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lambda BLL question
by Neal D. Becker 10 Mar '04

10 Mar '04

I was just trying out lambda and I have a question. I have a template class Ave template<typename in_t, typename Scale> struct Ave {...} It takes a function type argument "Scale". Here's a test: typedef typeof (_1 * 0.1) some_type; some_type func (_1 * 0.1); // Ave<double, typeof (_1 * 0.1)> ave (_1 * 0.1); << this will work Ave<double, some_type> ave (func); << this will also What is the preferred way to do this without "typeof"? How do I get the type returned by the lambda expression to feed to the template Ave?

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[filesystem] create_directories not thread-safe?
by Vladimir Prus 10 Mar '04

10 Mar '04

I have an application which sometimes fails saying that it can't create a directory, because it already exists. The directory is created by fs::create_directories("run"); and the application is multi-threaded. It seems there's a race condition: if (ph.empty() || exists(ph)) return; // First create branch, by calling ourself recursively create_directories(ph.branch_path()); // Now that parent's path exists, create the directory create_directory(ph); After one thread checks that 'ph' does not exist, another one creates the same directory, so call to 'create_directory' fails. What can be done? Basically, adding a mutex for MT build and adding a warning to docs are the variants. Opinions? - Volodya

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Re:[boost] Re: [serialization17] demo_fast_binary_archive.cpp CANNOT compile in gcc 3.3.3
by Robert Ramey 10 Mar '04

10 Mar '04

David Abrahams wrote: >"Allen Yao" <yaozhen(a)ustc.edu> writes: >> It seems that gcc does not allow this kind of template argument deduction: >> >> template <int N> >> void f(int a[N]) >> { >> for (int i = 0; i < N; i++) >> cout << a[i] << " "; >> cout << endl; >> } >> >> int main() >> { >> int a[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; >> >> f(a); >> } >> >> The error message is: >> >> error: no matching function for call to `f(int[10])' > >> I would like to know how to fix this. Is there any workaround? >> Or if I am missing something? >You're missing something. Your declaration of f is equivalent to: > template <int N> > void f(int* a); >try: > template <int N> > void f(int a(&)[N]) ^^^ >instead. Hmm - that didn't work for me. But with the above hint I made the following compile and function with both VC 7.1 and gcc. template <int N> void f(int (& a)[N]) ^^^^ I had never been able to get demo_fast_binary_archive but could never figure out the reason - Mystery Solved ! Robert Ramey

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another compilation problem
by Pavol Droba 10 Mar '04

10 Mar '04

Hi, I have another compilation problem, that I could use some help with. When I try to compile libs/algorithm/string/test/replace_test.cpp with gcc3.3.1 in release mode, it fails on out-of-memory error after allocating more then 400MB of memory. Older version of compiler were able to compile it, but it took something like an hour on 1Ghz Pentium III machine (As comparison, it takes just 2 minutes with vc7.1). I thought that it is just a bug in gcc optimization, but now it seems, that intel 8.0 has also similar problems. http://tinyurl.com/vbrx#algorithm/string-replace-intel-8.0-linux Have somebody encountered the similar problem? Thanks for help, Pavol

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AIX vacpp question
by Pavol Droba 10 Mar '04

10 Mar '04

Hi, VACPP compiler is failing one of the test cases of the string_algo library. http://boost.sourceforge.net/regression-logs/cs-AIX-links.html#algorithm-re… It is the check for sequence traits. It seem, that trait classes did not get instantiated. Is there something special that this compiler needs, to avoid this problem? Other compilers do not seem to have a problem. It is not possible to instantiate all trait explicitly, because the template paramteres are mostly template again. I might have forgotten something, that other compilers just ignore. Can anybody give me some hints? Thanks, Pavol.

