Question

我有一个类，我定义的属性如下：

private:
    const std::string m_ip;
    bool is_connected;
    boost::asio::io_service m_io_service;
    tcp::resolver m_resolver;
    tcp::resolver::query m_query;
    tcp::resolver::iterator m_endpoint_iterator;
    tcp::socket m_socket;

构造函数实现，我定义如下：

Connection::Connection(const std::string ip) 
    : m_ip(ip)
    , is_connected(false)
    , m_resolver(tcp::resolver(&m_io_service))
    , m_query(tcp::resolver::query(m_ip, "connect_back"))
    , m_endpoint_iterator(m_resolver.resolve(m_query))
    , m_socket(tcp::socket(m_io_service))
{}

在构造函数中，我定义了几乎所有需要定义的属性。

但我有一个问题，我从来没有在一个完整的.cpp文件中：当我在构造函数中定义解析器时，编译器说我有一个错误：

/home/User/C++ Projects/Client/Network.cpp:9: error: no matching function for call to ‘boost::asio::ip::basic_resolver<boost::asio::ip::tcp>::basic_resolver(boost::asio::io_service*)’
 Connection::Connection(const std::string ip) : m_ip(ip), is_connected(false), m_resolver(tcp::resolver(&m_io_service)), m_query(tcp::resolver::query(m_ip, "connect_back")), m_endpoint_iterator(m_resolver.resolve(m_query)), m_socket(tcp::socket(m_io_service)){
                                                                                                                ^

我不明白为什么，因为我使用常规的东西！

有什么想法吗？

PS：如果我尝试从&删除m_io_service，我会收到更多错误：

/home/User/C++ Projects/Client/Network.cpp:9: error: use of deleted function ‘boost::asio::ip::basic_resolver<boost::asio::ip::tcp>::basic_resolver(boost::asio::ip::basic_resolver<boost::asio::ip::tcp>&&)’
Connection::Connection(const std::string ip) : m_ip(ip), 
is_connected(false), 
m_resolver(tcp::resolver(m_io_service)), 
m_query(tcp::resolver::query(m_ip, "connect_back")),
m_endpoint_iterator(m_resolver.resolve(m_query)),
m_socket(tcp::socket(m_io_service)){

和

/usr/include/boost/asio/ip/basic_resolver.hpp:44: error: ‘boost::asio::basic_io_object<IoObjectService, Movable>::basic_io_object(const boost::asio::basic_io_object<IoObjectService, Movable>&) [with IoObjectService = boost::asio::ip::resolver_service<boost::asio::ip::tcp>; bool Movable = false]’ is private within this context

Answer 1

添加@ Muscampester的答案，看起来你的构造函数是多余的。

Connection::Connection(const std::string ip) 
    : m_ip(ip)
    , is_connected(false)
    , m_resolver(tcp::resolver(&m_io_service))
    , m_query(tcp::resolver::query(m_ip, "connect_back"))
    , m_endpoint_iterator(m_resolver.resolve(m_query))
    , m_socket(tcp::socket(m_io_service))
{}

应该这样写：

//I changed this to const& because, while Copy Ellision *might* optimize this, it's still 
//more semantically correct to pass by const reference.
Connection::Connection(const std::string & ip) 
    : m_ip(ip)
    , is_connected(false)
      //Note that we're no longer referring to the underlying type.
    , m_resolver(m_io_service)
    , m_query(m_ip, "connect_back")
    , m_endpoint_iterator(m_resolver.resolve(m_query))
    , m_socket(m_io_service)
{}

不同之处在于您的解析器，查询和套接字对象不再是＆＃34;移动构造的＆＃34;，而是直接构造。根据你得到的第二个错误，看起来你正在使用一个版本的boost，其中这些对象不可移动/可移动构造（或者可能提升永远不会使这些类型可移动;不确定其中）。

如果您使用较旧版本的boost，请尝试更新到该库的更高版本。不管你做了什么，或者不做，你都需要更新代码，这样你就不再需要不必要的移动构建了。

Answer 2

boost::asio::ip::basic_resolver的{{3}}通过引用接受参数：

basic_resolver(boost::asio::io_service& io_service)

你已经获取了变量的地址并传递了一个指针：

m_resolver(tcp::resolver(&m_io_service))

尝试删除&。

无法在构造函数

2 个答案: