October 2010 - Boost-users - lists.preview.boost.org

[asio] How to get informed about failed connection attempts?
by for-gmane 10 Oct '10

10 Oct '10

The following code (from the examples) accepts a connection and calls the handler handle_accept(). But it calls the handler only if the connection attempt (internally) succeeds. The handler gets not called if the connection fails (for example when an ssl-connection-attempt fails due to wrong keys etc.). What should I do to get informed also about such failed connection attempts? acceptor_.async_accept(new_session->socket(), boost::bind(&server::handle_accept, this, new_session, boost::asio::placeholders::error));

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Memory usage
by Olivier Tournaire 10 Oct '10

10 Oct '10

Hi all, Is there a (portable) way with boost libs to check memory usage? Best regards, Olivier

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Http Server 3 example with SSL, ie. https
by for-gmane 09 Oct '10

09 Oct '10

Hi, has anybody extended the Http Server 3 example with SSL, ie. https? Are there any other simple https-server examples based on asio?

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AIX large file support
by Will Mason 09 Oct '10

09 Oct '10

Hello, I'm using Boost 1.42, IBM XL C++ 10.1, and AIX 5.3. On AIX the way to enable large file support is to define _LARGE_FILES on the compiler command line. When I attempt to build Boost with this definition, I see errors like the following: "/home/wmason/src/cap-aix/fim/../opt/include/aix/boost/v1.42/boost/date_time/date_parsing.hpp", line 50.21: 1540-0215 (S) The wrong number of arguments have been specified for "tolower(int)". This causes catastrophic failure of Boost to build. Fortunately, by poking around the sources I found that I can enable large file support in Boost on AIX with IBM's compiler by defining _LARGEFILE64_SOURCE. Although this bypasses IBM's recommended way of enabling large file support, it does work to build Boost with large file support. The problem is that my product enables large file support the normal way, which leads me back to the above error when I try to build. I could just manually enable large file support in my code, but this causes portability problems. Not all operating systems support large files the same way, so trying to do it manually on every system will be a headache. Our portability strategy involves enabling large file support the normal way on every system, which in many cases, including AIX's, involves defining things on the command line. Is there any way to use normal large file support on AIX and not have Boost go down in flames? Thanks very much for any help, Will

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[proto] Can't use template domain class with BOOST_PROTO_BASIC_EXTENDS
by joel falcou 09 Oct '10

09 Oct '10

Trying to use template domain class with BOOST_PROTO_BASIC_EXTENDS ends up in an error leading to the fact this ligne in the macro is incorrect when the Domain is template: BOOST_PROTO_BASIC_EXTENDS_(Expr, Derived, Domain) typedef void proto_is_aggregate_; typedef Domain::proto_generator proto_generator; Obviously this is alckign a typename before Domain::proto_generator if Domain is actually a template class. Thing is used to work before ( aorund 1.40) so I guess somethign changed around here. I guess a details meta-function extracting the domain will fix that or am I wrong ? namespace boost { namespace proto { template<class Domain> generator_of { typedef typename Domain::proto_generator type; }; } } BOOST_PROTO_BASIC_EXTENDS_(Expr, Derived, Domain) typedef void proto_is_aggregate_; typedef typename generator_of<Domain>::type proto_generator; Or is it ?

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[variant][any] template parameterized variant
by alfC 09 Oct '10

09 Oct '10

Hi, I need a variant type object that can hold any type characterized by a template. For example Boost.Units have a family of types parameterized by "System". quantity< unit<dimension, System>, double> suppose dimension is fixed, e.g. typedef boost::units::length dimension is it possible to define a variant over that family of types? I could create a make_variant_over< list of all types > but that can be that list will be fixed and each time I defined a new System the list will have to grow. to simplify the question: template<class T> class dummy{ ... }; variant< "dummy<T>" > v; //for all T If it simplifies things, suppose that all dummy<T> have the same sizeof and that all are convertible to each other. Or should I be using an extension of boost::any with some adhoc restriction over the possible types on construction? Thank you, Alfredo

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[fusion] .at<N>() template member in containers?
by alfC 09 Oct '10

09 Oct '10

Hi, Excuse my simple minded questions. Sometimes by asking this question (often with negative answer) I understand more on the design of the Boost libraries. Besides possible redundancy, why is that the fusion containers, for example fusion::vector, doesn't have a template member function to extract elements? fusion::vector<double, int, std::string> stuff(1.2, 3, "hola"); stuff.at<2>(); //returns "hola", just like at_c<2>(stuff); Wouldn't it be more consistent with std::vector v, v[2] or v.at(2); By the way, does anybody know where the name given "at_c" (I mean the '_c') comes from? Thank you, Alfredo

