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[interprocess] garbage chars when extending interprocess strings?
by Anthony Foiani 01 Aug '11

01 Aug '11

I'm having a peculiar problem with interprocess strings. 0. Create the shared string type. typedef boost::interprocess::managed_shared_memory ShmManagerType; typedef char ShmCharType; typedef boost::interprocess::allocator< ShmCharType, ShmManagerType::segment_manager > ShmCharAllocatorType; typedef boost::interprocess::basic_string< ShmCharType, std::char_traits< ShmCharType >, ShmCharAllocatorType > ShmStringType; 1. Initial write succeeds. ShmStringType val; val = "x"; cout << quoteString( x ) << endl; // prints "x" as expected 2. When I overwrite the value with a longer value, the longer value is stored and the length is updated -- but a null character (\0) is inserted at the *old* length. ShmStringType x3( "xxx" ); val = x3; cout << quoteString( val ) << endl; // prints "x\0x" !!! 3. When I write the longer value again, it is stored correctly and there is no \0 in the middle of the string. val = x3; cout << quoteString( val ) << endl; // prints "xxx" as expected 4. The same thing happens if we try a longer value again: ShmStringType x5( "xxxxx" ); val = x5; cout << quoteString( val ) << endl; // prints "xxx\0x" val = x5 cout << quoteString( val ) << endl; // prints "xxxxx" Does this ring bells for anyone? On my embedded platform, I'm using: powerpc e300c3 Linux 2.6.36 eglibc 2.13 boost 1_44_0 g++ 4.5.1 And on my development workstation: intel x86-64 Linux 2.6.35.13-92.fc14 glibc 2.13-1 boost 1.44.0-8.fc14 gcc 4.5.1-4.fc14 Testing this on my development workstation, I see similar issues (although it's not always \0; in this case, I'm getting \xC0 junk characters. Odd!) Test case at: http://foiani.com/cpp/boost/InterProcStringTest.cpp Sample output: http://foiani.com/cpp/boost/ipst-out-ppc32.txt http://foiani.com/cpp/boost/ipst-out-x86_64.txt The output isn't the same: some cases work on one platform but not the other, and the garbage character introduced isn't always \0. Any ideas would be welcome. Testing with a more current boost is a bit problematic; if someone believes that it's been fixed in the mean time, I'll do my best to try with a modern boost. In the mean time, I'll just write the values twice, I guess. :) Thanks for your time and attention! Best regards, Tony

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[Iterator]Can dereference() in iterator_adaptor return a temporary value?
by Remi 01 Aug '11

01 Aug '11

Hi, I'd like a const iterator that acts as a proxy by giving access to elements of type A as if they were elements of unrelated type B. In that case I guess the dereference() member function should return a temporary value, right? Would that be a correct implementation of the idea? Here I just want to access an array of SourceVertexType as if it were an array of VertexType. template<class VertexType> class ConstVerticesIterator : public boost::iterator_adaptor< ConstVerticesIterator<VertexType>, const SourceVertexType*, const VertexType > { private: friend class boost::iterator_core_access; VertexType dereference() const { const SourceVertexType& source_vertex( *base() ); return VertexType( source_vertex.x, source_vertex.y ); } public: explicit ConstVerticesIterator( const SourceVertexType* vertices ) : boost::iterator_adaptor< ConstVerticesIterator<VertexType>, const SourceVertexType*, const VertexType >( vertices ) {} };

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translate C-code into objects
by Peter Foelsche 01 Aug '11

01 Aug '11

Dear All, I would like to translate some C-Code into objects. I did this already for functions and expressions: Writing template functions and passing my expression object as an argument. Now I want to do this for C-Code, which uses if-statements and variables. To do this, I would implement some template function for an if-statement. And some function for an assignment to a variable. Probably using enumerations to indicate the variable. Is this the right approach? Peter

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[foreach] Changes in Boost 1.47 beaking const rvalue detection for some compilers?
by Joaquin M Lopez Munoz 31 Jul '11

31 Jul '11

Hi, According to the discussion at http://lists.boost.org/boost-users/2011/07/69718.php seems like for some non-copyable sequence types, such as indices of Boost.MultiIndex, Boost.Foreach has stopped in GCC 4.6.1 with Boost 1.47 (and did not work in clang++ 2.9 either for Boost 1.46 or Boost 1.47.) Before I apply the boost::foreach::is_noncopyable hack, can the author take a look at this? Release notes for Boost 1.47 indicate that const rvalue detection has been modified in Boost.Foreach, so I wonder whether this situation is something that should be fixed in Boost.Foreach rather than user code. Thank you, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

