July 2009 - Boost-users - lists.preview.boost.org

General: <unresolved overloaded function type>
by Etienne Philip Pretorius 28 Jul '09

28 Jul '09

Hello List, Just a general question: I am trying to use boost::asio::async_read_until with a these templated functions: template<typename D> struct entity { template<typename T> std::pair<T,bool> operator()( T begin, T end ) { if(begin == end) { return std::make_pair<end,false>; } return static_cast<D*>(this)->impl(begin,end); }; }; /* http://www.w3.org/TR/REC-xml/#NT-S */ struct white_space : entity<white_space> { template<typename T> std::pair<T,bool> impl( T begin, T end ) { for(; begin != end; begin++) { if(*begin == 0x09u || *begin == 0x0Au || *begin == 0x0Du || *begin == 0x20u) { continue; }else{ return std::make_pair<begin,false>; } } return std::make_pair<end,true>; }; }; I get the following error: xml.hpp:146: error: conversion from ‘<unresolved overloaded function type>’ to non-scalar type ‘std::pair<boost::asio::buffers_iterator<boost::asio::const_buffers_1, char>, bool>’ requested At every line that I have a return defined... Could someone please explain to me what I have done wrong here.... Thank you, Etienne

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[program_options] detecting if "arguments" are passed
by Christoph Duelli 28 Jul '09

28 Jul '09

I am using Boost.ProgramOptions to parse my command line options. By default, I an exception is thrown when an unknown option is passed. So far, so good. Suppose I have a program p that takes only the option --help - and nothing else, esp. not a "positional option" or "arguments". I.e. I would like to croak a message to the user if she call something like p /tmp/x ProgramOptions does croak when I call "p -v", but not when I call "p /tmp/x". Question: What is the recommended way to catch unwanted (or forbidden) arguments (not options!)? (I know I can define a positional like --input-file and then check if any of those are present. But that seems quite awkward for such a "simple" thing.) Best regards Christoph

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[newbie] Boost 1.39 in Mac XCode get "error: attempt to copy-construct an iterator from a singular iterator."
by Victor Tsang 28 Jul '09

28 Jul '09

Hi, I'm new to boost. It seems that the coding of boost library is not very clean as it makes the debug code aborted by generating a runtime error like this: "error: attempt to copy-construct an iterator from a singular iterator.". Here are the steps to reproduce the fault: I downloaded the source and install the things to /usr/local/include as well as /usr/local/lib. I test the code by creating a "C++ Tool" project in XCode. 1. Create a new C++ Tool project. 2. Add the header search path /usr/local/include/boost-1_39 and library search path /usr/local/lib into the project. 3. Add "Other Linker Flags" "-lboost_system-xgcc40-mt" in the project setting. 4. Edit the main.cpp as below: #include <iostream> #include<boost/asio.hpp> int main (int argc, char * const argv[]) { boost::asio::io_service io_service; boost::asio::ip::tcp::acceptor acceptor(io_service); std::cout<<"acceptor instantiated."<<std::endl; return 0; } 5. Build and run. Check out the result from the Console window as captured below: [Session started at 2009-07-28 16:00:10 +0800.] * /Developer/SDKs/MacOSX10.5.sdk/usr/include/c++/4.0.0/debug/safe_iterator.h:127: * * error: attempt to copy-construct an iterator from a singular iterator.* ** *Objects involved in the operation:* *iterator "this" @ 0x0x100480 {* *type = N11__gnu_debug14_Safe_iteratorIN10__gnu_norm14_List_iteratorISt4pairIiPN5boost4asio6detail16reactor_op_queueIiE7op_baseEEEEN15__gnu_debug_def4listISB_SaISB_EEEEE (mutable iterator);* * state = singular;* *}* *iterator "other" @ 0x0xbffff364 {* *type = N11__gnu_debug14_Safe_iteratorIN10__gnu_norm14_List_iteratorISt4pairIiPN5boost4asio6detail16reactor_op_queueIiE7op_baseEEEEN15__gnu_debug_def4listISB_SaISB_EEEEE (mutable iterator);* * state = singular;* *}* [Session started at 2009-07-28 16:00:10 +0800.] GNU gdb 6.3.50-20050815 (Apple version gdb-966) (Tue Mar 10 02:43:13 UTC 2009) Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-apple-darwin".sharedlibrary apply-load-rules all Attaching to process 3497. The Debugger Debugger is attaching to process It generates a runtime error "error: attempt to copy-construct an iterator from a singular iterator.". However, if I compile the code in terminal: g++ -o test -g -Wall main.cpp -lboost_system-xgcc40-mt It runs okay without any runtime error. Regards, Victor Tsang

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Re: [Boost-users] [Boost.CircularBuffer] begin()/end() arithmetic not working out quite right
by David Baird 27 Jul '09

27 Jul '09

Hi Jan, Thanks for your reply and sorry for taking so long to respond. I am a bit confused by your response. I never did expect begin() to move forward after push_back(). In my original post, what I said is that I expect begin() will remain constant and that **end() will move forward** each time push_back() is called. My main question is this: why does end() remain constant when push_back() is called on a circular_buffer? In other words, why does this assertion fail?: circular_buffer<int> buf(8); circular_buffer<int>::iterator a; circular_buffer<int>::iterator b; a = buf.end(); buf.push_back(1); b = buf.end(); assert(a != b); // fails If I use an STL vector instead of circular_buffer, I get exactly the results I expect (as along as I call .reserve() on it prior, so that iterators are not invalidated by a realloc). -David On Thu, Jun 11, 2009 at 1:58 AM, Jan Gaspar<jano_gaspar(a)yahoo.com> wrote: > > Hi David, > > you just cannot rely on this. I don't think standard says anything about begin() moving forward after push_back(). Correct me if I'm wrong. > > The way how it is implemented is that if the circular_buffer is empty begin() returns the same iterator as end(). > > There is also a note about iterator invalidation for push_back(): > "Does not invalidate any iterators with the exception of iterators pointing to the overwritten element." > > It means iterator 'a' in your first example will point to the same element as it was before calling push_back() - which is end(). This explains the behaviour you are describing. > > Regards, > > Jan > > > > > ----- Original Message ---- > From: David Baird <dhbaird(a)gmail.com> > To: Jan Gaspar <jano_gaspar(a)yahoo.com>; boost-users(a)lists.boost.org > Sent: Thursday, 11 June, 2009 1:01:54 > Subject: [Boost.CircularBuffer] begin()/end() arithmetic not working out quite right > > Hi, > > Firstly, thanks for the work on a circular buffer. This is very > useful since many of my applications require it. I am having a > problem though... > > I am using Boost 1.38.0. When I call push_back(), the iterator math > makes it appear that begin() moves backwards and end() remains > constant. (Based on other STL libraries, I expect that begin() will > remain constant and end() will keep advancing as I call push_back()). > > In other words, this assertion fails (but I expect it to succeed): > > circular_buffer<int> buf(8); > circular_buffer<int>::iterator a; > circular_buffer<int>::iterator b; > a = buf.begin(); > buf.push_back(1); > b = buf.begin(); > assert(a == b); // Fails!! > > Also, this code fails too (but I expect it to succeed): > > circular_buffer<int> buf(8); > circular_buffer<int>::iterator a; > circular_buffer<int>::iterator b; > a = buf.end(); > buf.push_back(1); > b = buf.end(); > assert(a != b); // Also fails! > > Below is a full example that you can compile and try out: > > #include <boost/circular_buffer.hpp> > #include <stdio.h> > > int > main () > { > typedef boost::circular_buffer<int> buf_type; > // Instead of "end" moving ahead, "begin" is moving backwards when // > // using "push_back". > { > buf_type buf1(1024); > buf_type::iterator a; > buf_type::iterator b; > a = buf1.end(); > buf1.push_back(1); > buf1.push_back(2); > b = buf1.end(); > printf ("%d\n", a == b); > // >>> > // got: 1 > // expected: 0 > printf ("%d, %d\n", a-buf1.begin(), b-buf1.begin()); > // >>> > // got: 2, 2 > // expected: 0, 2 > } > { > buf_type buf2(1024); > buf_type::iterator c; > buf_type::iterator d; > c = buf2.begin(); > buf2.push_back(1); > buf2.push_back(2); > d = buf2.begin(); > printf ("%d\n", c == d); > // >>> > // got: 0 > // expected: 1 > // (i.e. "begin()" is not still pointing to first item!! > // This is incorrect, isn't it?) > printf ("%d, %d\n", buf2.end()-c, buf2.end()-d); > // >>> > // got: 0, 2 > // expected: 2, 2 > } > return 0; > } > > > Thanks, > David > > > > >

