July 2003 - Boost-users - lists.preview.boost.org

Spirit Parsing Problem
by sps22 31 Jul '03

31 Jul '03

Hi, I am trying to use Spirit (in the latest Boost 1_30_0) for a project. I want to parse a file whose structure is the following: section1 { something; } I am using the file_iterator to iterate on the input file and then define comment as well as the grammar. I am at my wits end why my parser keeps failing. (When this simple grammar works, I want to make the parser more complex.) My code is attached below. (Note: I used the example in the distribution c_grammar.cpp as the starting point for it.) Thanks. -surinder PS: This input file structure is going to be, of course, more complicated than the example shown above. Inside the setions, I would like to pass on flags and statements to the code. If it is better for me to use another approach to parse this file structure, please suggest me. #include <iostream> #include <fstream> #include <vector> #include <boost/spirit.hpp> /* Input file for this looks like: file { something; } */ ////////////////////////////////////////////////////////////////////// ///////// // used namespaces using namespace boost::spirit; using namespace std; ////////////////////////////////////////////////////////////////////// ///////// // parsing helper function // Here's our comment rule struct skip_grammar : public grammar<skip_grammar> { template <typename ScannerT> struct definition { definition(skip_grammar const& /*self*/) { skip = space_p | comment_p("//") // C++ comment | comment_p("/*", "*/") // C comment | comment_p("#") // added for correctly ; } rule<ScannerT> skip; rule<ScannerT> const& start() const { return skip; } }; }; ////////////////////////////////////////////////////////////////////// ///////// // typedef typedef char CharT; typedef file_iterator <CharT> IteratorT; typedef scanner <IteratorT> ScannerT; typedef rule <ScannerT> RuleT; template<typename GrammarT> void parse(GrammarT const& g, char const* filename) { ifstream in(filename); if (!in) { cerr << "Could not open input file: " << filename << endl; return; } IteratorT start(filename); if (!start) { cerr << "Could not open the file " << endl; return ; } IteratorT end = start.make_end(); skip_grammar skip; parse_info<IteratorT> result = parse(start, end, g, skip); if (result.full) cerr << filename << " Parses OK" << endl; else { cerr << filename << " Fails Parsing" << endl; for (int i = 0; i < 50; i++) { if (result.stop == end) break; cerr << *result.stop++; } cerr << endl; } } struct c_grammar : public grammar<c_grammar> { template <typename ScannerT> struct definition { definition(c_grammar const& /*self*/) : SEMICOLON(';'), COMMA(','), COLON(':'), ASSIGN('='), LEFT_PAREN('('), RIGHT_PAREN(')') { // C keywords keywords = "file", "physics", "math"; // C operators LEFT_BRACE = chlit<>('{') | strlit<>("<%"); RIGHT_BRACE = chlit<>('}') | strlit<>("%>"); LEFT_BRACKET = chlit<>('[') | strlit<>("<:"); RIGHT_BRACKET = chlit<>(']') | strlit<>(":>"); // Tokens FILE = strlit<>("file"); PHYSICS = strlit<>("physics"); MATH = strlit<>("math"); // string literals STRING_LITERAL_PART = lexeme_d[ !chlit<>('L') >> chlit<>('\"') >> *( strlit<>("\\\"") | anychar_p - chlit<>('\"') ) >> chlit<>('\"') ] ; STRING_LITERAL = +STRING_LITERAL_PART; // Rules file_statement = FILE >> LEFT_BRACE >> *(anychar_p) >> RIGHT_BRACE; // does not work // file_statement = *(anychar_p); // parses OK translation_unit = file_statement; } symbols<> keywords; chlit<> SEMICOLON, COMMA, COLON, ASSIGN, LEFT_PAREN, RIGHT_PAREN; rule<ScannerT> LEFT_BRACE, RIGHT_BRACE, LEFT_BRACKET, RIGHT_BRACKET; rule<ScannerT> FILE, PHYSICS, MATH, STRING_LITERAL, STRING_LITERAL_PART; rule<ScannerT> file_statement, translation_unit; rule<ScannerT> const& start() const { return translation_unit; } }; }; ////////////////////////////////////////////////////////////////////// ///////// // main entrypoint int main(int argc, char* argv[]) { // Start grammar definition cerr << "C Grammar checker implemented with Spirit ..." << endl; // main driver code c_grammar g; if (2 == argc) parse(g, argv[1]); else cerr << "No filename given" << endl; return 0; }