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boost/preprocessor checking if argument is a constant
by Z S 09 Oct '10

09 Oct '10

All the BOOST_PP functions only work on integer constants. I want to write macros, where the same interface can be used for both constants and variables, and only call the BOOST_PP if the argument is a constant, and use runtime code if it is a variable. For example, #define TWICE(n) BOOST_PP_IF( _IS_CONSTANT(n), \ BOOST_PP_MUL(n,2), \ ( (n) * 2) ) For more details, you can also see the original question here : http://stackoverflow.com/questions/3884489/mixing-variables-and-integer-con… Is there a way to do so? The C preprocessor knows whether something is a constant, so we should be able to do this somehow. Or should I suggest this as a feature request for the Boost Preprocessor library? Thanks!

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Re: [Boost-users] Boost Logos: proposed high constrast logo
by Zoltan Juhasz 08 Oct '10

08 Oct '10

Follow up on the original topic: I've uploaded a high-contrast version of the Boost Logo, and moved all other logo related resources to the follow Google Docs folder: https://docs.google.com/leaf?id=0B_WA6oW88X1UZWZiNzUwYzctYzg1NS00ZmY5LTllMD… On the logo discussion: Various explanation could be made for the logo. For some these are molecular structures; for others this is a small matrix of hexagonal cells from a beehive; some may claim these are interconnected - in some places overlapping - software components etc. Probably all of these seem reasonable, maybe non of these for someone. My point is that one could come up with any justification for the hexagons, but it will not change others mindset on it. On the other hand... ... this is an abstract logo, which is fairly simple (well at least the stylized form), it does not bring any cultural or any specific technology connotations, and most importantly provides / provided a "face" for Boost in the last 4 (or 5?) years. This is a strong connection in public mind between the Boost community and the logo; where the previous one defines the later - which (the community, and the Boost project) has excellent reputation, which made the logo highly recognizable (like any famous company brand). The point is, it is not the logo which defines Boost, but the other way around. Ofc. if the logo was something like this: http://preview.tinyurl.com/2wcg757 that would be arguably a big deflection compared to the spirit of Boost, but I do not think this applies to the current case (chemical analogy). The other important point is that most of the developers that used Boost in the previous years, already made the connection between the logo and the Boost Libraries; making a radical change might be a bad idea, unless there is a really strong reason to do that (for example Boost ceases using C++, and focusing on Objective C from now), otherwise keeping the continuity is important. I hope the high contrast version of the logo is usable, let me know if you need further help with it. I also hope that I was able to give you some background on the abstract hexagons. Regards, Zoltan Juhasz

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[proto] baby steps learning with proto, proxy object
by alfC 08 Oct '10

08 Oct '10

Hi, This can be an exercise for definining the scope of Boost.Proto for little things. I have a histogram class that internally looks like this class histogram{ ... bool operator()(double const& x){return impl.increment(x);} bool operator()(double const& x, double const& weight){return impl.accumulate(x, weight);} }; histogram h( .. bin spec .. ); double x = ... ; so to add a count to the bin of x, I call h(x); to add a count with weigh w to bin x, I call h(x,w); so far so good. Now suppose I want to "improve" the syntax. The desired syntax would be: h[x]++; h[x]+=w; I don't want to expose the internal representation of the bins, so I can't return a reference to something from h[x]. So I guess we can create a proxy of the expression h[x] , "subindex of historgram with double". The proxy can be used with the syntax to call either accumulate or increment depending on the application of += or + + to the proxy. The naive implementation is this: class histogram{ ... private: struct proxy_histogram_subscript{ histogram& self; double const& x; proxy_histogram_subscript(histogram& self, double const& x) : self(self), x(x){} proxy_histogram_subscript const& operator++() const{self.increment(x); return *this;} bool operator++(int) const{return self.increment(x);} bool operator+=(double const& weight) const{return self.accumulate(x, weight);} }; public: proxy_histogram_subscript operator[](double const& x){ return proxy_histogram_subscript(*this, x); } }; which allows the desired syntax. The question is, can Boost.Proto do better? What I don't understand is how proto can make such a mini language *inside* the class. Hopefully without adding to much lines of code. I can see that one could create a histogram terminal, but that will be public (e.g. from the main program) and that will allow to create all sorts of expression involving brackets of anything. Thank you, Alfredo

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