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determining the number of collumns in a .csv file
by Sean Farrow 27 Jul '09

27 Jul '09

Hi: I am currently using the boost.spirit example to process a csv file. Rather than stuffing all values in to a vector as the example does what I'dx like to do is to determine how many columns exist and stuff all values in to a multi-dimensional array. What is the best way of doing this? Cheers Sean.

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[Units] help with type-safe unit-specific conversions
by Justin Leonard 27 Jul '09

27 Jul '09

I have been playing with Boost.Units as part of a work project recently, and I am not sure what the best approach to "demarshalling" values in a specific unit. For example, I would like to do something like: using namespace boost::units; struct A { enum { feet, kilometers }; quantity<si::length> some_length; double foo(int type) { switch(type) { case feet: return quantity<feet>(some_length).value(); case kilometers: return quantity<kilometers>(some_length).value(); } } }; This approach is necessary for passing values to external libraries which do not (and probably will never) use Boost.Units. Is conversion_factor the best approach, or is there a way to achieve this implicitly using the type system? Thanks Justin

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filesystem: create_directory unexpected exception
by ciju john 27 Jul '09

27 Jul '09

Platform: Windows XP Pro Boost version: 1.38 1.39 (BoostPro binary release) try { boost::filesystem::create_directory ("C:\Program Files\hello123"); } catch (const boost::filesystem::basic_filesystem_error<char*>& ) { std::cerr << "Directory creation failed" << std::endl; } The above code crashes if user doesn't have root permission. I assume some exception is being thrown as catch (...) catches whatevers being thrown. The documentation says "Throws: basic_filesystem_error<Path> if Effects fails for any reason other than because the directory already exists." The requested directory "C:\Program Files\hello123" doesn't exist, so I should have caught a boost::filesystem::basic_filesystem_error. Is this a known issue or am I the only one seeing this? thanks, john

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New Boost.Build tutorial
by Boris Schaeling 27 Jul '09

27 Jul '09

As I started to use Boost.Build recently I wrote everything down what I learnt and what is partly missing in the documentation. The article can be found at: http://www.highscore.de/cpp/boostbuild/ There is also a reference of rules and features. If someone likes me to add more rules and features just send me a mail (including a description as I don't know all rules and features myself :). This will not only make the reference more complete. I might also learn something new which will help me to use Boost.Build more efficiently. By the way, there is also a section about best practices which I'm also interested in. Boris

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Why boost::asio doesn't work???
by Gotch＠ 27 Jul '09

