February 2008 - Boost-users

[mpl] integral constant overflow
by klaus triendl 11 Mar '08

11 Mar '08

Hi, I've recently started studying the book "c++ template meta programming" (I like it a lot!) and one of my own exercises was to get an integral type's max/min value. To get the type's maximal value I've created a metafunction max_val; Compiling the code below with vc++2008 warning level 2+ yields the warning "truncation of constant value" or "integral constant overflow" if I use an int instead of a char. <code> namespace mpl = boost::mpl; template<typename T> struct significant_bits: mpl::int_<std::numeric_limits<T>::digits> {}; template<typename T> struct max_val_impl: mpl::accumulate< mpl::range_c<int, 1, significant_bits<T>::value>, mpl::integral_c<T, 1>, mpl::next<mpl::plus<mpl::_1, mpl::_1> > > {}; template<typename T> struct max_val: max_val_impl<T>::type { BOOST_MPL_ASSERT((boost::is_integral<T>)); }; int main() { const char maxval = max_val<char>::value; return 0; } </code> The problematic metafunction instantiation boils down to mpl::integral_c<char, 127> where mpl::integral_c<char, 127>::next results in 128 which is then truncated. Of course I can turn off the compiler warnings but since the warning happens in integral_wrapper.hpp and the integral constant stuff is included in many other files including the boost type traits it would be tedious to always remember to include integral_c.hpp explicitly before any other headers with the warnings turned off. I don't know whether there is a really satisfying option, just wanted to discuss this point. Klaus Triendl

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[thread] Priority?
by Ovanes Markarian 10 Mar '08

10 Mar '08

Hello, I used boost thread library a lot and like it very much. Currently, I was reading the C++ Standerd proposal and saw that a thread (as well as boost::thread) does not have a priority. Which reason was it not to implement the thread priority in boost, and why is it not considered in the upcoming standard? I understand this feature is rarely required, but if someone suddenly needs to start a real-time priority thread he/she will be forced to use a third party lib again. Or is there smth. what I miss? Many thanks, Ovanes

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boost exceptions on MacOS 10.5
by Lothar May 09 Mar '08

09 Mar '08

Hi, I've brought this up before, but I still have no solution for this issue, so I will give it another try: Does anyone have boost 1.34.1 compiled on MacOS 10.5 where exceptions can be caught? You might use the following code to test: --cut here-- #include <iostream> #include <boost/filesystem.hpp> using namespace std; using namespace boost::filesystem; int main() { try { directory_iterator i("does_not_exist"); } catch(...) { cout << "This is never printed on MacOS 10.5." << endl; } return 0; } --cut here-- If this works with your installation of boost on MacOS 10.5, please tell me which steps you did to compile boost, and whether you used the static or dynamic version. A related question is: Is boost "supposed to work" on MacOS 10.5? Thanks, Lothar

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ASIO: ssl - load_verify_file
by j.c. 07 Mar '08

07 Mar '08

Hello, I have implemented a TLS client/server application and will be using self-assigned certificates due to the small scale of distribution. I am currently using the function load_verify_file("ca.pem"), however I don't want to write the certificate to end-users disk. What would be the proper way to use an "in-memory or compiled" certificate for peer verification? Thanks, JC

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[regex] Question about pattern
by office＠mgs.co.at 06 Mar '08

06 Mar '08

Hi; I'm a newbie to regex patterns and need help in a relative simple task: I use boost::regex with perl syntax and I have to parse user input that provides a feature similar to the conditional formatting of cells in OpenOffice Calc. The string the user enters looks like this: >=30 [fg:red] [bg:white] or <0.0 [fg:none] [bg:transparent] First the user can enter an optional operator (> < <> = <= >=) followed by a integer or floating point number. This whole term is optional so [fg:red] [bg:white] is also a valid expression. The terms for color selection are partly optional, so valid expressions are [fg:red] or [bg:white] or [fg:red][bg:white] or [bg:white][fg:red] The key words for foreground and background colors are predefined by the software (red, green, blue, transparent, none, ...). I tried starting with a pattern like (C++ syntax for strings) ^(?:(<|<=|>|>=|=|<>){1}((?:-|\\+)?[0-9]+(?:\\.[0-9]+|\\,[0-9]+)?))?(?:\\s*)(?:(\\[FG:(?:BLUE|RED|GREEN|BLACK|YELLOW|WHITE|CYAN|NONE)\\])|(\\[BG:(?:BLUE|RED|GREEN|BLACK|YELLOW|WHITE|CYAN)\\])|(\\[FG:(?:BBLUE|RED|GREEN|BLACK|YELLOW|WHITE|CYAN|NONE)\\])(?:\\s*)(\\[BG:(?:BLUE|RED|GREEN|BLACK|YELLOW|WHITE|CYAN)\\])){1}$ But this does not allow the [fg:][bg:] terms to be interchanged and also when a new color or style will be added to the format class I have to change the pattern three times. I tried backward references with no success. So any help is very welcome Thanks in advance Martin

