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weak_ptr
by Jason Winnebeck 23 Jul '03

23 Jul '03

Is there a reason why weak_ptr's cannot be compared with ==, or tested in a conditional? If I have two weak_ptr's, I thought it to be strange that I have to do: (w1.lock() == w2.lock()) And to test if a weak_ptr is the empty weak_ptr: if ( !(w1.lock()) ) which seems kind of awkward. Looking at the implementation, I see how the copy constructor is defined using lock. I understand what the comments are saying there. Perhaps there are some multithreaded issues that prevent equality testing I don't see. I would like the semantics that w1 and w2 compare to be equal whether or not the object they are pointing to are valid or not. I'm not sure if weak_ptrs become "empty" when the object they point to is destroyed (because there's no way to test for "emptyness" or "nullness" of a weak_ptr), but if they do I can see how the equality test can't work, but not the conditional test. Even so, why is there not an operator == provided that locks both weak_ptr? Is it acceptable (the documentation didn't make it clear to me), to use if ( w1.expired() ) to test if simply if w1 is "null" or "reset". What I am trying to do is have a "current" pointer that takes the value of something I want to be set (or note the fact that nothing is set), but I don't care if the object dies while that pointer is set -- in fact I don't want to keep it alive because I don't have an easy way to call reset on current were I to make it a shared_ptr. Jason

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date-time library and ispunct() ambiguity under MSVC6
by Carl Waldbieser 23 Jul '03

23 Jul '03

I get the following compilation error for this simple program under MSVC6: ************** test.cpp****************** #include <iostream> #include "boost/date_time/gregorian/gregorian.hpp" int main() { using namespace std; cout << ispunct(',') << endl; return 0; } ************************************ error: --------------------Configuration: names_test - Win32 Debug-------------------- Compiling... test.cpp c:\documents and settings\waldbcar.waldbcar\my documents\my projects\vc\test\names_test\test.cpp(8) : error C2668: 'ispunct' : ambiguous call to overloaded function Error executing cl.exe. test.obj - 1 error(s), 0 warning(s) Normally, this sort of thing would not be a problem, as I typically would just be using the qualified std::ispunct() instead of a using directive. However, this problem cropped up when I was trying to use the date-time library in conjuction with the Spirit parsing library. Spirit implements some function by doing exactly what I did in the above sample-- using a using directive and then calling ispunct() unqualified. I am guessing the ratonale behind this might have something to do with the fact that under MSVC6, functions like ispunct() (and most or all of <ccytpe>) seem to have been dumped into the global namespace by default. However, it seems like the date-time library must be doing something like: namespace std { using ::ispunct; } somewhere in its internals (or maybe just using something else that does?). Anyway, it seems to be a shame that I can't get these two great libraries to work together on my compiler. Is there any chance that someone out there might have a solution? Carl Waldbieser waldbie<at-sign>attglobal.net

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boost::date_time + setting system clock
by ericd 22 Jul '03

22 Jul '03

afternoon all, I was wondering if it is possible to set the clock using date_time. I been looking but have found no clue that it is so. From what I have seen so far, this library does a lot of cool stuff, and why not this. I am working on a little personal project that uses an ORB. The idea is to have all clocks synchronized. I have one machine that queries an atomic time server. After having done so it will call each machine and synchronize them. I am currently running a mix of Linux, Solaris, WIN NT 2000 and XP... and it freaks me out not to have them synchronized. Any help would be appreciated... Eric

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problem building boost on solaris
by jerry_karlin 22 Jul '03

22 Jul '03

gcc-Link-action libs/test/build/bin/libboost_prg_exec_monitor.so/g cc/debug/runtime-link-static/shared-linkable-true/ threading-single/libboost_prg_exec_monitor.so ld: warning: option -d appears more than once, first setting taken ld: fatal: option -dn and -z[text|textwarn|textoff] are incompatible ld: fatal: option -dn and -G are incompatible ld: fatal: Flags processing errors collect2: ld returned 1 exit status What's causing this, and how do I fix it? I can't figure my way through these jam files just yet... Sparc Solaris 2.7, gcc-2.95.3, binutils-2.14 Any help would be... helpful. Thanks!

