- Boost-users - lists.boost.org

Re: [Boost-users] ld warnings when building boost on Fedora Core 4 with gcc 3.4.4
by Foster, Gareth 08 Oct '05

08 Oct '05

> So what compiler does work with boost on Fedora Core 4? Just the gcc 4.0 series? Have you investigated the gcc-compat packages? I know that if you want to install the binary version of realplayer from real.com, you have to install these *-compat packages. It may be the case that these packages cover development as well as just the running of old binaries. Worth a look to see what is there at any rate. Gaz

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Re: [Boost-users] aligned_storage / alignment_of / type_with_alignment
by Gottlob Frege 07 Oct '05

07 Oct '05

> > Date: Fri, 07 Oct 2005 08:32:34 +0200 > From: Joaqu?n M? L?pez Mu?oz <joaquin(a)tid.es> > Subject: Re: [Boost-users] aligned_storage / alignment_of / > type_with_alignment > To: boost-users(a)lists.boost.org > Message-ID: <43461682.7A1C50F0(a)tid.es> > Content-Type: text/plain; charset=iso-8859-1 > > Gottlob Frege ha escrito: > > This is *almost* correct. There's a typo in 1.33 Boost.TypeTraits docs > (corrected > in 1.33.1) by which the explanations on type_with_alignment and > aligned_storage > are swapped. So, what you want is > > template <typename T> > struct uninitted > { > aligned_storage<sizeof(T), alignment_of<T>::value>::type myT; > > void init_later(some_params) > { > new (&myT) T(some_params); > } > }; > > Apart from this, your construct is OK and works as you expect. Actually, > this is > what aligned_storage is meant to be used for. Best, > > Joaqu?n M L?pez Mu?oz > Telef?nica, Investigaci?n y Desarrollo > > OK, thanks. By its name, I thought aligned_storage sounded like the right thing (and thus I included it in the subject line) but I wasn't sure how it fit in. I think aligned_storage<sizeof(T), alignment_of<T>::value>::type deserves its own template - maybe 'storage_for' ? Anyhow, I think I have everything I need, so away I go.... Tony

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[mpl] trouble with conditionals
by Geoffrey Romer 07 Oct '05

07 Oct '05

I'm struggling with a problem of how to correctly use conditionals in MPL. In a nutshell, the problem is that the compiler greedily evaluates all parts of a conditional, even the branch that isn't followed. This is a problem not just for performance, but because sometimes the unused branch might not compile. I know that eval_if is supposed to address this problem, but unless I'm missing something, it doesn't seem to be a complete solution. It delays evaluating the branches until one of them is selected, but the compiler still evaluates the *arguments* to both branches. If the arguments themselves don't compile, I'm screwed, despite the fact that the parts of my code that are actually relevant (the branches that get used) are perfectly correct. How do I resolve this problem? Here's a toy example, a metafunction which, given a map, finds the value associated with the key "char" and, if it exists, increments the associated value (which we assume is numeric): template <typename m_map> class toy_metafunction { typedef typename if_<typename has_key<m_map, char>::type, typename insert<m_map, pair<char, typename plus<int_<1>, at<m_map, char> >::type > >::type, m_map >::type type; }; typedef typename toy_metafunction<map< > >::type result; This does not compile, because the compiler attempts to evaluate plus<int_<1>, void_>. Notice that replacing if_ with eval_if does not help, because it's not the evaluation of insert that's the problem. Thanks in advance for any help.

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aligned_storage / alignment_of / type_with_alignment
by Gottlob Frege 07 Oct '05

07 Oct '05

If for some crazy reason I want/need a uninitialized type T, how do I use type_with_alignment, etc to make it work? eg something vaguely like this: template <typename T> struct uninitted { type_with_alignment<sizeof(T), alignment_of<T>::value_type>::type myT; void init_later(some_params) { new (&myT) T(some_params); } }; Does the in-place new work? Is the unitted<T> 'just like' T in terms of memory, usage within a struct, etc? struct Foo1 { Bar bar; SomeT t; Foo foo; }; struct Foo2 { Bar bar; uninitted<SomeT> t; Foo foo; }; sizeof(Foo1) == sizeof(Foo2) offsetof(Foo1, t) == offsetof(Foo2, t) offsetof(Foo1, foo) == offsetof(Foo2, foo) all true? Thanks Tony

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Re: [Boost-users] [bind] Member fn has defeated me
by BRIDGES Dick 06 Oct '05

06 Oct '05

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Simon Buchan > Sent: Wednesday, October 05, 2005 9:49 PM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] [bind] Member fn has defeated me > > > BRIDGES Dick wrote: > <snip> > > <snip> > You find it mysterious because it's not even slightly common > outside of > functional languages. (I hope Boost can change this). > Basicly: bind is > a function that creates a function (sortof) from a function and > arguments. Confused? Don't worry, that's normal. Essentially: > > bind(&X::f, &x, _1); > > is the same as: > > f_result_type bound_f(f_arg1_type arg1) > { return x.f(arg1); > } > > // ... > > &bound_f > > but with less hassles (ie. x can be local) If I could start with a "bound" x, I probably wouldn't have so much trouble with the concept. I get confused when trying to deal with the implied 'this' when starting from the bind(&X::f, _1, _2) form. In the current case [i.e., void f(bool)], I think _2 represents the bool parameter and can't figure out how to express the unbound 'this'. Clearly there is an error in my understanding of the underlying concept.