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including boost/thread.hpp gives compile error under VS7 in utility\base_from_member.hpp
by jason72＠internode.on.net 06 Mar '08

06 Mar '08

Using Visual Studio 2003 (VS7) and boost 1.34.1, I have simply declared the following code and I get the resulting errors: Code: #pragma once #include <deque> #include <boost/thread.hpp> using namespace std; <SNIP> Compiler output: cl /c /W3 /G6 /GF /Gy /nologo /DNDEBUG /DWIN32 /D_WIN32 /D_WIN32_WINNT=0x0500 /DWINVER=0x0500 /D_WIN32_IE=0x060 0 /D_AFXDLL /D_WTL_NO_CSTRING /D_WTL_NO_WTYPES /D_WTL_NO_UNION_CLASSES -D_X86_=1 /Ox /Z7 /I\src\r870\develop\work\pcd m\std\include /DNT /Dpcdm /DDBREL=870 /D_WIN32_DCOM -GX /DREGISTER_PROXY_DLL /GR /EHsc /MD /Fohtsserver.obj htsserver.cpp.cpp htsserver.cpp.cpp c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2143: syntax error : missing ',' before 'constant' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(78) : see reference to class template instantiation 'boost::base_from_member<MemberType,UniqueID>' being compiled c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2226: syntax error : unexpected type 'T0' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2334: unexpected token(s) preceding ':'; skipping apparent function body c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2143: syntax error : missing ',' before 'constant' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2226: syntax error : unexpected type 'T0' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2334: unexpected token(s) preceding ':'; skipping apparent function body c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2143: syntax error : missing ',' before 'constant' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2226: syntax error : unexpected type 'T0' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2334: unexpected token(s) preceding ':'; skipping apparent function body c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2143: syntax error : missing ',' before 'constant' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2226: syntax error : unexpected type 'T0' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2334: unexpected token(s) preceding ':'; skipping apparent function body c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2143: syntax error : missing ',' before 'constant' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(76) : error C2226: syntax error : unexpected type 'T0' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(78) : error C2143: syntax error : missing ';' before '}' c:\apps\boost_1_34_1\boost\utility\base_from_member.hpp(78) : error C2238: unexpected token(s) preceding ';' c:\apps\VS .NET 2003\Vc7\include\ostream(604) : fatal error C1903: unable to recover from previous error(s); stopping compilation NMAKE : fatal error U1077: 'cl' : return code '0x2' Stop. Note that I havent declared or used any of the threading or mutex objects yet. It is not possible to upgrade compiler version for this project. Regards, Jason

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[iostream] Overloaded bitshift operators
by Robert Dailey 05 Mar '08

05 Mar '08

Does the Boost.Iostreams library have overloaded bitshift operators? That way I could do: boost::iostreams::stream<myclass> theOutputStream; theOutputStream << MyData;

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[iostreams] Inconsistency b/w docs and code of stream()
by Nitay Joffe 05 Mar '08

05 Mar '08

>> > Nitay Joffe wrote: >> > Hey guys, >> > >> > I'm working with the boost::iostreams library to create a stream object >> > from >> > a Device class I've implemented. I'm trying to call the constructor that >> > allows setting of the buffer size and it is failing to compile on 64 bit. >> > >> > I used the documenation at >> > http://www.boost.org/libs/iostreams/doc/guide/generic_streams.html#stream >> > >> > The docs say the constructor is of the form: >> > >> > stream(const T& t, >> > std::streamsize buffer_size = default_value, >> > std::streamsize pback_size = default_value); >> > >> > >> > My code to create the stream looks like: >> > >> > MyDevice myDevice(...) >> > MyStream(myDevice, (std::streamsize)500); >> > >> > >> > On a 32 bit machine this works fine, but on a 64 bit one it does not >> > compile. The parameters I'm passing in are not matching up with a > > Would you please post the compiler errors? > >> > Thanks, >> > -n Sure, here is sample code that causes the error: #include <iosfwd> #include <boost/iostreams/categories.hpp> #include <boost/iostreams/stream.hpp> struct MyDevice { typedef char char_type; typedef boost::iostreams::source_tag category; std::streamsize read(char *s, std::streamsize n) { return n; } }; typedef boost::iostreams::stream<MyDevice> MyStream; int main() { MyDevice d; MyStream s(d, (std::streamsize)500); return 0; } And here are the compile errors: g++ a.cc k/usr/include/boost/iostreams/stream.hpp: In constructor 'boost::iostreams::stream<Device, Tr, Alloc>::stream(U100&, const U0&) [with U100 = MyDevice, U0 = std::streamsize, Device = MyDevice, Tr = std::char_traits<char>, Alloc = std::allocator<char>]': a.cc:18: instantiated from here /usr/include/boost/iostreams/stream.hpp:110: error: no matching function for call to 'MyDevice::MyDevice(MyDevice&, const long int&)' a.cc:5: note: candidates are: MyDevice::MyDevice() a.cc:5: note: MyDevice::MyDevice(const MyDevice&) make: *** [all] Error 1 If I change the (std::streamsize) to (int) it compiles. Cheers, -n