27 Jul '09

I'm starting using Boost::Asio. I tried to write a simple class to send and receive asynchronously UDP datagrams, following the boost::asio tutorial. The class compiles fine, but it's not working and comes out with an exception about a mutex (which shouldn't be involved I guess). Basically there are two methods: one starts an async_receive_from and the other send packets asynchronously. I first start the receiver, then I try to send a packet to localhost (127.0.0.1). But nothing happens. Here is the code, maybe you may know what's wrong. With the following class the header: namespace msgSrv { class endPoint { public: asio::ip::udp::endpoint ep; endPoint(std::string ip, int port); }; class msgSrv { private: asio::ip::udp::socket *asioSocket; asio::io_service *asioIoService; int listenPort; boost::array<char, 1> rcvBuff; asio::ip::udp::endpoint lastRcvdPcktEndp; char * sbuff; public: boost::condition_variable cond; boost::mutex mut; msgSrv(int listenPort); virtual ~msgSrv(); void start(); void pckRcvd(const asio::error_code& error, std::size_t bytes_transferred); void sendTo(const char* buff, int len, endPoint ep); void sendHnd(const asio::error_code& error, std::size_t bytes_transferred); }; } the .cpp #include "msgSrv.h" namespace msgSrv { endPoint::endPoint(const std::string ip, int port) { asio::ip::address addr = asio::ip::address::from_string(ip); ep = asio::ip::udp::endpoint(addr, port); } msgSrv::msgSrv(int listenPort) { // TODO Auto-generated constructor stub this->listenPort = listenPort; try { asioIoService = new asio::io_service(); asioSocket = new asio::ip::udp::socket(*asioIoService, asio::ip::udp::endpoint(asio::ip::udp::v4(), listenPort)); //new asio::ip::udp::socket_(*asioIoService, udp::endpoint(udp::v4(), listenPort)); } catch (std::exception &e) { std::cerr << "Error initializing ioservice or socket:" << e.what(); } asioIoService->run(); } msgSrv::~msgSrv() { // TODO Auto-generated destructor stub delete asioIoService; delete asioSocket; } void msgSrv::start() { asioSocket->async_receive_from(asio::buffer(rcvBuff), lastRcvdPcktEndp, boost::bind(&msgSrv::pckRcvd, this, asio::placeholders::error, asio::placeholders::bytes_transferred)); } void msgSrv::pckRcvd(const asio::error_code& error, std::size_t bytes_transferred) { std::cout << "Rcvd! " << lastRcvdPcktEndp.address().to_string() << ":" << lastRcvdPcktEndp.port() << "\n"; } void msgSrv::sendTo(const char* buff, int len, endPoint ep) { sbuff = new char[len]; mempcpy(sbuff, buff, len); asioSocket->async_send_to(asio::buffer(sbuff, len), ep.ep, boost::bind( &msgSrv::sendHnd, this, asio::placeholders::error, asio::placeholders::bytes_transferred)); } void msgSrv::sendHnd(const asio::error_code& error, std::size_t bytes_transferred) { std::cout << "Snt!\n"; delete sbuff; } } and the following "main" file: int main() { msgSrv::msgSrv aa(4450); aa.start(); msgSrv::endPoint ep("127.0.0.1", 4450); std::string a("Prova!"); int len = a.length(); aa.sendTo(a.c_str(), len, ep); std::cout << "sent...\n"; std::cout << "notified...\n"; } all I get is: terminate called after throwing an instance of 'asio::system_error' what(): mutex: Invalid argument sent... notified... What's wrong?? I tried even to put a while(1) in the main, to see if something happens... I even tried to put a condition in the main that is unlocked by the receive handler... all remains locked... So what??? No idea!

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getting a handle to another connection?
by Ozgur Ozturk 27 Jul '09

27 Jul '09

Hi, I need to send ip information of a client to the other one (as they will connect to each other directly now). I used async echo server sample <http://www.boost.org/doc/libs/1_39_0/doc/html/boost_asio/example/echo/async…>as a starting point. I guess sessions are recorded in io_service instance, since in the server constructor when we create session, we pass io_service to it. session* new_session = new session(io_service_); Can I get information of connected sessions from io_service? (or any other recommendations on how to better design it?) To expand my question: I am implementing a chat server, but the chats will not go over the server (is it a bad idea?). many clients connects, I keep their status (online or not) in a database. when A wants to talk to B, I need to pass request to B, how can I get a handle to my connection to B while I am in the instance of session with A? I am still not sure I understand io_service concept. Is this proactor thing similar to observer pattern? When we pass io_service as a parameter to something, are we registering it to be observed in io_service? Thanks in advance, (*Thanks for all the previous answers too, *I have made significant progress...) Best regards, Ozgur (Oscar) Ozturk www.DrOzturk.com Phone: +1 (908) DROZGUR i.e, +1 (908) 376-9487

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