c++ - "candidate template ignored: substitution failure:"编译错误？

Question

我目前正在尝试使用 boost::asio 编写一些代码，使用 clang 3.1 进行编译。

我有一个简单的函数对象:

struct tcp_socket_match_condition
{
    template <typename TIter>
    std::pair<TIter, bool> operator()(TIter begin, TIter end) const
    {
        auto result(std::find(begin, end, '\n'));
        const bool found(result != end);
        return std::make_pair(found ? ++result : end, found);
    }
}; 

我尝试将其传递给 boost::asio::read_until 函数，如下所示:

boost::asio::read_until(socket, stream, match_condition_, error); 

生成的编译器错误看起来指出它找不到正确的函数重载。知道为什么这不起作用吗？

我提供了完整的类和编译器错误。

In file included from src/network/admin_socket.cpp:1:
In file included from include/bytes42/arthur/network/admin_socket.hpp:4:
include/bytes42/arthur/network/tcp_socket.hpp:95:21: error: no matching function for call to 'read_until'
                    boost::asio::read_until(socket, stream, match_condition_, error);
                    ^~~~~~~~~~~~~~~~~~~~~~~
src/network/admin_socket.cpp:81:10: note: in instantiation of member function
      'bytes42::arthur::network::tcp_socket<bytes42::arthur::network::detail::tcp_socket_match_condition>::listen' requested here
        socket_.listen();
                ^
/usr/local/include/boost/asio/impl/read_until.hpp:47:13: note: candidate function [with SyncReadStream =
      boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, Allocator =
      std::__1::allocator<char>] not viable: no known conversion from 'bytes42::arthur::network::detail::tcp_socket_match_condition' to 'char' for 3rd
      argument;
std::size_t read_until(SyncReadStream& s,
            ^
/usr/local/include/boost/asio/impl/read_until.hpp:138:13: note: candidate function [with SyncReadStream =
      boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, Allocator =
      std::__1::allocator<char>] not viable: no known conversion from 'bytes42::arthur::network::detail::tcp_socket_match_condition' to
      'const std::string' (aka 'const basic_string<char, char_traits<char>, allocator<char> >') for 3rd argument;
std::size_t read_until(SyncReadStream& s,
            ^
/usr/local/include/boost/asio/impl/read_until.hpp:203:13: note: candidate function [with SyncReadStream =
      boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, Allocator =
      std::__1::allocator<char>] not viable: no known conversion from 'bytes42::arthur::network::detail::tcp_socket_match_condition' to
      'const boost::regex' (aka 'const basic_regex<char, regex_traits<char> >') for 3rd argument;
std::size_t read_until(SyncReadStream& s,
            ^
/usr/local/include/boost/asio/impl/read_until.hpp:260:13: note: candidate template ignored: substitution failure [with SyncReadStream =
      boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, Allocator =
      std::__1::allocator<char>, MatchCondition = bytes42::arthur::network::detail::tcp_socket_match_condition]
std::size_t read_until(SyncReadStream& s,
            ^
/usr/local/include/boost/asio/impl/read_until.hpp:312:20: note: candidate template ignored: substitution failure [with SyncReadStream =
      boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, Allocator =
      std::__1::allocator<char>, MatchCondition = bytes42::arthur::network::detail::tcp_socket_match_condition]
inline std::size_t read_until(SyncReadStream& s,
                   ^
/usr/local/include/boost/asio/impl/read_until.hpp:37:20: note: candidate function template not viable: requires 3 arguments, but 4 were provided
inline std::size_t read_until(SyncReadStream& s,
                   ^
/usr/local/include/boost/asio/impl/read_until.hpp:93:20: note: candidate function template not viable: requires 3 arguments, but 4 were provided
inline std::size_t read_until(SyncReadStream& s,
                   ^
/usr/local/include/boost/asio/impl/read_until.hpp:193:20: note: candidate function template not viable: requires 3 arguments, but 4 were provided
inline std::size_t read_until(SyncReadStream& s,
                   ^
1 error generated.
make: *** [build/src/network/admin_socket.o] Error 1

类:

    template <typename TMatchCondition>
    class tcp_socket
    {
        public:
            typedef std::function<std::string(const std::string&)> data_callback;

        public:
            tcp_socket(
                const unsigned short port,
                TMatchCondition match_condition,
                data_callback callback);

            void listen();
            void stop();

        private:
            tcp_socket(const tcp_socket&)   = delete;
            tcp_socket(tcp_socket&&)        = delete;

            tcp_socket& operator=(const tcp_socket&) = delete;
            tcp_socket& operator=(tcp_socket&&)      = delete;

        private:
            const utils::entry_exit         entry_exit_;
            boost::asio::io_service         service_;
            boost::asio::ip::tcp::acceptor  acceptor_;
            TMatchCondition                 match_condition_;
            data_callback                   callback_;
    };


    template <typename TMatchCondition>
    tcp_socket<TMatchCondition>::tcp_socket(
        const unsigned short port,
        TMatchCondition match_condition,
        data_callback callback)
        : entry_exit_("tcp_socket:" + std::to_string(port))
        , acceptor_(service_, boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), port))
        , match_condition_(match_condition)
        , callback_(callback) {}

    template <typename TMatchCondition>
    void tcp_socket<TMatchCondition>::listen()
    {
        const auto port(acceptor_.local_endpoint().port());
        const std::string port_str(std::to_string(port));

        while(acceptor_.is_open())
        {
            boost::system::error_code error;

            utils::entry_exit ee("Listening on port " + port_str);

            boost::asio::ip::tcp::socket socket(service_);
            acceptor_.accept(socket, error);

            if(error)
            {
                if(error != boost::asio::error::bad_descriptor)
                {
                    LOG(ERROR)
                        << "An error occured while trying to accept a client connection; error="
                        << error.message();

                    sleep(1);  // don't want to flood logs
                }
            }
            else
            {
                while(socket.is_open())
                {
                    boost::asio::streambuf stream;
                    boost::asio::read_until(socket, stream, match_condition_, error);

                    const std::string msg(
                        (std::istreambuf_iterator<char>(&stream)),
                        std::istreambuf_iterator<char>());

                    LOG(INFO) << "Received message: " << msg;

                    boost::asio::write(
                        socket,
                        boost::asio::buffer(callback_(msg)),
                        error);

                    if(error)
                    {
                        if(error != boost::asio::error::broken_pipe)
                        {
                            LOG(ERROR)
                                << "Error whilst writing response, closing client connection: "
                                << error.message();
                        }

                        socket.close();

                        sleep(1);  // don't want to flood logs
                    }
                }
            }
        }
    }


    template <typename TMatchCondition>
    void tcp_socket<TMatchCondition>::stop()
    {
        boost::system::error_code error;
        acceptor_.close(error);

        if(error)
        {
            LOG(ERROR) << "Error whilst stopping TCP socket; error=" << error.message();
        }
    }                                

Answer 1

我认为您没有发布完整代码，但问题似乎是匹配条件:您是否指定使用 boost::is_match_condition您的 tcp_socket_match_condition 是匹配条件吗？