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"Correct" way to return empty shared_ptr?
by dick.bridges＠tais.com 24 Apr '03

24 Apr '03

What is the 'correct' way to return a NULL/empty shared_ptr? For example, this works <snippet> shared_ptr<int> maybe_get_a_pointer() { shared_ptr<int> p; return(p); } </snippet> but seems 'klunky'. I've clearly missed something in the docs/examples somewhere. Can someone point me in the right direction? TIA

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RE: [Boost-Users] Re: pool_allocator problems on VC7.1 (real release)
by Ben Hutchings 23 Apr '03

23 Apr '03

John Harris <john.harris(a)tradingtechnologies.com> wrote: > Ben Hutchings wrote: > > I compiled almost the exact same code: > > > > #include <boost/pool/pool_alloc.hpp> > > #include <map> > > #include <utility> > > > > typedef std::basic_string<char, std::char_traits<char>, > > boost::pool_allocator<char> > t; > > > > int main() > > { > > std::map<t, t, std::less<t>, > > boost::pool_allocator<std::pair<const t, t> > > m; > > } > > > > with VC++ 7.0 and Boost 1.29, and got no warnings or errors at all. > > > > Ah, yes, that works for me, too (no warning, either), but try adding > a line of code that actually uses the map, like this: > > m["abc"] = "def"; > > and you get the following cascade of errors: <snip> Which all indicates that operator< is not defined for t, because we didn't include <string>. Let's not be so quick to blame the compiler. VC++ 7 is a long way ahead of version 6.

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Sorting list < shared_ptr < foo > > using std::list::sort()
by heath_r_davis 23 Apr '03

23 Apr '03

I have experienced some difficulty with sorting lists of type: list < shared_ptr < foo > > Here is the expected (sorted) program output: 424238335 596516649 719885386 846930886 1189641421 1649760492 1681692777 1714636915 1804289383 1957747793 Instead, I end up with: 1804289383 846930886 1681692777 1714636915 1957747793 424238335 719885386 1649760492 596516649 1189641421 Below is the code in question: //////////////////////////////////////////////// #include <iostream> #include <list> using namespace std; #include <boost/shared_ptr.hpp> using namespace boost; //////////////////////////////////////////////// class my_class { public: int m_val; public: my_class(); bool operator<(const my_class&); void Display(); }; //////////////////////////////////////////////// my_class::my_class() { m_val = rand(); } bool my_class::operator<(const my_class& arg) { return m_val < arg.m_val; } void my_class::Display() { cout << m_val << "\n"; } //////////////////////////////////////////////// int main( int argc, char **argv ) { // list < my_class > my_list; // list < my_class >::iterator my_iter; list < shared_ptr < my_class > > my_list; list < shared_ptr < my_class > >::iterator my_iter; //populate my_list for (int x=0; x<10; x++) { // my_class tmp_obj; shared_ptr < my_class > tmp_obj; tmp_obj.reset(new my_class); my_list.push_back(tmp_obj); } //sort the list my_list.sort(); //display contents of my_list my_iter = my_list.begin(); while (my_iter != my_list.end()) { // (*my_iter).Display(); (*my_iter)->Display(); ++my_iter; } return 0; } //////////////////////////////////////////////// Thanks in advance for any help you may render...

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RE: [Boost-Users] Problems linking with Boost 1.29.0 thread lib, Linux/g++ 3.2.2 -r2
by Ben Hutchings 23 Apr '03

23 Apr '03

subsample <knuarv(a)nith.no> wrote: > Failing to link a program with libboost_thread, even though I supply > the -lboost_thread directive in the makefile. I'm kind of new to > makefiles, having only used Visual C++ in Windows untill recently. I > 've tried changing things around a bit, doesn't help. A minimal test > program I wrote links fine with boost_thread though. My makefile looks > like this: > CC=g++ > CFLAGS=-g > LDFLAGS=-L/home/sub/Libs/alsa/lib -lasound -lboost_thread -lpthread > > alsatest: alsatest.o > $(CC) $(LDFLAGS) -o alsatest SmallObj.o alsatest.o <snip> ld doesn't work this way. -l is just a shortcut for finding a library file. The libraries specified with -l are part of the file list, same as the object files and any library files specified by their full file name. The nasty thing is that backwards references are only resolved in object files, not in library files, so library files must be listed after the object files (and any other library files) that reference them. You need to take the libraries from LDFLAGS (perhaps into another variable) and put them at the end of the command line. Also you should be using CXX and CXXFLAGS for compiling C++ code, not CC and CFLAGS. Since you're building a pthreads program, you *must* define the macro _REENTRANT to get a threadsafe C library. As a shortcut, include -pthread in CXXFLAGS (this causes linking with -lpthread, too).

