提升::不满足 ASIO 读取处理程序类型要求

Question

我正在尝试实现一个读取标头处理程序作为成员函数来处理传入的数据。但是在编译过程中，我被告知不满足类型要求。

我已经检查了提升文档，函数签名似乎很好。我看不出有什么不同。但是，boost 不接受处理程序为有效。

.cpp文件：

void tcpclient::read_data() {
    char buffer_[1];
    boost::asio::async_read(_socket, boost::asio::buffer(buffer_, HEADER_LEN),
                            std::bind(&tcpclient::handle_read_header, this,
                                      boost::asio::placeholders::error,
                                      boost::asio::placeholders::bytes_transferred));
}

void tcpclient::handle_read_header(const boost::system::error_code &error, std::size_t bytes_transferred) {
    if (!error) {
        logger::log_info("Read " + std::to_string(bytes_transferred) + " bytes.");
    } else {
        logger::log_error("Failed to read header");
        _socket.close();
    }
}

.h 文件：

void handle_read_header(const boost::system::error_code &error, std::size_t bytes_transferred);
    void read_data();
    boost::asio::ip::tcp::socket _socket;

我希望代码可以很好地接受处理程序签名，但系统提示我：

/usr/include/boost/asio/impl/read.hpp: In instantiation of ‘typename boost::asio::async_result<typename std::decay<WriteHandler>::type, void(boost::system::error_code, long unsigned int)>::return_type boost::asio::async_read(AsyncReadStream&, const MutableBufferSequence&, ReadHandler&&, typename std::enable_if<boost::asio::is_mutable_buffer_sequence<MutableBufferSequence>::value>::type*) [with AsyncReadStream = boost::asio::basic_stream_socket<boost::asio::ip::tcp>; MutableBufferSequence = boost::asio::mutable_buffers_1; ReadHandler = std::_Bind<void (tcpclient::*(tcpclient*, boost::arg<1> (*)(), boost::arg<2> (*)()))(const boost::system::error_code&, long unsigned int)>; typename boost::asio::async_result<typename std::decay<WriteHandler>::type, void(boost::system::error_code, long unsigned int)>::return_type = void; typename std::enable_if<boost::asio::is_mutable_buffer_sequence<MutableBufferSequence>::value>::type = void]’:
/home/void/Documents/Development/SocketTest/SocketTest/networking/tcpclient.cpp:55:84:   required from here
/usr/include/boost/asio/impl/read.hpp:446:3: error: static assertion failed: ReadHandler type requirements not met
   BOOST_ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/boost/asio/impl/write.hpp:430:3: error: no match for call to ‘(std::_Bind<void (tcpclient::*(tcpclient*, boost::arg<1> (*)(), boost::arg<2> (*)()))(const boost::system::error_code&, long unsigned int)>) (const boost::system::error_code&, const long unsigned int&)’
   BOOST_ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Answer 1

将boost::bind与boost::asio::placeholders::..

一起使用

boost::bind(&tcpclient::handle_read_header, this,
                                  boost::asio::placeholders::error,
                                  boost::asio::placeholders::bytes_transferred));

或std::placeholders::_1/_2 std::bind：

std::bind(&tcpclient::handle_read_header, this,
                                  std::placeholders::_1,
                                  std::placeholders::_2));