C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Tracking information in input stream Goto page 1, 2  Next          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Adam H. Peterson Guest Posted: Fri Dec 17, 2004 12:42 am    Post subject: Tracking information in input stream I would like to make a stream or streambuf that tracks the number of lines that have been read and stuff like that (so, for example, when I get an error message, I can ask the stream for the line number and put it in error messages. I tried to create a streambuf class that held an instance of another streambuf (through parameterized inheritance) and would ferry calls from the one to the other, tracking data as it was read, but I wasn't able to get a hook that found where the data gets passed to the calling application. Has this problem already been solved? Is there a place I can look for a ready-made solution? Anyway, thanks for reading. Adam H. Peterson Back to top Mike Wahler Guest Posted: Fri Dec 17, 2004 1:02 am    Post subject: Re: Tracking information in input stream "Adam H. Peterson" <ahp6 (AT) email (DOT) byu.edu> wrote Quote: I would like to make a stream or streambuf that tracks the number of lines that have been read You don't need to create your own stream or stream buffer type to do this. Just count the newsline characters when you read. Quote: and stuff like that "stuff like that" is such a vague phrase, I won't even try to address it. Quote: (so, for example, when I get an error message, I can ask the stream for the line number and put it in error messages. Output the value of a counter which you increment when encountering a newline character. Quote: I tried to create a streambuf class that held an instance of another streambuf (through parameterized inheritance) and would ferry calls from the one to the other, tracking data as it was read, but I wasn't able to get a hook that found where the data gets passed to the calling application. I think you're making things far more complex than necessary. Quote: Has this problem already been solved? Is there a place I can look for a ready-made solution? Just do your i/o in a loop (typical way to do it anyway). Exactly how you count newlines depends upon the functions you use for your i/o. E.g. if you use cin.get(), check its return value for 'n'. If you use e.g. 'std::getline', when it returns, you know you've either encountered a newline, or EOF (or an error occurred). You can sort out what happened with e.g. 'eof()' and 'fail()' -Mike Back to top Adam H. Peterson Guest Posted: Fri Dec 17, 2004 1:11 am    Post subject: Re: Tracking information in input stream Mike Wahler wrote: Quote: "Adam H. Peterson" <ahp6 (AT) email (DOT) byu.edu> wrote in message news:cpta11$du6v$1 (AT) acs2 (DOT) byu.edu... I would like to make a stream or streambuf that tracks the number of lines that have been read You don't need to create your own stream or stream buffer type to do this. Just count the newsline characters when you read. This isn't really useful to me, though. If I have code like: void f(istream &i) { Object o; i >> o; } I don't really want to poke around inside Object's stream extraction operator, and I may be unable to. It's pretty common to have opaque I/O routines that read and write objects or data structures of various types. Often I can't instrument them, and even if I can, it usually results in pretty messy looking code when compared with the original. So I don't always have the option of keeping track of stuff as I read it --- that is, unless I can get the stream to do it for me. Quote: I tried to create a streambuf class that held an instance of another streambuf (through parameterized inheritance) and would ferry calls from the one to the other, tracking data as it was read, but I wasn't able to get a hook that found where the data gets passed to the calling application. I think you're making things far more complex than necessary. Possible. If I am, I would be grateful to know a simpler solution. (I mean simple to code, rather than simple to explain.) Quote: Has this problem already been solved? Is there a place I can look for a ready-made solution? Just do your i/o in a loop (typical way to do it anyway). Exactly how you count newlines depends upon the functions you use for your i/o. E.g. if you use cin.get(), check its return value for 'n'. If you use e.g. 'std::getline', when it returns, you know you've either encountered a newline, or EOF (or an error occurred). You can sort out what happened with e.g. 