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Re: [Boost-Users] Newbie shared_ptr in a container question.
by Joshua Little 31 Jul '03

31 Jul '03

>From: "Duane Murphy" <duanemurphy(a)mac.com> >Reply-To: Boost-Users(a)yahoogroups.com >To: "Boost Users" <Boost-Users(a)yahoogroups.com> >Subject: Re: [Boost-Users] Newbie shared_ptr in a container question. >Date: Sun, 27 Jul 2003 09:17:48 -0700 > >--- At Sat, 26 Jul 2003 19:57:17 +0000, Joshua wrote: > > >I've been reading through posts on here and in the docs but I think I may > >have missed something. Heres what I am trying to do: > >lets say I have a class Foo* and I'm trying to use it in a > >std::vector<shared_ptr<Foo> >. I can add them all day long and it works > >fine. The problem is that when I try to remove the shared_ptr from the > >vector. I expected it to delete the memory for the Foo* then delete > >itself (to completely free the memory that the shared_ptr used and the > >memory that the Foo was using. I think this is not happening though since > >the destructor is not being called when the elements are removed from the > >vector. Heres how I am currently inserting the shared_ptr's into the > >vector (yes I know this is the wrong way now that I've read a few of the > >posts here): > > > >typedef std::vector<boost::shared_ptr<Foo> > FooVector; > > > >FooVector Foobar; > >Foo* blah = new Foo(); > >boost::shared_ptr<Foo> * NewPointer = new boost::shared_ptr<Foo>(blah); > >Foobar.insert(*NewPointer); //Yes I know this looks horrible. And its > >probably wrong. > > > > > >When I call Foobar.erase() I thought that the shared_ptr would be removed > >and the memory freed (and Foo's destructor called). I tried it like this >: > >FooVector::iterator CurrentFoo = Foobar.begin(); > >Foobar.erase(CurrentFoo); > > > >That did remove the shared_ptr but the Foo* did not seem to get > >deallocated, its destructor was never called. Some of the posts seem to > >indicate that this is a very bad way to let shared_ptr manager the > >memory, is there a better way to do what I want to do using shared_ptr or > >is shared_ptr the wrong tool to use? > >There have been many good suggestions as to what the correct sequence for >inserting the shared_ptr into the vector. I'm not sure the real problem >has been adequately explained. Why isnt the foo* being deleted. > >Shared_ptr<> counts the number of instances of the pointer that are >created. When you did: > >boost::shared_ptr<Foo> * NewPointer = new boost::shared_ptr<Foo>(blah); > >You created the first instance; count == 1. > >When you did: > >Foobar.insert(*NewPointer); //Yes I know this looks horrible. And its > >A copy of the shared_ptr<> was made. The count is now 2. > >When you did: > >Foobar.erase(CurrentFoo); > >One copy (of two) was "deleted". In this sense, the shared_ptr<> was >deleted. The destructor for the shared counter mearly decrements the >counter. Count == 1. > >The problem is that the original count was leaked by using "new >shared_ptr<>". This is why all the suggestions show that you should be >using the stack based method for shared_ptr<>. > >Shared_ptr is almost never allocated from the heap. There really is not >much point. It's use is as a value representation of pointer. > >I hope this helps you understand where your code went astray. > >Good luck, > ...Duane > > > > > ...Duane > Reading many of these replys I now see why what I was doing wasn't working, so I'm going to change my code around and hopefully get this cleared up. Thanks to everyone for your help :) _________________________________________________________________ Add photos to your e-mail with MSN 8. Get 2 months FREE*. http://join.msn.com/?page=features/featuredemail

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Newbie: Way to convert "pointer-to-member-function" to a "pointer-to-function".
by Amit Bhatia 31 Jul '03

31 Jul '03

Hello All!, I am trying to figure out a way of converting "pointer-to-member-function" to a "pointer-to-function" so that I can pass it as a callback function pointer to constructor of some third party class. I know there is NO direct way of doing this in c++. I am further constrained because of the following facts: 1. The fact that I am using a third party class for whose constructor I need to pass pointers to functions having some specific signature. 2. I don't want to be using static declaration for the method that I wish to pass to the third party constructor as a callback function(due to the fact that static methods can access only access static data members). So if I am not mistaken, then, I suppose, that boost function library might be of help in here by somehow using some elegant tricks' to do this task. (There is the fact also that every instance of my class has lot of data which is different and I need access to the data for the method that I wish to pass). Am I right, or am I looking at the wrong place? If I am indeed looking at the wrong place then where will it be best to look for it. I remember some notes on binding in the documentation of the boost function library though. Thanks in advance, regards, amit.