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Defect in intrusive_ptr.hpp
by Ilya Chvetsov(work) 22 Jul '03

22 Jul '03

Hi! It seems to me, that the following string should be inserted to intrusive_ptr.hpp <string> #include <boost/config.hpp> </string> Following code can not be compiled without this string under MSVC6SP5(with STLPort) <code> # if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, <= 1200 && __SGI_STL_PORT) // MSVC6 has problems finding std::basic_ostream through the using declaration in namespace _STL using std::basic_ostream; template<class E, class T, class Y> basic_ostream<E, T> & operator<< (basic_ostream<E, T> & os, intrusive_ptr<Y> const & p) # else template<class E, class T, class Y> std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p) # endif { os << p.get(); return os; } </code> -Ilya

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shared_ptr or weak_ptr in general
by Jason Winnebeck 22 Jul '03

22 Jul '03

I just wanted to follow up on my previous thread about my issues I've been discussing on the list with a general question. By default should I try to use shared_ptr or weak_ptr? I had always thought that shared_ptr should always be used except for rare cases where weak_ptr's semantics is either very desirable or needed. Now my pointers experience so far has been limited to explicit memory management (new/delete) and in Java with its references, where any reference keeps an object alive, and weak references exist but I've never used them despite a few years of using Java on the job. Based on some of the discussion (particularly from Mr Dimov), made me think that weak_ptr may be desirable a lot more often than I previously thought. I know that shared_ptr, unlike Java, is suceptable to cycles. And I feel that shared_ptr is better and less bug prone than new/delete but I'm afraid I'll have cycle problems if I just start throwing shared_ptr all over the place. I know that in my code I have back pointers all over the place, which I thought was pretty common, but I have realized that that only occurs when I'm following the generator/listener design scheme, and I've gotten that figured out. So A to B, B to A cycles don't concern me much but I do wonder about long cycles if I use shared_ptr a lot. The rule of thumb I'm using right now is to look for cycles if I "convert" a class to use shared_ptr (static crate method) that contains shared_ptr objects, similar to the rule I use to check for deadlocks with mutexes. But with all of these rules checking for safety I begin to question somewhat the benefits of shared_ptr over normal pointers. I suppose with shared_ptr you can only leak memory whereas with normal pointers you can do lots of nasty uninitialized accesses. I can see an argument that using shared_ptr only when needed and weak_ptr otherwise can help prevent cycles. But using weak_ptr requires the code to handle both cases of the lock operation, and I'm still unsure about any performance issues with lock if there is a mutex involved -- although too slight to not choose weak_ptr, it is enough to ask why not choose shared_ptr over weak_ptr if they both work equally well. Thank you for your comments and patience with my attemps at understanding, Jason Winnebeck

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staticially linked STLport and Boost
by hh10k 20 Jul '03

20 Jul '03

I've compiled STLport for vc6, and can compile Boost with this: bjam "-sTOOLS=msvc-stlport" "-sBUILD=debug <stlport-iostream>on" So far so good, but when I try to compile a simple Boost.Python example (why I got Boost) I get a heap of link errors because Boost has linked with the DLL version of STLport, and I want it statically linked. I thought it's meant to default to static, but I can only guess that STLport is detecting otherwise. So, in order to force Boost to use the static verion, I tried: bjam "-sTOOLS=msvc-stlport" "-sBUILD=debug <stlport-iostream>on <define>_STLP_USE_STATIC_LIB" But now I get errors like: vc-Link libs\python\build\bin\boost_python.dll\msvc-stlport\debug\runtime-link-dynamic\stlport-cstd-namespace-std\stlport-iostream-on\stlport-version-4.5.3\boost_python_debug.dll libs\python\build\bin\boost_python.dll\msvc-stlport\debug\runtime-link-dynamic\stlport-cstd-namespace-std\stlport-iostream-on\stlport-version-4.5.3\boost_python_debug.lib msvcprtd.lib(MSVCP60D.dll) : error LNK2005: "public: __thiscall std::bad_alloc::bad_alloc(char const *)" (??0bad_alloc@std@@QAE@PBD@Z) already defined in stlport_vc6_stldebug_static.lib(dll_main.obj) LIBCMTD.lib(osfinfo.obj) : error LNK2005: __get_osfhandle already defined in MSVCRTD.lib(MSVCRTD.dll) LIBCMTD.lib(dbgheap.obj) : error LNK2005: _malloc already defined in MSVCRTD.lib(MSVCRTD.dll) ...lots more errors... This isn't just a problem with Boost.Python. Anything else that builds a dll or exe has the same errors. The first error seems really strange, because I can't understand how std::bad_alloc should exist in stlport_vc6_stldebug_static.lib(dll_main.obj). STLport does define it's own bad_alloc, but it also #defines std to _STL so there should be no 'std'. When I use bad_alloc in my own programs I don't have any problems, so I can only assume it's Boost. I've wasted so much time trying to work this out, but I don't know much about the Boost build process. What's going wrong?