'eof()' and 'fail()' Well, that's fine if I'm reading primitive values like characters or lines. But even reading integers using >> will get me into trouble because it will consume whitespace without an opportunity for me to inspect it. And I'm thinking in general of the read-opaque-object situation. Instrumenting all the I/O routines I use reduces their encapsulation and makes them harder to read, and I believe it would be error prone. If the stream object can be made to track that information for me internally, it would (I believe) just work. Back to top Jonathan Turkanis Guest Posted: Fri Dec 17, 2004 1:43 am    Post subject: Re: Tracking information in input stream Adam H. Peterson wrote: Quote: I would like to make a stream or streambuf that tracks the number of lines that have been read and stuff like that (so, for example, when I get an error message, I can ask the stream for the line number and put it in error messages. Has this problem already been solved? Is there a place I can look for a ready-made solution? The Boost Iostreams library, which will be included with the next release of Boost (1.33), makes it easy to attach chains of filters to existing streams and stream buffers. These filters can modify data, or simply observe it, as in your case. I'm planning to add a filter which counts newlines, but haven't done so yet. Here's a simple filter for counting lines of input (untested): #include <boost/iostreams/concepts.hpp> // input_filter #include <boost/iostreams/operations.hpp> // get using namespace std; using namespace boost::io; class line_counter : public input_filter { public: line_counter() : lines_(0) { } int lines() const { return lines; } template<typename Source> int get(Source& src) { // Pass characters through unchanged. int c = boost::io::get(src); if (c == 'n') ++lines_; return c; } private: int lines_; }; (This is just an illustration; the official version will be more efficient.) It could be used as follows: #include <iostream> #include <boost/ref.hpp> #include <boost/iostreams/filtering_istream.hpp> using namespace std; using namespace boost::io; int main() { line_counter counter; filtering_istream in; in.push(boost::ref(counter)); // Push a reference to the counter in.push(cin); // Read from 'in' instead of 'cin'. counter will count the lines. ... std::cout << "lines read from std::cin = " << counter.lines() << "n"; } It's also not fairly easy to write a class extending filtering_istream which keeps track of the line count automatically. The most recent version of the library is here: http://home.comcast.net/~jturkanis/iostreams/ I plan to update it soon. Quote: Adam H. Peterson Best Regards, Jonathan Back to top Adam H. Peterson Guest Posted: Fri Dec 17, 2004 1:47 am    Post subject: Re: Tracking information in input stream Great. I love Boost and use it all the time, so I'll surely look into it. Are there any facilities in Boost 1.32 that I might be able to use to this effect? And/or do you have a good guess as to when the next Boost will be out? Thanks for the response, Adam H. Peterson Back to top Jonathan Turkanis Guest Posted: Fri Dec 17, 2004 2:02 am    Post subject: Re: Tracking information in input stream Jonathan Turkanis wrote: Quote: It's also not fairly easy to write a class extending I'm pretty sure I meant to say "It's also failry easy" ... Jonathan Back to top Jonathan Turkanis Guest Posted: Fri Dec 17, 2004 2:25 am    Post subject: Re: Tracking information in input stream Adam H. Peterson wrote: Quote: Great. I love Boost and use it all the time, so I'll surely look into it. Are there any facilities in Boost 1.32 that I might be able to use to this effect? I'm afraid not. Quote: And/or do you have a good guess as to when the next Boost will be out? As far as I know 1.33 hasn't been scheduled. Since 1.32 was just released, it's sure to be a few months off. Nearly 10 months elapsed between release 1.31 and 1.32, but this was unusual. I'm hoping the next release will be in three or four months. Quote: Thanks for the response, Adam H. Peterson Jonathan Back to top Mike Wahler Guest Posted: Fri Dec 17, 2004 2:45 am    Post subject: Re: Tracking information in input stream "Adam H. Peterson" <ahp6 (AT) email (DOT) byu.edu> wrote Quote: Instrumenting all the I/O routines I use reduces their encapsulation and makes them harder to read, and I believe it would be error prone. If the stream object can be made to track that information for me internally, it would (I believe) just work. Now that you've elaborated upon what you want, I see my advice is probably not applicable. See Jonathon T.'s reply. -Mike Back to top Jeff Flinn Guest Posted: Fri Dec 17, 2004 12:50 pm    Post subject: Re: Tracking information in input stream Adam H. Peterson wrote: Quote: Great. I love Boost and use it all the time, so I'll surely look into it. Are there any facilities in Boost 1.32 that I might be able to use to this effect? And/or do you have a good guess as to when the next Boost will be out? I'm succefully using Jonathan's IOStream library with boost 1.32 now (and have used it with 1.31 also). It's just a matter of copying to the appropriate directories. Jeff Back to top Adam Peterson Guest Posted: Fri Dec 17, 2004 4:39 pm    Post subject: Re: Tracking information in input stream Jeff Flinn wrote: Quote: I'm succefully using Jonathan's IOStream library with boost 1.32 now (and have used it with 1.31 also). It's just a matter of copying to the appropriate directories. My copy of boost is installed through RPM and I'd rather not mess with the package management system. Can I use the library without installing it in the same directory tree as boost? Back to top Jeff Flinn Guest Posted: Fri Dec 17, 2004 5:20 pm    Post subject: Re: Tracking information in input stream Adam Peterson wrote: Quote: Jeff Flinn wrote: I'm succefully using Jonathan's IOStream library with boost 1.32 now (and have used it with 1.31 also). It's just a matter of copying to the appropriate directories. My copy of boost