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RE: shared_ptr - implicit conversion to bool
by scleary＠jerviswebb.com 30 Jan '03

30 Jan '03

> From: wasekvesely <vaclav.vesely(a)volny.cz> > > I've found this in "shared_ptr.hpp": > > // implicit conversion to "bool" > typedef T * (this_type::*unspecified_bool_type)() const; > > operator unspecified_bool_type() const // never throws > { return px == 0? 0: &this_type::get; } > > Why this is better than: > > operator bool() const > { return px != 0; } > > What more can I do with somethin like this? Actually, that's used to prevent mistakes; bool is an integral type, so if you add an implicit conversion to bool, then your smart pointer class can participate in integral promotions. Which allows lots of bad code to compile. :) For an example, implicit conversion to an integral type defines all the comparision operators with any other integral-convertible class. e.g., shared_ptr<int> x; scoped_ptr<int> y; (x == y); // does not do what you might expect... For more information on the problem, see the following reference: More Effective C++, Scott Myers :: Item 28 :: Testing Smart Pointers for Nullness or search the Boost developer archives. -Steve

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shared_ptr - implicit conversion to bool
by wasekvesely <vaclav.vesely＠volny.cz> 29 Jan '03

29 Jan '03

Hi, I've found this in "shared_ptr.hpp": // implicit conversion to "bool" typedef T * (this_type::*unspecified_bool_type)() const; operator unspecified_bool_type() const // never throws { return px == 0? 0: &this_type::get; } Why this is better than: operator bool() const { return px != 0; } What more can I do with somethin like this? Thank you, Wasek

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RE: [Boost-Users] Re: Why is <boost::function>::_1 not in namespa ce boost?
by Tom Matelich 29 Jan '03

29 Jan '03

> > I think I agree with Markus that it is in fact broken. It's easy to > imagine dependency scenarios like this: > > lambda <-- libA <-\ > }--> App > bind <-- libB <-/ > > The guy writing App shouldn't have to be aware of the dependency > conflict between libA and libB. Isn't this only a problem within translation units? I suppose lambda and bind might be included in headers from libA and libB into a single translation unit in App, but seems unlikely. ----------------------------------------------------------------------- DISCLAIMER: Information contained in this message and/or attachment(s) may contain confidential information of Zetec, Inc. If you have received this transmission in error, please notify the sender by return email. -----------------------------------------------------------------------

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Advice on using iterator_adapter
by Rob Smallshire 28 Jan '03

28 Jan '03

Boosters, I have implemented a 'virtual container' class (i.e. it looks and behaves like it contains Objects, but it fact it doesn't) which implements an iterator interface of what are essentially bidirectional iterators. The iterators I have now are not STL compliant and I only have 'mutable' versions of the iterators, with no corresponding const iterators. Some guidance on how to make the best use of boost::iterator adapter would be appreciated to create fully STL compliant iterator/const_iterator pairs: 1) Out current iterators (i.e. the Base type which will be adapted) return smart reference objects when dereferenced, rather than true C++ references to objects. Will iterator adapter work in this situation? 2) Furthermore, can I use the iterator_adapter to adapt our home-grown mutable iterator into a STL compliant const_iterator? Do I simply modify the Reference of the iterator_adapter template type to be a const version of my smart-reference class? Many thanks, Rob

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Why is <boost::function>::_1 not in namespace boost?
by Markus Werle 28 Jan '03

28 Jan '03

Hi! the placeholders in boost/bin/placeholders.hpp are put in an anonymous namespace. This is awkward, since like this they are visible even in places where I do not want them to be so, e.g.: #include <all_of_boost_lambda> #include <all_of_boost_function> // not unlikely to use both [...] { using namespace boost::lambda; std::for_each(v.begin(), v.end(), std::cerr << _1 << constant(' ')); } In such cases the "_1" is ambigous, since boost::lambda::_1 and and <anonymous>::_1 are both visible. This means that code which used to include boost_lambda stuff may change its meaning (or get ambigous) just by including another boost header. Could we not place those placeholders into namespace boost, just to get rid of the ambiguity? Any caveats I overlooked? (using my own placeholder definitions and BOOST_BIND_NO_PLACEHOLDERS is not really a satisfying solution) Markus

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RE: [Boost-Users] Boost 101?
by Ferdinand Prantl 24 Jan '03

