"benben" <benhongh@hotmail.com> wrote in message
news:42c89194$0$20855$afc38c87@news.optusnet.com.a u...[color=blue]
>
> "Jim Langston" <tazmaster@rocketmail.com> wrote in message
> news:DZXxe.1010$x82.851@fe03.lga...[color=green]
>>
>> "benben" <benhongh@hotmail.com> wrote in message
>> news:42c7839b$0$20029$afc38c87@news.optusnet.com.a u...[color=darkred]
>> >> Please see my reply to Donovan.
>> >
>> > Hmm, I don't see any of your reply to Donovan...or is it in another
>> > discussion?[/color]
>>
>> Here is the reply I was talking about
:
>>
>>
>> "Donovan Rebbechi" <abuse@aol.com> wrote in message
>> news:slrndcbvq2.3r8.abuse@panix2.panix.com...[color=darkred]
>> > [SNIP]
>> > Use templates.
>> > template <typename iter>
>> > void printit ( iter start, iter end )
>> > {
>> > for (; start!=end; ++start)
>> > std::cout << *start << std::endl;
>> > }
>> >
>> > or you could simplify by using the standard library, and generalise to
>> > allow other ostreams:
>> >
>> > template <typename iter>
>> > void printit (iter start, iter end,std::ostream & out = std::cout)
>> > {
>> > std::copy(start,end,std::ostream_iterator(out, "\n"));
>> > }
>> >
>> >
>> > printit (MyVector.begin(),MyVector.end());
>> > printit (MyVector.rbegin(),MyVector.rend());[/color]
>>
>> I can see how either of these methods would work in the example I had[/color]
> given,[color=green]
>> simply outputting the entire vector, but the iterator needs to suvive
>> between calls.
>>
>> class CChatBuffer
>> {
>> private:
>> std::vector<std::string>::reverse_iterator r_MIter; // Message
>> Iterator
>> std::vector<std::string> MessageBuffer; // Buffer to hold messages
>> from
>> server
>> public:
>> void ResetRead( bool Reverse );
>> std::string GetLine();
>> // Other class variables/methods not shown
>> };
>>
>> void CChatBuffer::ResetRead( bool Reverse )
>> {
>> if ( ! Reverse )
>> r_MIter = MessageBuffer.rend(); // Not allowing forward yet, so set[/color]
> to[color=green]
>> end
>> r_MIter = MessageBuffer.rbegin();
>> }
>>
>> std::string CChatBuffer::GetLine()
>> {
>> if ( r_MIter != MessageBuffer.rend() )
>> return (*r_MIter++);
>> else
>> return "";
>> }
>>
>> I can see also storing iter_start and iter_end in my class (didn't think[/color]
> of[color=green]
>> that) and setting them to .rbegin() or .rend() in my ResetRead. I can't
>> see, however, how I could save the iterator in my class between calls of
>> GetLine so that GetLine knows if it's a forward or reverse iterator. I
>> played around with some test code just now but still couldn't figure out[/color]
> how[color=green]
>> to do it.
>>
>>
>>[/color]
>
> Ok, I think I start to understand your problem now.
>
> Basically, you are trying to dynamically reverse the access direction of
> an
> iterator. What is in my mind, is about three different ways of achieving
> it.
> But switching forward and reverse iterator is not a good idea because it
> is
> typically resolved at compile time, not at runtime.
>
> First, std::vector<T>::iterator defines a bidirectional iterator, so you
> can
> use ++ for pointing to the next element, or -- for pointing to the
> previous
> element.[/color]
Yes, I know this, but then I would need an if statement to determine weather
to increment or decrement it. I suppose the trinary function would work
though.
return ((reverse)?*r_MIter++:*r_MIter--));
Hmm.. this might work using the storing of the iterator begin and end in
variables. I'll have to test this.
[color=blue]
>
> Second, std::vector supports subscription. So using an integer to store
> the
> index can make your class much easier to read and write.[/color]
Doesnt' solve problem of wanting to use as few conditional statements as
possible.
[color=blue]
> And finally, if applicable, you can merge ResetRead and GetLine, so
> GetLine
> now takes an additional parameter bool reverse.[/color]
I could do this. But dont see how it will help. GetLine is called line by
line, not for the whole vector. It's being used (currently) to display text
to the screen using directx calls, later to write buffer to text file, or
any other thing my program needs to deal with text buffers.
[color=blue]
> And worth to note, the iterator returned by calling begin() points to the
> first element, end() the ONE PAST the last element; rbegin() the last
> element, and rend() the ONE BEFORE the first element.[/color]
Noted and understood, which is only reason same logic works for both forward
and reverse iterators as long os you use proper .begin() or .rbegin() etc...
thanks, got some testing to do.