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Re: [Boost-users] Problem with shared_ptr and pthreads_mutex_lock
by Sohail Somani 06 Oct '05

06 Oct '05

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Kurt Kohler > Sent: Thursday, October 06, 2005 10:53 AM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] Problem with shared_ptr and > pthreads_mutex_lock > > > I've verified to my own satisfaction that the gcc and boost > versions are > *not* the same, since the boost version doesn't have the bug > I was seeing. > > I'm not exactly sure where to report stdc++ library bugs, but > I subscribed to the mailing list so I assume I'll find out. Kinda makes you wonder why they wouldn't just copy the boost implementation. But then I guess theres legal issues with that?

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Problem with shared_ptr and pthreads_mutex_lock
by Kurt Kohler 06 Oct '05

06 Oct '05

I've run into a strange problem using shared_ptr which I've reduced to the following simple case. #include <tr1/memory> class X { public: typedef std::tr1::shared_ptr<X> Ptr; int x; }; int main(int argc, char *argv[]) { for (int i = 0; i < 100; i++) { X::Ptr pX(new X); } return EXIT_SUCCESS; } Compiling with g++ 4.0.1 on a Debian system with "-O0 -g -fno-inline -DDEBUG". When this program is run under Valgrind (MemCheck) repeated messages like the following occur. ==9950== Conditional jump or move depends on uninitialized value(s) ==9950== at 0x1BBB6D9A: pthread_mutex_lock (in /lib/tls/libpthread-2.3.5.so) ==9950== by 0x1BB56C75: pthread_mutex_lock (in /lib/tls/libc-2.3.5.so) ==9950== by 0x804BF29: __gthread_mutex_lock(pthread_mutex_t*) (gthr-default.h:510) ==9950== by 0x8057ACD: std::tr1::_Sp_counted_base::release() (boost_shared_ptr.h:148) ==9950== by 0x8057B14: std::tr1::shared_count::~shared_count() (boost_shared_ptr.h:266) ==9950== by 0x806B1F4: std::tr1::shared_ptr<X>::~shared_ptr() (boost_shared_ptr.h:474) ==9950== by 0x806B1C9: main (main.cpp:30) ==9950== In the real code this leads to either a hang or an assert in pthread_mutex_lock. If the created pointer is put in a container then this doesn't seem to happen although the problem may just be postponed (the program is never able to complete). I've tried Electric Fence and dmalloc but neither told me anything useful. The hang or assert occurs at the same point every time unless the program is changed or the environment changes (e.g., running under Valgrind). It seems consistent with uninitialized memory. But why? And more important, what can I do about it? Any help would be greatly appreciated! Kurt Kohler Alpha Omega Computer Systems Corvallis, OR

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Tokenizer: BCB AnsiString and std:string
by CN 06 Oct '05

06 Oct '05

Hi! The following version incorrectly produces the result: < > 1 //---------------------- #include<iostream> #include<boost/tokenizer.hpp> #include <vcl.h> #pragma hdrstop #pragma argsused int main(int argc, char* argv[]) { using namespace std; using namespace boost; AnsiString As = "*"; typedef tokenizer<boost::char_separator<char> > Tok; char_separator<char> sep(", "); Tok tokens(string(As.c_str(),As.Length()), sep); for(Tok::iterator tok_iter = tokens.begin();tok_iter != tokens.end(); ++tok_iter) cout << "<" << *tok_iter << "> " << (*tok_iter).size(); return EXIT_SUCCESS; } //---------------------- However, this version correctly outputs this result: <*> 1 #include<iostream> #include<boost/tokenizer.hpp> #include <vcl.h> #pragma hdrstop #pragma argsused int main(int argc, char* argv[]) { using namespace std; using namespace boost; AnsiString As = "*"; string str=string(As.c_str(),As.Length()); typedef tokenizer<boost::char_separator<char> > Tok; char_separator<char> sep(", "); Tok tokens(str, sep); for(Tok::iterator tok_iter = tokens.begin();tok_iter != tokens.end(); ++tok_iter) cout << "<" << *tok_iter << "> " << (*tok_iter).size(); return EXIT_SUCCESS; } //---------------------- Why the firt version mulfunctions? TIA and Regards, CN -- http://www.fastmail.fm - A fast, anti-spam email service.

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Re: [Boost-users] [bind] Member fn has defeated me
by BRIDGES Dick 06 Oct '05

06 Oct '05

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Peter Dimov > Sent: Wednesday, October 05, 2005 10:41 AM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] [bind] Member fn has defeated me > > > BRIDGES Dick wrote: > > >> BRIDGES Dick wrote: > >> > >>> class Bar { > >>> typedef void (*pf)(bool); > >> > >> If you make this > >> > >> typedef boost::function<void(bool)> pf; > >> > > [snip] > >> > >> then > >> > >> Bar bar_( boost::bind(&X::f, &x) ); > >> > >> should work. But you can't get an oridnary function pointer from > >> boost::bind; a function pointer doesn't have enough state to > >> represent &X::f + &x. > > > > <error_message> > > [...] > > I omitted too much of the context, sorry ;-) For > > struct X > > { > void f(bool b) {} > } > > > the correct thing would be to use boost::bind(&X::f, &x, _1) > so that the > bool argument from pf (the first input argument is _1 in bind > notation) can > be passed to X::f. Works fine now. I don't know why I find boost::bind so mysterious, but I *WILL* learn! Thank you for both the answers and your patience. Regards, Dick

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boost & scons - no such file
by Imran Akbar 05 Oct '05

05 Oct '05

Hi, Using boost & scons for a program, and have it setup correctly: downloaded http://prdownloads.sourceforge.net/boost/boost_1_33_0.exe?download http://prdownloads.sourceforge.net/boost/boost-jam-3.1.11-1-ntx86.zip?downl… bjam "-sTOOLS=vc-7_1" --with-python-root="c:\python2" install and corrected the python version installed succesfully to C:\Boost getting the error: cannot open include file 'boost/function.hpp' no such file or directory Any ideas? How do you search the mailing list archive? Thanks, Imran

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