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Detecting None in Boost.Python
by ahakim777 31 Jul '03

31 Jul '03

Hi, This is a Boost.Python question. How do I detect that a Python function has passed a 'None' to a wrapped C++ function? Cheers, Ammar

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filesystem::path & wide char strings?
by Cody Batt 30 Jul '03

30 Jul '03

Hello, I want to use the filesystem::path class for a project I'm working on, but I need to support wide character strings in the path names. I might be missing something, but it seems that path only supports std::string. Is this because of a portability issue or what is the rationale for not using something like basic_string<CharType>? Are there any plans to provide support for wide character strings in the future? Thanks, Cody Batt

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howto map c++ namespaces using boost::python?
by cavok＠filibusta.crema.unimi.it 30 Jul '03

30 Jul '03

hi all, i'm a newbie user of Boost. i need some suggestions to expose c++ namespaces in python. in python i use classes as namespaces, but using class_ construct to build python classes seems to not be applicable to c++ namesapces. moreover, i have a global c++ object which i'd like to map onto python. it is not that clear to me how i can achieve this result. thanks domenico -----[ Domenico Andreoli, aka cavok --[ http://filibusta.crema.unimi.it/~cavok/gpgkey.asc ---[ 3A0F 2F80 F79C 678A 8936 4FEE 0677 9033 A20E BC50

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Boost Bind on MSVC 7.1
by Dale Peakall 30 Jul '03

30 Jul '03

The following example is a very simple, and contrived, example that demonstrates the problem I'm seeing. This fails to compile with 'term does not evaluate to a function taking 1 arguments'. Is this a problem with bind on MSVC 7.1, or have I just forgotton how to use it/what it can do. - Dale. #include <iostream> #include <string> #include <boost/bind.hpp> int my_function(std::string const& value) { return static_cast<int>(value.length()); } int main() { std::string my_string("hello world!"); std::cout << boost::bind<int>(_1, my_string)(my_function); }

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boost.python exception
by newwz2003 29 Jul '03

29 Jul '03

Can I raise exception in C++ module can catch it in python ? or where can I get detailed doc about boost.python? Thank you

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Deferred Function Forwarding
by vivek_arora 29 Jul '03

29 Jul '03

I am looking for pointers on how to use boost to implement a set of template classes/helper functions which can be used for deferred function/method call forwarding. Here's an example of illustrating what I wish to accomplish. I can live with restictions on the function argument types. //Define a template type which can capture arguments of any (or most) functions. I believe boost tuple could suit my requirements. //Define a template helper function save_args which constructs a arguments tuple based on the signature of the function passed as the first argument. e.g . R f(T1, T2, T3); boost:tuple<R, T1, T2, T3> args = save_args(f, t1, t2, t3); //Don't want to explicitly specify types like save_args<R,T1,T2,T3> (t1,t2,t3) //Define another template helper function call_with_args which given another function "g" with a signature conforming with "f" and the argument tuple invokes "g" e.g. R g(T1, T2, T3) //This should call g(args.get<0>, args.get<1>, args.get<2>) call_with_args(g, args); Could someone provide ideas, pointers/sample code for implementing save_args, call_with_args helper template functions. Thanks -Vivek Arora

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Feature Suggestion
by everwicked 29 Jul '03

29 Jul '03

Hello guys, I have just been introduced to the library by some people at Efnet's #c++ and I have to say there is quite a lot of useful work in there. I hope boost makes it into the standard. It's about time to get a feature rich std library. Want I wanted to ask you is to provide a few more functions in library interval. I was comparing boost with blitz++ as the parts I need at the moment are mainly of scientific nature. Anyways, I found boost more to my likeness because it has other features I might want to use later, because it supports more compilers and lastly because it's API is better organised in my opinion. The functions that I find that are missing from library 'interval' are the ones listed here: http://www.oonumerics.org/blitz/manual/blitz03.html#l77 Is there any chance you could implement them in boost? I wouldn't ask but I think that they are not a lot of work. Thanks in advance. Kind regards, George

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