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[Serialization] Segmentation fault in split load
by Aditya Gadre 31 Jul '11

31 Jul '11

Hi, I am using Boost::Serialization to save and load a custom class using binary archive. I have split save and load functions as I need to do some initialization during loading process. However, I am getting a segmentation fault while loading and I am not very sure of the reason. The segmentation fault occurs while loading a boolean. I would appreciate any help in this regard. I have attached a full back trace and also the header file for the custom class. Thanks, - Aditya

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[units] quantity to/from string / setting value component apart from the units
by Michael Powell 31 Jul '11

31 Jul '11

Units developers/user, Preferably, I would like to get after a quantity's value and/or its units in string format, plumb that through to the .NET Managed environment. The managed plumbing is straightforward enough to research, no problem. Can I use boost::units::to_string(q), where q is declared something like quantity<si::length,float>? And then, what can we expect after calling it? For instance, if q is set to 2.5 * meters, then can we expect "2.5 m"? Also, can I set a quantity value apart from its unit? In other words, if I've got a quantity<si::length,float> q again, I'd like to do something like this: q.value(2.5); or: q = 2.5; Or some way that preserves the current quantity units. Thank you... Regards, Michael

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DateTime from String
by Kraus Philipp 31 Jul '11

31 Jul '11

Hello, I read a string with a date / time format, like: Fri, 29 Jul 2011 13:48:57 +0000 Can I use Boost.DateTime to convert the string into a std::time_t value? How can I do this? Thanks Phil

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asio problem with detecting http header end
by Kraus Philipp 31 Jul '11

31 Jul '11

Hello, I use Boost.ASIO for receiving Twitter JSON data. I use this code: boost::asio::write( p_socket, l_request ); boost::asio::streambuf l_response; boost::asio::read_until(p_socket, l_response, "\r\n\r\n"); So in my optional the l_response variable should be read the full HTTP header. But if I write it to the std::cout I get: HTTP/1.1 200 OK Date: Fri, 29 Jul 2011 20:08:37 GMT Server: hi Cache-Control: max-age=15, must-revalidate, max-age=300 Expires: Fri, 29 Jul 2011 20:13:37 GMT Content-Type: application/json;charset=utf-8 Content-Length: 9763 Vary: Accept-Encoding X-Varnish: 1045274856 Age: 0 Via: 1.1 varnish X-Cache-Svr: smf1-aba-35-sr2.prod.twitter.com X-Cache: MISS Connection: close {"completed_in":0.025,"max_id":97033383951081472,"max_id_str":"97033383951081472","next_page":"?page=2&max_id=9703338395108147 I can change the "until read parameter" to \n, Connection: close or something else, but the read_until method does not stop the reading at the correct chars. Same code on a Wikipedia call runs without problems. Can anyone help me please to receive the correct header? Thanks Phil

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by Lars Schouw 31 Jul '11

31 Jul '11

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[units] build up a runtime
by Michael Powell 31 Jul '11

31 Jul '11

Units developers/users, I need some advice. I am fairly confident boost::units is the way for us to go and support a design- or compile-time unit safe calculations environment. However, now for the tricky business of exposing that functionality to the rest of our application. I am in the midst of trying to do this by exposing some Managed C++ classes, plausibly representing each kind of dimension; to get started with I implemented a base Quantity class, and I am extending that to a Length. I would like to include a quantity<si::length> member, for starters, but I am receiving a build error: Error 2 error C4368: cannot define 'si_l' as a member of managed 'CS::Boost::Units::Dimensions::Length': mixed types are not supported c:\source\safetyvalve2011\cs.calculations.managed\units\Length.h 41 CS.Calculations.Managed This might extend to include a quantity<us::length>, for instance; and so on for other unit systems. Whatever .NET class we expose, this will act like the proxy between the application layer and the calculations layer; we might have Dimension-aware UI controls that work on Length, or Quantity, for instance. That sort of thing. Anyone encountered anything like this before? Or have suggestions how we might overcome this hurdle? I'm puzzling this one through in the meantime... Thank you... Regards, Michael

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