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RE: [Boost-Users] pool_allocator problems on VC7.1 (real release)
by Ben Hutchings 23 Apr '03

23 Apr '03

John Harris <john.harris(a)tradingtechnologies.com> wrote: > scleary(a)jerviswebb.com wrote: > > John - > > > > Sorry, Boost.Pool does not currently support MSVC, due to that compiler's > > extreme lack of template support. > > > > I also tried this on the real released VC7.1 (which has been on MSDN > subscriber downloads for a couple of weeks, now), and, while it > compiles, I get warnings that point me to some code that looks like > it's losing precision (size_type reduced to bool) in a calculation. VC++ has produced that warning for a while now, and it's totally bogus. Notice that it's a "performance warning" not an "are you sure this is that you want?" warning, and it's being generated here for *casts* not implicit conversions. <snip> > Another test I tried was a map<string,string>, actually declared like > this: > > typedef > std::basic_string<char,std::char_traits<char>,boost::pool_allocator<ch > ar> > t; > std::map<t, t, std::less<t>, boost::pool_allocator<std::pair<const t, > t> > > m; > > ...and got these errors: <snip> I compiled almost the exact same code: #include <boost/pool/pool_alloc.hpp> #include <map> #include <utility> typedef std::basic_string<char,std::char_traits<char>,boost::pool_allocator<char > > t; int main() { std::map<t, t, std::less<t>, boost::pool_allocator<std::pair<const t, t> > > m; } with VC++ 7.0 and Boost 1.29, and got no warnings or errors at all. The command line was: cl /D__WIN32__ /EHsc /I"c:\program files\boost" test.cpp I repeated this with Boost 1.30 and again got no warnings or errors. I don't have VC++ 7.1 to hand, but I would be surprised if it broke anything that worked in 7.0.

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Signal/Slot copy semantics.
by Jesper Bojesen 23 Apr '03

23 Apr '03

I have a problem with the sematics of the the signal connect method. Consider this simple program: #include <iostream> #include <boost/signal.hpp> struct HelloWorld { void operator()() const { std::cout << "Hello, World!, the parallel world exist at " << (void *) this << std::endl; } }; int main () { // Connect a HelloWorld slot HelloWorld hello; std::cout << "Main world at " << (void *) &hello << std::endl; boost::signal<void ()> sig; sig.connect(hello); sig (); std::cout << "Thats all folks!\n"; return 0; } It produces this output: >Main world at 0xbffff2e0 >Hello, World!, the parallel world exist at 0x8056128 >Thats all folks! My problem is that the object signalled is not the same object that I subscribed to the signal. Is this really what was inteded ? Is the any rationale behind this behaviour ? -- Jesper Bojesen Medical Insight Email: jbb(a)medical-insight.com Phone mobile: (+45) 40 99 55 03 Phone direct: (+45) 46 55 04 42 Fax: (+45) 46 55 11 66

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UBLAS and algorithms
by David Johnson 23 Apr '03

23 Apr '03

Hi, I'm looking to solve some matrix problems using conjugate gradient methods. CGS and GMRES to name a couple. I see where the matricies can be stored by the UBLAS classes, but I don't see any of the algorithms available in boost. Are they available somewhere? I've looked at packages like IML++ and see them there, but they appear to use different storage classes. Can anyone point me in the direction of where some boost compatible algorithms are? Thanks, Dave

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RE: pool_allocator problems on VC7.1 (real release)
by scleary＠jerviswebb.com 23 Apr '03

23 Apr '03

> -----Original Message----- > From: John Harris [mailto:john.harris@tradingtechnologies.com] > I also tried this on the real released VC7.1 (which has been on MSDN > subscriber downloads for a couple of weeks, now), and, while it > compiles, I get warnings that point me to some code that looks like > it's losing precision (size_type reduced to bool) in a calculation. > The pool code about which the following warnings complain: > > const size_type num_chunks = total_req_size / partition_size + > static_cast<bool>(total_req_size % partition_size); > The cast is intentional. The intent is to add one if the result of the modulus is non-zero. I don't know why the compiler is producing warnings, since I'm using an explicit cast. > Another test I tried was a map<string,string>, actually declared like > this: I'm having a hard time deciphering the compiler errors (I'm not used to MSVC errors), but it looks like it might be a problem in the STL. Have you tried this with STLPort? > If you have an example of a map<string,string> using pool_allocator > that compiles on VC7.1, I'd *love* to see it. That's all I'm really > after, here. Is MSVC available for download for non-MSDN subscribers? If so, I can download it and try to get it working. -Steve

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Trouble grokking iterator adaptors
by Kris Braun 23 Apr '03

23 Apr '03

Hi there, I could really use the features provided by iterator adaptors part of the library, but I'm having a lot of trouble getting a nested set of adaptors to compile. In one case, I'd like to return an iterator into std::map< std::string, boost::shared_ptr< ApiOption > >, and have it return references to options in which option->isTemplate( ) is false. Conceptually, I'd like a filter_iterator->indirect_iterator- >projection_iterator chain. I've been using this typedef to project onto the second member of the pair: typedef boost::projection_iterator_pair_generator< select_second< std::string, boost::shared_ptr< ApiOption > >, OptionMap::iterator, OptionMap::const_iterator > OptionMapIterators; but I've been at a loss to add indirect_iterator and filter_iterator into the mix. Can anyone help me get unstuck? Thank you in advance, Kris

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RE: [Boost-Users] simplest pool_alloc example does not work on VC 6
by scleary＠jerviswebb.com 23 Apr '03

23 Apr '03

John - Sorry, Boost.Pool does not currently support MSVC, due to that compiler's extreme lack of template support. -Steve > -----Original Message----- > From: John Harris [mailto:john.harris@tradingtechnologies.com] > > Using Boost 1.30.0. MSVC6 > Tow problems: (1) I have to #define __WIN32__, and (2) Doesn't compile

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