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RE: [boost] Re: On bind::operator==, again
by Powell, Gary 10 Mar '04

10 Mar '04

> but my recent >attempts to use Lambda have been a dismal failure, mostly because of >subtle (and sometimes not-so-subtle) differences with Bind. For >example, Lambda doesn't seem to support get_pointer to dereference >through smart pointers. Yeah, in the past I've had to bind the operator->() to the smart pointer argument and that looks plain ugly! Plus its not good for generic programming, you end up having to do some template magic to get it to call the right version, (native pointer * -> vs smart_ptr::operator->() ) >I'm rather discouraged with how difficult it is to use standard >algorithms -- or even algorithms over sequences as opposed to >iterators -- to write something that could be coded quickly using dumb >loops. Yep, me too. That's why we wrote lambda in the first place. And that's why I'm promoting decltype and auto, and varidac templates, and why its imperative we figure out how to do anonymous functions. >I hold out some hope that the long-promised integration of >Lambda and Phoenix will help to solve these problems, but it's hard >to tell when (or if) that's actually coming. That's the trouble with day jobs and mortgages vs free coding. Just not enough time in the day to do everything. >Glum in Somerville, >Dave Don't be glum soon you will be in Sunny Australia! Yours, -Gary-

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Re: [serialization17] demo_fast_binary_archive.cpp CANNOT compile in gcc 3.3.3
by Krishna Achuthan (TT) 10 Mar '04

10 Mar '04

David Abrahams wrote: >"Allen Yao" <yaozhen(a)ustc.edu> writes: > > > It seems that gcc does not allow this kind of template argument deduction: > > > > template <int N> > > void f(int a[N]) > > { > > for (int i = 0; i < N; i++) > > cout << a[i] << " "; > > cout << endl; > > } > > > > int main() > > { > > int a[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; > > > > f(a); > > } > > > > The error message is: > > > > error: no matching function for call to `f(int[10])' > > > > I would like to know how to fix this. Is there any workaround? > > Or if I am missing something? > > You're missing something. Your declaration of f is equivalent to: > > template <int N> > void f(int* a); > > try: > > template <int N> > void f(int a(&)[N]) > ^^^ > instead. > I tried both the original problem and the proposed solution on VC 7.1 For the original problem I got the following error messages: c:\Krishna\Console\Console7.cpp(242) : error C2784: 'void f(int [N])' : could not deduce template argument for 'int [N]' from 'int [10]' c:\Krishna\Console\Console7.cpp(207) : see declaration of 'f' And when I tried the proposed solution, I got the following error messages: c:\Krishna\Console\Console7.cpp(209) : error C2988: unrecognizable template declaration/definition c:\Krishna\Console\Console7.cpp(209) : error C2059: syntax error : '&' c:\Krishna\Console\Console7.cpp(209) : error C2090: function returns array c:\Krishna\Console\Console7.cpp(241) : error C2783: 'void f(int *(__cdecl *)(void))' : could not deduce template argument for 'N' c:\Krishna\Console\Console7.cpp(209) : see declaration of 'f' I did manage to find a work-around, which goes like this: template<class T> struct F; template<class T, int N> struct F<T[N]> { void operator()(T a[N]) { for (int i = 0; i < N; i++) cout << a[i] << " "; cout << endl; } }; template<class T> void f(T& a) { F<T>()(a); } int main() { int a[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; f(a); } Does it help? - Krishna Achuthan

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Implementing WaitForMultipleObjects using boost
by M Shetty 10 Mar '04

10 Mar '04

Hi, Is it possible to simulate a behaviour like WaitForMultipleObjects using boost? If yes, kindly let me know. Thanks and Regards, M Shetty ___________________________________________________ Check-out GO.com GO get your free GO E-Mail account with expanded storage of 6 MB! http://mail.go.com

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RE: Re: [boost] Implementing WaitForMultipleObjects using boost
by David Turner 10 Mar '04

10 Mar '04

Hi > I was checking out if I could use Boost to port code written > for Windows to Unix. > > The code has calls to WaitForMultipleObject which I would > need to replace. You can always do the same thing by means of conditions and signals. The paradigm is slightly different, though. //... boost::condition cond; object1.signal.connect(boost::bind(&boost::condition::notify_all, &cond)); object2.signal.connect(boost::bind(&boost::condition::notify_all, &cond)); cond.wait(mutex_lock); //... In this case, the objects have explicit signals (consider the parallel to windows kernel objects, which have an implicit "signal", i.e. their wait state). Regards David Turner

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[serialization17] demo_fast_binary_archive.cpp CANNOT compile in gcc 3.3.3
by Allen Yao 10 Mar '04

10 Mar '04

It seems that gcc does not allow this kind of template argument deduction: template <int N> void f(int a[N]) { for (int i = 0; i < N; i++) cout << a[i] << " "; cout << endl; } int main() { int a[10] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; f(a); } The error message is: error: no matching function for call to `f(int[10])' I would like to know how to fix this. Is there any workaround? Or if I am missing something?

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