24 Jan '03

> From: Beman Dawes [mailto:bdawes@acm.org] > Sent: Thursday, January 23, 2003 02:50 > > At one time we published a header dependency chart, but as Boost grew > it became unwieldy and we no longer produce it. > > There have been past discussions on how to meet this need, and the > consensus is that usually what is required is a library (rather than > header) dependency analysis. Yes, I agree, it is almost impossible considering which files to include and which not with the current size of the boost package. It is sensible to declare explicitely library dependencies (tree) and use them. Nevertheless, I created a perl script some time ago to display header and library dependencies in my library with references to boost headers. I hacked it quickly to work with boost only; if you are interested it is at http://groups.yahoo.com/group/boost/files/hdr_depend. > This would be fairly easy to produce, using a number of Boost's own > libraries, of course:-) > > But the holdup is that it is only a medium priority task, and lately > has been pushed aside in favor of higher priority work. If > someone else wants > to take this one over, I'd be glad to hand it off. We want to do it > entirely in C++, so any Booster can maintain it. Well, currently I'm happily unpacking all boost but I like the idea; for example, for such a project I would like to use smart pointers only... I could spend some time on such a tool if anyone is interested, firstly gathering the requirements and then developing it. Ferda > > --Beman

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Problem with linking to boost::signals
by René Möhring 24 Jan '03

24 Jan '03

I try to use boost signals and have the following code from the tutorial. #include <boost/signal.hpp> #include <iostream> struct HelloWorld { void operator()() const { std::cout << "Hello, World!" << std::endl; } }; int main() { // Signal with no arguments and a void return value boost::signal<void ()> sig; // Connect a HelloWorld slot HelloWorld hello; sig.connect(hello); // Call all of the slots sig(); } This compiles but gives these errors while linking: /usr/bin/ld: warning: libstdc++.so.3, needed by /usr/local/lib//libboost_signals.so, may conflict with libstdc++.so.4 test.o: In function `_ZN5boost4slotINS_8functionIFvvENS_6detail8function8unusableES5_S5_S5_ S5_S5_S5_S5_S5_S5_EEEC1I10HelloWorldEERKT_': test.o(.gnu.linkonce.t._ZN5boost4slotINS_8functionIFvvENS_6detail8funct ion8unusableES5_S5_S5_S5_S5_S5_S5_S5_S5_EEEC1I10HelloWorldEERKT_+0xac): undefined reference to `boost::signals::detail::slot_base::create_connection()' test.o: In function `_ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIiENS_8functionIFvvENS_6 detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_S9_EEE7connectERKNS_4s lotISA_EE': test.o(.gnu.linkonce.t._ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIi ENS_8functionIFvvENS_6detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_ S9_EEE7connectERKNS_4slotISA_EE+0x83): undefined reference to `boost::signals::detail::signal_base_impl::connect_slot(boost::any const&, boost::any const&, std::vector<boost::signals::trackable const*, std::allocator<boost::signals::trackable const*> > const&)' test.o: In function `_ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIiENS_8functionIFvvENS_6 detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_S9_EEEclEv': test.o(.gnu.linkonce.t._ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIi ENS_8functionIFvvENS_6detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_ S9_EEEclEv+0x15): undefined reference to `boost::signals::detail::call_notification::call_notification(boost::sh ared_ptr<boost::signals::detail::signal_base_impl> const&)' test.o(.gnu.linkonce.t._ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIi ENS_8functionIFvvENS_6detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_ S9_EEEclEv+0x155): undefined reference to `boost::signals::detail::call_notification::~call_notification()' test.o(.gnu.linkonce.t._ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIi ENS_8functionIFvvENS_6detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_ S9_EEEclEv+0x1c7): undefined reference to `boost::signals::detail::call_notification::~call_notification()' test.o: In function `_ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIiENS_8functionIFvvENS_6 detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_S9_EEEC2ERKS2_RKS4_': test.o(.gnu.linkonce.t._ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIi ENS_8functionIFvvENS_6detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_ S9_EEEC2ERKS2_RKS4_+0xa6): undefined reference to `boost::signals::detail::signal_base::~signal_base()' test.o: In function `boost::signals::connection::~connection()': test.o(.gnu.linkonce.t._ZN5boost7signals10connectionD1Ev+0x16): undefined reference to `boost::signals::connection::disconnect() const' test.o: In function `boost::signals::detail::signal_base::signal_base(boost::function2<bool, boost::any, boost::any, boost::empty_function_policy, boost::empty_function_mixin, std::allocator<boost::function_base> > const&)': test.o(.gnu.linkonce.t._ZN5boost7signals6detail11signal_baseC2ERKNS_9fu nction2IbNS_3anyES4_NS_21empty_function_policyENS_20empty_function_mixi nESaINS_13function_baseEEEE+0x41): undefined reference to `boost::signals::detail::signal_base_impl::signal_base_impl(boost::func tion2<bool, boost::any, boost::any, boost::empty_function_policy, boost::empty_function_mixin, std::allocator<boost::function_base> > const&)' test.o: In function `_ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIiENS_8functionIFvvENS_6 detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_S9_EEED2Ev': test.o(.gnu.linkonce.t._ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIi ENS_8functionIFvvENS_6detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_ S9_EEED2Ev+0x11): undefined reference to`boost::signals::trackable::~trackable()' test.o(.gnu.linkonce.t._ZN5boost7signal0IvNS_10last_valueIvEEiSt4lessIi ENS_8functionIFvvENS_6detail8function8unusableES9_S9_S9_S9_S9_S9_S9_S9_ S9_EEED2Ev+0x1f): undefined reference to`boost::signals::detail::signal_base::~signal_base()' test.o: In function `void boost::checked_delete<boost::signals::detail::signal_base_impl>(boost:: signals::detail::signal_base_impl*)': test.o(.gnu.linkonce.t._ZN5boost14checked_deleteINS_7signals6detail16si gnal_base_implEEEvPT_+0x19): undefined reference to`boost::signals::detail::signal_base_impl::~signal_base_impl()' My compiler is gcc 3.2 on FreeBSD. g++ -o signals test.cpp -I/usr/local/include -L/usr/local/lib/ -lboost_signals Do you have an idea what I am doing wrong?

