSERT is best we can get here....
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