is installed through RPM and I'd rather not mess with I've no idea what RPM is. Quote: the package management system. Can I use the library without installing it in the same directory tree as boost? Someone with more boost.build knowledge would have to answer that. Sorry, Jeff Back to top Jonathan Turkanis Guest Posted: Fri Dec 17, 2004 5:26 pm    Post subject: Re: Tracking information in input stream Adam Peterson wrote: Quote: Jeff Flinn wrote: I'm succefully using Jonathan's IOStream library with boost 1.32 now (and have used it with 1.31 also). It's just a matter of copying to the appropriate directories. My copy of boost is installed through RPM and I'd rather not mess with the package management system. Can I use the library without installing it in the same directory tree as boost? Yes, you can. I'm sorry I didn't say this explicitly before. Unless you need to use memmory-mapped files, streams based on file descriptors or filters using zlib or libbz2, all you need to do is put boost-1.32.0 and the iostreams root directory in your include path. You reference the iostreams headers the same way you would ordinary boost headers, e.g.: #include <boost/iostreams/operations.hpp> If you want to use the components mentioned aboce which have a separate .cpp files, just add the .cpp files to your project, if you are using an IDE, or to your makefile, and define the preprocessor symbol BOOST_IOSTREAMS_NO_LIB. Best Regards, Jonathan Back to top Adam H. Peterson Guest Posted: Mon Dec 20, 2004 10:53 pm    Post subject: Re: Tracking information in input stream Jonathan Turkanis wrote: Quote: (This is just an illustration; the official version will be more efficient.) I would be interested to know when you have an official version available, by the way. Quote: It could be used as follows: #include <iostream #include #include I think this last should be "#include Quote: .... I'm using the library and the code, but I'm running into a buffering problem. I'll query the line count and it will be actually too high because the next several lines have already been processed but not handed back to the application. Is there a way to work around this glitch? Thanks for the help so far, Adam Peterson Back to top Jonathan Turkanis Guest Posted: Tue Dec 21, 2004 2:13 am    Post subject: Re: Tracking information in input stream "Adam H. Peterson" <ahp6 (AT) email (DOT) byu.edu> wrote Quote: Jonathan Turkanis wrote: (This is just an illustration; the official version will be more efficient.) I would be interested to know when you have an official version available, by the way. I'll email you when the next version is available. It won't be "official" until Boost 1.33 is released, but I will be adding it to Boost CVS soon. Quote: It could be used as follows: #include <iostream #include #include I think this last should be "#include boost/iostreams/filtering_stream.hpp>", no? Right. Quote: I'm using the library and the code, but I'm running into a buffering problem. I'll query the line count and it will be actually too high because the next several lines have already been processed but not handed back to the application. Is there a way to work around this glitch? I believe if you set the buffer size to zero when you add the filter, you should get the actual number of lines read: filtering_istream in; in.push(line_counter(), 0); in.push(cin); Please let me know if this works, including whether it slows things down too much. Quote: Thanks for the help so far, Adam Peterson Jonathan Back to top Adam Peterson Guest Posted: Tue Dec 21, 2004 6:10 am    Post subject: Re: Tracking information in input stream Jonathan Turkanis wrote: Quote: I'm using the library and the code, but I'm running into a buffering problem. I'll query the line count and it will be actually too high because the next several lines have already been processed but not handed back to the application. Is there a way to work around this glitch? I believe if you set the buffer size to zero when you add the filter, you should get the actual number of lines read: filtering_istream in; in.push(line_counter(), 0); in.push(cin); Please let me know if this works, including whether it slows things down too much. That appears to work fine. I'm not noticing any performance difference, and I wasn't really expecting one either. I think buffering only makes a difference when interfacing with block I/O devices, so by the time you get past the original stream source it probably wouldn't help you any. In any event, I think any performance loss for my purpose(s) would be par for composing an alternate solution. FYI, I get some warnings when I compile: /.../boost/iostreams/categories.hpp:102: warning: virtual base `boost::io::input_seekable' inaccessible in `boost::io::iostream_tag' due to ambiguity /.../boost/iostreams/categories.hpp:102: warning: virtual base `boost::io::device_tag' inaccessible in `boost::io::iostream_tag' due to ambiguity /.../boost/iostreams/categories.hpp:102: warning: virtual base `boost::io::output_seekable' inaccessible in `boost::io::iostream_tag' due to ambiguity They look like design warnings for choices not likely to be made, but I thought I'd pass them along anyway in case you care. 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