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Specifying a case-insensitive rule for a regex algorithm
by Amittai Aviram 23 Jan '03

23 Jan '03

Hi! I am using boost::regex_grep() and boost::regex_search(), and I've figured out how to set a given rule to be case-insensitive when I transform it from a string into a rule -- i.e., -- boost::regex("search[[:space:]]string", boost::regbase::normal | boost::regbase::icase) This is great. But in many regular expression processing environments, you also have the option to specify case-insensitivity (or sensitivity) within the rule string itself. For instance, in Perl, you do it with the /i switch at the end of the rule string, and in some environments you can use (?i) to make the following characters case-insensitive when processed and then (?-i) to switch case sensitivity back on. I didn't see any mention of any such thing in the regex documentation. Is this option not available in boost::regex? Thanks! Amittai Aviram amittai(a)amittai.com

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Problems using date-time library
by Keno 22 Jan '03

22 Jan '03

Greets all, I'm in need of using the Date-Time library but I'm encountering a few issues. I tried compiling the following simple code: ----------------- #include <boost/date_time/gregorian/gregorian.hpp> #include <iostream> using namespace boost::gregorian; int main() { date birthday(1979,3,26); return 0; } ------------------- and got the following error(s): --------------------Configuration: boost_date - Win32 Debug-------------------- Compiling... test_date.cpp d:\softdev\vstudio6\vc98\include\new(35) : warning C4290: C++ Exception Specification ignored Linking... test_date.obj : error LNK2001: unresolved external symbol "public: static unsigned long __cdecl boost::date_time::gregorian_calendar_base<struct boost::date_time::year_month_day_base<class boost::gregorian::greg_year,class boost::gregorian::greg_mon th,class boost::gregorian::greg_day>,unsigned long>::day_number(struct boost::date_time::year_month_day_base<class boost::gregorian::greg_year,class boost::gregorian::greg_month,class boost::gregorian::greg_day> const &)" (?day_number@?$gregorian_ca lendar_base@U?$year_month_day_base@Vgreg_year@gregorian@boost@@Vgreg_month@2 3@Vgreg_day@23@@date_time@boost@@K@date_time@boost@@SAKABU?$year_month_day_b ase@Vgreg_year@gregorian@boost@@Vgreg_month@23@Vgreg_day@23@@23@@Z) Debug/boost_date.exe : fatal error LNK1120: 1 unresolved externals Error executing link.exe. boost_date.exe - 2 error(s), 1 warning(s) ------------------------------- Any clues as to what could be happening here folks?? I'm using MSVC6 with SP5 + STLPort 4.5.3 on WinXP .: Keno :.

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random number lib: msvc6, prob compiling random_demo.cpp w mt19937
by Nick Toze <geeky_nick＠yahoo.co.uk> 15 Jan '03

15 Jan '03

Hello, I had a slight problem compiling random_demo.cpp after I had changed the typedef to: typedef boost::mt19937 base_generator_type; I got this error: --------------------Configuration: random_demo - Win32 Debug-------------------- Compiling... random_demo.cpp d:\c_plus_plus\boost_1_29_0\boost\random\mersenne_twister.hpp(104) : error C2064: term does not evaluate to a function d:\c_plus_plus\boost_1_29_0\boost\random\mersenne_twister.hpp(75) : see reference to function template instantiation 'void __thiscall boost::random::mersenne_twister<unsigned long,624,397,31,-1727483681,11,7,-1658038656,15,-272236544,18,-948 541730>::seed(const unsigned int &)' being compiled Error executing cl.exe. Creating browse info file... random_demo.exe - 1 error(s), 0 warning(s) I fixed it by adding an 'L' to the first line of main, i.e. base_generator_type generator(42Lu);

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