C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Iterator pipes          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Nicola Musatti Guest Posted: Wed Aug 25, 2004 8:46 pm    Post subject: Iterator pipes Hallo, groupmates. Suppose I have a function that provides a sequence of elements by taking an output iterator as argument: class Element {}; void provider(SomeOutputIter<Element>); I need to pass these elements to a function that takes an input iterator range as argument: void consumer(SomeInputIter<Element>,SomeInputIter<Element>); Is there a more clever way to do it than to use a container as buffer? Ideally it would be nice to have some sort of iterator pipe that made it possible to write to an output iterator on one end and to read from an iterator range from the other. Cheers, Nicola Musatti [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Raoul Gough Guest Posted: Fri Aug 27, 2004 3:00 am    Post subject: Re: Iterator pipes [email]Nicola.Musatti (AT) ObjectWay (DOT) it[/email] (Nicola Musatti) wrote in message news:<a327cf48.0408250036.24fe18c5 (AT) posting (DOT) google.com>... Quote: Hallo, groupmates. Suppose I have a function that provides a sequence of elements by taking an output iterator as argument: class Element {}; void provider(SomeOutputIter<Element>); I need to pass these elements to a function that takes an input iterator range as argument: void consumer(SomeInputIter<Element>,SomeInputIter<Element>); Is there a more clever way to do it than to use a container as buffer? Ideally it would be nice to have some sort of iterator pipe that made it possible to write to an output iterator on one end and to read from an iterator range from the other. I assume you mean interleaving the operations of the producer and the consumer? i.e. the producer produces one Element, and the consumer then processes this one element. Otherwise, I don't see any way to work this other than by buffering the entire producer output and then passing all this to the consumer. The problem being of course, that the consumer function isn't called once per element, but once for a whole range of elements. It would have to wait somehow internally until each new element becomes available, e.g. via cooperative multi-tasking. Modula-2 had neat support for this (as "co-routines"), IIRC. It's also possible to implement this on top of generic threading, but I don't see how you would do it in standard C++. Unix-like shells do it, of course, by starting processes in parallel and connecting them via pipes, which would require some kind of external representation of the Elements. -- Raoul Gough. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Michiel Salters Guest Posted: Fri Aug 27, 2004 3:06 am    Post subject: Re: Iterator pipes [email]Nicola.Musatti (AT) ObjectWay (DOT) it[/email] (Nicola Musatti) wrote in message news:<a327cf48.0408250036.24fe18c5 (AT) posting (DOT) google.com>... Quote: Hallo, groupmates. Suppose I have a function that provides a sequence of elements by taking an output iterator as argument: class Element {}; void provider(SomeOutputIter<Element>); I need to pass these elements to a function that takes an input iterator range as argument: void consumer(SomeInputIter<Element>,SomeInputIter<Element>); Is there a more clever way to do it than to use a container as buffer? Yes, sort-of. Write an output iterator and implement its operator* like this: SomeOutputIter::operator* returns proxy<Element>, proxy<Element>::operator=(Element e) calls consumer(&e,(&e)+1); Of course, this will call consumer more than once, but that is unavoidable anyway. provider may output many more elements than you could fit in your buffer, or take several days. provider might not even return! Regards, Michiel Salters. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Nicola Musatti Guest Posted: Fri Aug 27, 2004 1:02 pm    Post subject: Re: Iterator pipes [email]RaoulGough (AT) yahoo (DOT) co.uk[/email] (Raoul Gough) wrote in message news:<a3390f41.0408260521.51e2834b (AT) posting (DOT) google.com>... Quote: Nicola.Musatti (AT) ObjectWay (DOT) it (Nicola Musatti) wrote in message [...] Is there a more clever way to do it than to use a container as buffer? Ideally it would be nice to have some sort of iterator pipe that made it possible to write to an output iterator on one end and to read from an iterator range from the other. I assume you mean interleaving the operations of the producer and the consumer? i.e. the producer produces one Element, and the consumer then processes this one element. Otherwise, I don't see any way to work this other than by buffering the entire producer output and then passing all this to the consumer. Exactly. Quote: The problem being of course, that the consumer function isn't called once per element, but once for a whole range of elements. It would have to wait somehow internally until each new element becomes available, e.g. via cooperative multi-tasking. Modula-2 had neat support for this (as "co-routines"), IIRC. It's also possible to implement this on top of generic threading, but I don't see how you would do it in standard C++. To tell the truth I was aware of the problem. I asked just in case I missed some detail that could be exploited to construct a clever solution to my problem. Without wishing to intrude the current heated discussion on C++ and threads, I'd just like to note that my suggested iterator pipe would make a convenient high level communication/synchronization mechanism. Cheers, Nicola Musatti [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top jon hanson Guest Posted: Sat Aug 28, 2004 2:43 am    Post subject: Re: Iterator pipes [email]Nicola.Musatti (AT) ObjectWay (DOT) it[/email] (Nicola Musatti) wrote in message news:<a327cf48.0408250036.24fe18c5 (AT) posting (DOT) google.com>... Quote: Hallo, groupmates. Suppose I have a function that provides a sequence of elements by taking an output iterator as argument: class Element {}; void provider(SomeOutputIter<Element>); I need to pass these elements to a function that takes an input iterator range as argument: void consumer(SomeInputIter<Element>,SomeInputIter<Element>); Is there a more clever way to do it than to use a container as buffer? Ideally it would be nice to have some sort of iterator pipe that made it possible to write to an output iterator on one end and to read from an iterator range from the other. Cheers, Nicola Musatti If you allow multi-threading then the pipe could block the producer from writing or the consumer from reading until the other is ready, i.e. they would synchronise at the point of writing to and reading from the pipe. without threads, you'd either have to have the producer "pushing" the items, or the consumer "pulling" them. in the first case the OutputIterator would call the consumer as items were written to it, and in the second case when an item was requested from the InputIterator it would call the producer for another item. jon [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top George van den Driessche Guest Posted: Mon Sep 06, 2004 8:34 pm    Post subject: Re: Iterator pipes "Nicola Musatti" <Nicola.Musatti (AT) ObjectWay (DOT) it> wrote Quote: Hallo, groupmates. Suppose I have a function that provides a sequence of elements by taking an output iterator as argument: class Element {}; void provider(SomeOutputIter<Element>); I need to pass these elements to a function that takes an input iterator range as argument: void consumer(SomeInputIter<Element>,SomeInputIter<Element>); Is there a more clever way to do it than to use a container as buffer? Ideally it would be nice to have some sort of iterator pipe that made it possible to write to an output iterator on one end and to read from an iterator range from the other. Some assumptions I made when reading your post: - a single call to provider() writes through the supplied output iterator repeatedly (once for each element it wants to provide). - a single call to consumer() reads repeatedly until the two supplied input iterators become equal. - you're not going to put the two function calls in different threads. Since you can't have both function calls executing simultaneously, you're either going to have to buffer the result or call one or other function multiple times. You could have some sort of custom output iterator, maybe. It would forward each output element to the consumer specified in its constructor. But really that's no different from having a buffer of unit size. George [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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