Thread: Pointer to vector, scope and Locals

Hello fellow programmers,

I thought I had the basic stuff covered and started implementing an algorithm. Now the algorithm is finished and initial tests tells me that is works with respect to the solution it produces. Unfortunately it seems that the code does not scale with the problem instances I give it.

I have revised the method and it seems impossible that its the theory that is bugged. It _should_ scale reasonably. Hence, my money is on my poor implementation of the algorithm.

Looking at the Debug-> Windows -> Locals (Visual Studio 2008), I see a lot of variables I thought was deleted long ago. Also the size of them seems excessive. So I am thinking I have a memory leak. Well, leak might be a strong word, since I think the real problem is that I thought vectors from the STL behaved in a certain way.

The code it self is rather long (2000 lines +) so I will try to simplify my question regarding the vectors behavior.

Code:

//A function definition before the main

InitializeVector(vector<int>* pNumber)
{
vector<int> temp;
//Do stuff with the vectors
} 

VectorFun()
{
vector<int> NumberVector;
vector<int>* pNumberVector;
pNumberVector=& NumberVector;

InitializeVector(pNumberVector);
}

main()
{
//Somewhere in the main function
VectorFun();

My question is now, will the vector temp be completly deleted after InitializeVector is run? Also will the NumberVector and pointer be deleted after the VectorFun?

Basically, will they remain ghosts in my memory or are they dead and gone?

Thank you in advance for time spendt on this *I think* easy question.

EDIT: Fixed the assignment of the pointer as stated in #2

Yes 'temp' should have destructed when the stack unwinds after InitializeVector() finishes. I say *should* as i have seen broken compilers where the dtor is not called when a variable falls out of scope. It has been a looong time since this was true however (think: early 90's).

I am curious: in what way could temp (even if it did "stick around" affect your algorithm? Also the point of VectorFun() seems...odd. You create a vector of ints, then a pointer of that type, never initialize it to anything but then pass that ptr to InitializeVector()?

Ups, small mistake from my part

Code:

pNumberVector = &NumberVector

Should have been added.

I am worrying that some improper cleanup due to poor programming is making my program very slow.

EDIT: Using watch I can see that vectors like temp is still present, even though I thought it should be out of scope. Where did I go wrong?

You're passing an uninitialised pointer into InitialiseVector. There is nothing useful that you can then do with the pNumber parameter inside InitialiseVector because it's not valid. Assigning to pNumber doesn't do anything useful either.
You should really show the real code, because I'd guarantee you've got bugs in this area.