October 2005 - Boost-users - lists.boost.org

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

2 1

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.

2 1

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?

2 1

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

3 4

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.

2 1

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

2 1

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

1 0

File system - File creation time
by Vance T Thornton 05 Oct '05

05 Oct '05

Does a Boost file system method exist to retrieve / set the creation time of a file?

1 0

Boost.python- MinGW install on XP
by Francesco A. Queirolo 05 Oct '05

05 Oct '05

Hello all I am trying to install (only) boost.python on my XP box to a directory other than the default C:Boost. I am running all of the command line options from a DOS command prompt. Boost: 1.33.0 Python: 2.4.2 (Final) MinGw: 4.1.1 I try: D:\Dev\boost_1_33_0\libs\python\build>bjam "--prefix=D:\Dev\boosttarget" "-sTOOLS=mingw" "--with-python-root=D:\Dev\Python24" "--with-python" install from a DOS command prompt. Where: D:\Dev\boosttarget is an existing directory mingw\bin is in my System path D:\Dev\Python24 is my python root My pexports output: Python24.a is in C:\WINDOWS\system32 The bjam output is: --------------------------------------------------------------------- *** If you don't need Boost.Python, you can ignore this section *** *** pass --without-python to suppress this message in the future *** skipping Boost.Python library build due to missing or incorrect configuration couldn't find Python.h in "c:/tools/python/include" You can configure the location of your python installation by setting: PYTHON_ROOT - currently "c:/tools/python" PYTHON_VERSION - The 2-part python Major.Minor version number (e.g. "2.2", NOT "2.2.1") - currently "2.2" The following are automatically configured from PYTHON_ROOT if not otherwise set: PYTHON_LIB_PATH - path to Python library object; currently "c:/tools/python/libs" --------------------------------------------------------------------- don't know how to make install ...found 1 target... ...can't find 1 target... I can give you any other system or set up parameters. BTW I specified where my python root is so I have no idea why it can't find Python.h! Thank you very much, Francesco

2 1

[Threads]
by lukas 05 Oct '05

05 Oct '05

hi I'm new to boost.threads and have a basic question. During program execution the user has to check the connection to a server. This action should take place in a simple thread. If the user gets bored waiting for responce, he should be able to stop the process and return back to the main application. Is there a proper standard solution? For now I try to yield the thread holding the connection methods. In this case the inner methods all terminate and are not going to be stopped. My first attemp is to stop this inner methods by hand. Is there a better way to do this? kind regards, luke

4 3