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Unusal regex behavior.
by sdf sdf 20 Jul '03

20 Jul '03

Hellos everyone! Here is a good one. I am using regex and am having some weird returns. I can assign my results to a std:vector <std:string>. The vector[0] does contain the correct match, but vector[1] does not contain what is in a set of parentheses as it should. In fact I usually get a segment fault when I try to access it. I then found I can access results from the grep by using the boost::Regex.What(n). However What(0) returns the next available match in the string, and What(1) and up will correctly report the substrings defined in this second match correctly. If no second match is available then the What() member will return the original match. How do I fix the vector problem? OR? Does using What() force another search to take place? And if so can I change that behavior? Code snippet: string reg_string ="[0-9]{3}(-[0-9]{2}-)[0-9]{4}"; //yes it is a SSN string search_string = "Big Bird \n123 sesame street \n the bronx NY 11722\n545-65-2343\nmorestuff\nandevenmore\nSnuff E Lufigous \n 234 sesame street \n the bronx NY 11722\n889-99-5527\nmorestuff\nandevenmore\n"; std::vector<std::string> results; boost::regex regsearch = boost::regex(reg_string,false); int num_matchs; num_matchs=regsearch.Grep(results, search_string, boost::match_any); cout << num_matchs << " Number of Matchs\n"; // this is 2 cout << results[0] << " results return string vector[0] \n"; // this is 545-65-2343 cout << regsearch.What(0) << " results from what(0) \n"; // this is 889-99-5527 cout << regsearch.What(1) << "results from what(1) \n";// this is -99- //this line aborts // cout << results[1] << " results return string vector[1] \n"; // this should be -65- HELP. Note I never ran the code above, but I think it is correct. __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com

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filesystem help
by Christian Gmeiner 20 Jul '03

20 Jul '03

Hello! This is my problem: I have an std::string contains something like C:\Test\Media\Cloud.dds. Now i want to extract the Cloud.dds. This is, what i have tried: fs::path temp(Name, fs::native); fs::directory_iterator dir_itr(temp); Name = dir_itr->leaf(); Where is my error? This code throughs an exception. Thanks, Christian Gmeiner

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Multiple inheritance and enable_shared_from_this
by Jason Winnebeck 20 Jul '03

20 Jul '03

Can you multiply inherit from objects that inherit from enable_shared_from_this? It seems not. My program compiled on MSVC.NET "crashes" due to shared_from_this throwing boost::bad_weak_ptr. Originally when I started using shared_ptr I wanted to have an ability to obtain a shared_ptr to this since my objects sometimes register themselves. The way I do it now is like this: static sptr create() { sptr ret( new Object() ); ret->setThisPtr( ret ); return ret; } However it is very easy to forget which classes you inherit from that force you to call setThisPtr. A good use of the assert statement helps but I'd rather not do this. The problem is that I use multiple inheritance in one place: static sptr create() { sptr ret( new ComplexObject() ); ret->BaseA::setThisPtr( ret ); ret->BaseB::setThisPtr( ret ); return ret; } I thought I'd use enable_shared_from_this but as I said it crashes. The following program as tested on MSVC.NET throws boost::bad_weak_ptr then the line "Base2::sptr b2 = c->Base2::getThis();" is executed. #include <iostream> #include <boost/smart_ptr.hpp> #include <boost/enable_shared_from_this.hpp> using namespace std; template <class T> class SharedThis : public boost::enable_shared_from_this<T> { public: boost::shared_ptr<T> getThis() { return shared_from_this(); } }; class Base1 : public SharedThis<Base1> { public: typedef boost::shared_ptr<Base1> sptr; typedef boost::weak_ptr<Base1> wptr; protected: Base1() { cout << "Base1 ctor" << endl; } public: virtual ~Base1() { cout << "Base1 dtor" << endl; } static sptr create() { return sptr( new Base1() ); } private: Base1( const Base1& o ); Base1& operator = ( const Base1& rhs ); }; //Base2 is identical to Base1 except different name class Base2 : public SharedThis<Base2> { public: typedef boost::shared_ptr<Base2> sptr; typedef boost::weak_ptr<Base2> wptr; protected: Base2() { cout << "Base2 ctor" << endl; } public: virtual ~Base2() { cout << "Base2 dtor" << endl; } static sptr create() { return sptr( new Base2() ); } private: Base2( const Base2& o ); Base2& operator = ( const Base2& rhs ); }; class Child : public Base1, public Base2 { public: typedef boost::shared_ptr<Child> sptr; typedef boost::weak_ptr<Child> wptr; protected: Child() { cout << "Child ctor" << endl; } public: virtual ~Child() { cout << "Child dtor" << endl; } static sptr create() { return sptr( new Child() ); } }; int main( int argc, char* argv[] ) { Child::sptr c = Child::create(); Base1::sptr b1 = c->Base1::getThis(); Base2::sptr b2 = c->Base2::getThis(); /* assert( c.get() == c->Base1::getThis().get() ); assert( c.get() == c->Base2::getThis().get() ); assert( c == c->Base1::getThis() ); assert( c == c->Base2::getThis() ); */ }

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