VC STL - using 'while' for traversing with iterator.

Author

using 'while' for traversing with iterator.

Corey Wirun

2005-03-02, 9:00 pm

Hi All,

I'm porting a whole 'swack' of legacy code that uses the Borland BIDS
containers to STL under Visual Studio. In this environment, I have hundreds
of code constructs that look like this:

TIterator * pIter = obj->InitIterator();

while ( *pIter )
{
Object * pListObj = ( *pIter)++;
...
}

If I carry this forward to an std::list and using list<T>::iterator, is
there a way I can 'while' my way through the objects in a std::list using
the list<T>::iterator? All the examples I've seen in text books, etc., show
something like this for traversing the list:

for (iter = collection.begin(); iter != collection.end(); ++iter )
{
cout << *iter << ' ';
}

I don't have any problem converting all the constructs to use the 'for', but
it can save me w

s of time to be able to somehow 'while' my way through.

Thanks in Advance!
Corey.

Igor Tandetnik

2005-03-02, 9:00 pm

"Corey Wirun" <corey.wirun@nospam.ca> wrote in message
news:uX4Z5H2HFHA.3776@TK2MSFTNGP10.phx.gbl
> I'm porting a whole 'swack' of legacy code that uses the Borland BIDS
> containers to STL under Visual Studio. In this environment, I have
> hundreds of code constructs that look like this:
>
> TIterator * pIter = obj->InitIterator();
>
> while ( *pIter )
> {
> Object * pListObj = ( *pIter)++;

Are the parentheses really placed this way? This code never increments
the iterator, so I'm not sure how it ever breaks out of the loop.

> If I carry this forward to an std::list and using list<T>::iterator,
> is there a way I can 'while' my way through the objects in a
> std::list using the list<T>::iterator? All the examples I've seen in
> text books, etc., show something like this for traversing the list:
>
> for (iter = collection.begin(); iter != collection.end(); ++iter )
> {
> cout << *iter << ' ';
> }

Well, you can always change this to

iter = collection.begin();
while (iter != collection.end())
{
cout << *iter++ << ' ';
}

--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

Doug Harrison [MVP]

2005-03-02, 9:00 pm

Corey Wirun wrote:

>Hi All,
>
>I'm porting a whole 'swack' of legacy code that uses the Borland BIDS
>containers to STL under Visual Studio. In this environment, I have hundreds
>of code constructs that look like this:
>
>TIterator * pIter = obj->InitIterator();
>
>while ( *pIter )
>{
> Object * pListObj = ( *pIter)++;
> ...
>}
>
>If I carry this forward to an std::list and using list<T>::iterator, is
>there a way I can 'while' my way through the objects in a std::list using
>the list<T>::iterator? All the examples I've seen in text books, etc., show
>something like this for traversing the list:
>
>for (iter = collection.begin(); iter != collection.end(); ++iter )
>{
> cout << *iter << ' ';
>}
>
>I don't have any problem converting all the constructs to use the 'for', but
>it can save me w

s of time to be able to somehow 'while' my way through.

You have to arrange for a comparison with the right container.end(). It
might be possible to write a TIterator replacement that requires at most a
new constructor that takes a reference to a container or iterator range.
That way, you could avoid changing your loop patterns.

--
Doug Harrison
Microsoft MVP - Visual C++

Corey Wirun

2005-03-02, 9:00 pm

> > TIterator * pIter = obj->InitIterator();
>
> Are the parentheses really placed this way? This code never increments
> the iterator, so I'm not sure how it ever breaks out of the loop.
>

Yeah, Igor, that's what I thought when I saw it as well. Apparently the
Borland BIDS containers do some funky stuff with iterators. That's why
(*pIter) == NULL works to detect the end of the list, I guess.

Thanks for your suggestion.
C.

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