ATL / WTL / STL

Re: List of object or list of pointers to objects?

18-Aug-03 23:30

Never ever put an auto_ptr in a standard container.
auto_ptr has a funny copy semantic, and you end up with your objects getting deleted while being copied.
You could use boosts[^]shared_ptr, which does reference counting and has a more intuitive copy semantic.
Or you can simply make your own class: Constructor that takes an Book-object, a few Get/Set functions for the underlying object, assignment-op and copy constructor that deletes its contained object and takes ownership of the new one and a set of operators that access the contained Book-object to determine the sorting sequence.

Who is 'General Failure'? And why is he reading my harddisk?!?

Andrew Walker19-Aug-03 1:27

Andrew Walker

19-Aug-03 1:27

All of the sort algorithm's in STL have approximately O(N log N) complexity.

Maps on the other hand have an insertion complexity of O(N * log(size() + N)), so it may be quicker to add all of the books to a map, which is always sorted rather than having to do it explicitly. It may depend on the application.

SGI STL Complexity[^]

jhwurmbach correctly pointed out that using pointers will be cheaper, but missed that the sort algorithms can optionally take a predicate. In cases like this, you are almost always going to use a functor to sort your data based on your criteria.

jhwurmbach wrote
Maybe you can write some sort of proxy-class. ... Additionally you would probably need ...

This isn't really true, raw pointers are fine, you don't need anything extra in the container, the extra stuff will go into the sort criteria function object.

If you can keep you head when all about you
Are losing theirs and blaming it on you;
If you can dream - and not make dreams your master;
If you can think - and not make thoughts you aim;
Yours is the Earth and everything that's in it.

Rudyard Kipling

STL list

Anthony_Yio18-Aug-03 21:01

18-Aug-03 21:01

Hello,

I would like to insert an element into a list container during iteration.
How would I do that? Please refer my comment in the code.

<br />
list<long> myList;<br />
myList.push_back(2);<br />
myList.push_back(4);<br />
myList.push_back(6);<br />
myList.push_back(8);<br />
myList.push_back(10);<br />
myList.push_back(12);<br />
myList.push_back(14);<br />
<br />
list<long>::iterator lItemItr;<br />
for(lItemItr= myList.begin(); lItemItr!= myList.end(); lItemItr++)<br />
{<br />
   if(*lItemItr == 8)<br />
   myList.insert( lItemItr + 1, *lItemItr); //this give compiler error<br />
//I would like to insert a 8 into the  after the 10.<br />
//So that my list contain {2, 4, 6, 8, 10, 8, 12, 14}<br />
}

How would I do that?

thank you

Sonork 100.41263:Anthony_Yio

jhwurmbach18-Aug-03 21:38

18-Aug-03 21:38

If you want to insert after the 10, you need to compare with 10, not withsome other number!?!
Also, MSDN states about std::list::insert: "Each of the member functions inserts, before the element pointed to by it in the controlled sequence, a sequence specified by the remaining operands. The first member function inserts a single element with value x and returns an iterator that points to the newly inserted element."
SO, this lines should work:

if (*lItemIter == 10)
{
  lItemIter++;                    //step to the element after the 10
  list<long>::iterator newElem = myList.insert (lItemIter, 8);   //insert 8 before it (e.g. after the 10)
}

Who is 'General Failure'? And why is he reading my harddisk?!?

Anthony_Yio18-Aug-03 22:20

18-Aug-03 22:20

Probably I would play around with the return "newElem" to do some trick here.

thanks

Sonork 100.41263:Anthony_Yio

Jeremy Pullicino18-Aug-03 21:39

Jeremy Pullicino

18-Aug-03 21:39

<br />
list<<long>>::iterator lItemItr;<br />
for(lItemItr= myList.begin(); lItemItr!= myList.end(); lItemItr++)<br />
{<br />
          if(*lItemItr == 10) myList.insert( lItemItr , 8);<br />
}

Jeremy Pullicino
C++ Developer

Homepage

Anthony_Yio18-Aug-03 22:03

18-Aug-03 22:03

Of course, I could just do it this way but this codes is just to demonstrate my another problem. It is not my actual problem. My actual problem is way too long to be explained here.
In short. I do not want to insert in this direct way.
if(*lItemItr == 10) myList.insert( lItemItr , 8);

I want to insert during if(*lItemItr == 8)

Any idea?

thank you

Sonork 100.41263:Anthony_Yio

jhwurmbach18-Aug-03 22:09

18-Aug-03 22:09

Anthony_Yio wrote:
I want to insert during if(*lItemItr == 8)
Any idea?

No.
Insert during a comparsion? How could that work?
Do you mean you want to assign to some iterator?

I am sorry, but as long as your actual problem is way too long to be explained, you will get only solutions that are way too short to be helpful.

Who is 'General Failure'? And why is he reading my harddisk?!?

Anthony_Yio18-Aug-03 22:23

18-Aug-03 22:23

Not during comparison.

Anyway,
it is okay. I will work it out.

Thanks.

Sonork 100.41263:Anthony_Yio

Anthony_Yio18-Aug-03 22:37

18-Aug-03 22:37

I think I should stick to vector.

vector allows iterator + 1;

Sonork 100.41263:Anthony_Yio

jhwurmbach18-Aug-03 23:22

18-Aug-03 23:22

Anthony_Yio wrote:
I think I should stick to vector.

Depends on what you want:
Insertion into the middle of a vector is extremely expensive, as the vector is guarateed to occupy continous memory, and needs to copy anything after the insertion point.
Good is that you can do iterator arithmetics like it+6

List handles insertion in the middle better, but you cant do iterator arithmetics.
You can only increment iterators, i.e. move to the next element.

Who is 'General Failure'? And why is he reading my harddisk?!?

Anthony_Yio19-Aug-03 17:03