Errore del linker durante la compilazione dell'esempio boost.asio

Question

Sto cercando di imparare un po 'C++ e Boost.Asio. Sto cercando di compilare il seguente esempio di codice:

#include <iostream> 
#include <boost/array.hpp> 
#include <boost/asio.hpp> 

using boost::asio::ip::tcp; 

int main(int argc, char* argv[]) 
{ 
    try 
    { 
    if (argc != 2) 
    { 
     std::cerr << "Usage: client <host>" << std::endl; 
     return 1; 
    } 

    boost::asio::io_service io_service; 

    tcp::resolver resolver(io_service); 
    tcp::resolver::query query(argv[1], "daytime"); 
    tcp::resolver::iterator endpoint_iterator = resolver.resolve(query); 
    tcp::resolver::iterator end; 

    tcp::socket socket(io_service); 
    boost::system::error_code error = boost::asio::error::host_not_found; 
    while (error && endpoint_iterator != end) 
    { 
     socket.close(); 
     socket.connect(*endpoint_iterator++, error); 
    } 
    if (error) 
     throw boost::system::system_error(error); 

    for (;;) 
    { 
     boost::array<char, 128> buf; 
     boost::system::error_code error; 

     size_t len = socket.read_some(boost::asio::buffer(buf), error); 

     if (error == boost::asio::error::eof) 
     break; // Connection closed cleanly by peer. 
     else if (error) 
     throw boost::system::system_error(error); // Some other error. 

     std::cout.write(buf.data(), len); 
    } 
    } 
    catch (std::exception& e) 
    { 
    std::cerr << e.what() << std::endl; 
    } 

    return 0; 
} 

Con la seguente riga di comando:

g++ -I /usr/local/boost_1_42_0 a.cpp 

e getta un errore poco chiaro:

/tmp/ccCv9ZJA.o: In function `__static_initialization_and_destruction_0(int, int)': 
a.cpp:(.text+0x654): undefined reference to `boost::system::get_system_category()' 
a.cpp:(.text+0x65e): undefined reference to `boost::system::get_generic_category()' 
a.cpp:(.text+0x668): undefined reference to `boost::system::get_generic_category()' 
a.cpp:(.text+0x672): undefined reference to `boost::system::get_generic_category()' 
a.cpp:(.text+0x67c): undefined reference to `boost::system::get_system_category()' 
/tmp/ccCv9ZJA.o: In function `boost::system::error_code::error_code()': 
a.cpp:(.text._ZN5boost6system10error_codeC2Ev[_ZN5boost6system10error_codeC5Ev]+0x10): undefined reference to `boost::system::get_system_category()' 
/tmp/ccCv9ZJA.o: In function `boost::asio::error::get_system_category()': 
a.cpp:(.text._ZN5boost4asio5error19get_system_categoryEv[boost::asio::error::get_system_category()]+0x7): undefined reference to `boost::system::get_system_category()' 
/tmp/ccCv9ZJA.o: In function `boost::asio::detail::posix_thread::~posix_thread()': 
a.cpp:(.text._ZN5boost4asio6detail12posix_threadD2Ev[_ZN5boost4asio6detail12posix_threadD5Ev]+0x1d): undefined reference to `pthread_detach' 
/tmp/ccCv9ZJA.o: In function `boost::asio::detail::posix_thread::join()': 
a.cpp:(.text._ZN5boost4asio6detail12posix_thread4joinEv[boost::asio::detail::posix_thread::join()]+0x25): undefined reference to `pthread_join' 
/tmp/ccCv9ZJA.o: In function `boost::asio::detail::posix_tss_ptr<boost::asio::detail::call_stack<boost::asio::detail::task_io_service<boost::asio::detail::epoll_reactor<false> > >::context>::~posix_tss_ptr()': 
a.cpp:(.text._ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_15task_io_serviceINS1_13epoll_reactorILb0EEEEEE7contextEED2Ev[_ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_15task_io_serviceINS1_13epoll_reactorILb0EEEEEE7contextEED5Ev]+0xf): undefined reference to `pthread_key_delete' 
/tmp/ccCv9ZJA.o: In function `boost::asio::detail::posix_tss_ptr<boost::asio::detail::call_stack<boost::asio::detail::task_io_service<boost::asio::detail::epoll_reactor<false> > >::context>::posix_tss_ptr()': 
a.cpp:(.text._ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_15task_io_serviceINS1_13epoll_reactorILb0EEEEEE7contextEEC2Ev[_ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_15task_io_serviceINS1_13epoll_reactorILb0EEEEEE7contextEEC5Ev]+0x22): undefined reference to `pthread_key_create' 
collect2: ld returned 1 exit status 

Come posso risolvere il problema ?

Answer 1

è necessario collegarsi a libboost_system e apparentemente anche contro libboost_thread.

g++ -I /usr/local/boost_1_42_0 -lboost_system -lboost_thread a.cpp 

in caso di librerie multi-threaded:

g++ -I /usr/local/boost_1_42_0 -lboost_system-mt -lboost_thread-mt a.cpp 

Answer 2

Avete costruito le librerie Boost o stai cercando di fare questo con una configurazione di testa-solo? L'errore sembra che manchi la libreria boost_system, il che suggerirebbe che il linker non possa trovare la libreria pre-costruita.

Answer 3

È necessario indicare a g ++ dove sono i file di intestazione, dove sono le librerie e quale libreria si sta utilizzando, ad es. sul mio sistema:

g++ -I /opt/local/include -L /opt/local/lib -lboost_system-mt -lboost_thread-mt a.cpp 

dove -I dice g ++ in cui i file di intestazione sono e -L dice g ++ in cui le librerie reali sono e -lboost_thread-MT è la libreria che voglio collegare contro nella cartella -L.