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[foreach][range] How would BOOST_REVERSE_FOREACH be implemented?
by Pete Bartlett 05 Mar '08

05 Mar '08

Boost.Foreach is such a great piece of kit that once you start using it you just can't stop. Indeed I like working directly with values rather than iterators so much that is feels normal for me to write something like BOOST_FOREACH( value_type x , make_iterator_range( rbegin( seq ) , rend( seq ) ) whenever I wish to reverse iterate over a sequence. My co-workers are not big fans of typing though, so they want a REVERSE_FOREACH. At first naïve glance it looks easy to implement in terms of the original FOREACH: template<typename C> inline iterator_range</* something */> make_reverse_iterator_range(C& c) { return make_iterator_range( rbegin(c) , rend(c) ); } #define REVERSE_FOREACH( x , container ) BOOST_FOREACH( x , make_reverse_iterator_range( container ) ) This works fine when container is an lvalue. But then co-workers, used to the wonders of the original FOREACH, inevitably start to use the new macro with rvalues and get a crash due to dangling references (- the iterator_range's members point to departed quantities.....) and if you could somehow work around that, there is the issue hidden inside the "/* something */" that you have to cope with fact that MSVC has no proper const rvalue detection. Finally the #define MACRO(x,y) ANOTHER_MACRO( f(x) , g(y) ) style is not recommended because they are brittle in the face of x and/or y themselves being macros. ... but all these issues are exactly the ones that BOOST_FOREACH itself solves! Thus surely it is technically possible to write a REVERSE_FOREACH that works with rvalues as well as lvalues, e.g. by essentially copying and pasting the FOREACH implementation and replacing "begin" and "end" by "rbegin" and "rend" in the vital places. However one feels there may be a better way... has anyone had a go at creating a "fully-functional" REVERSE_FOREACH and could offer me any advice? If indeed the task is fairly intricate and requires re-use of foreach internals, would the library author consider including something in the library itself? Many thanks for reading, Pete Bartlett

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Ann: Floating Point Utilities Review starts today
by John Maddock 04 Mar '08

04 Mar '08

The review of Johan Rade's floating point utilities starts today. Code and docs can be downloaded from : http://www.boost-consulting.com/vault/index.php?action=downloadfile&filenam… The library consists of three parts: 1) Floating point classification routines: these are optimised implementations of the C99 and C++ TR1 functions fpclassify, isinf, isnan, isnormal and isfinite. From Boost-1.35 onwards these are already a part of Boost.Math (see http://svn.boost.org/svn/boost/trunk/libs/math/doc/sf_and_dist/html/math_to…) so if accepted the two implementations will get merged. The review here should focus on the implementation used, and testing on whatever platforms you have available - in particular are there any circumstances (compiler optimisation settings etc) where this implementation breaks? 2) Sign manipulation functions: implementations of the C99 and C++ TR1 functions copysign and signbit, plus the changesign function. Two of these (signbit and copysign) are currently undocumented members of Boost.Math, and again the two implementations will get merged if this library is accepted. Again the main focus of the review here is the implementation, and testing thereof especially in the presence of compiler optimisations. 3) C++ locale facets: these will read and write non-finite numbers in a portable and round-trippable way: that is not otherwise possible with current C++ std library implementations. These are particularly useful for number-serialisation for example. Since the design is already specified by the C++ standard for these facets, your review here should focus on implementation, testing, documentation, and perhaps where in Boost these should best be placed if accepted. These look to be a useful collection of utilities, so I'll look forward to your reviews, Regards, John Maddock, Floating Point Utilities Review Manager.

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