自认为对C++比较熟悉，突然看到一些奇怪的代码（在看网上下载的代码Sockets）：
class SocketAddress
{
public:
virtual ~SocketAddress() {} /** Get a pointer to the address struct. */
virtual operator struct sockaddr *() = 0; /** Get length of address struct. */
virtual operator socklen_t() = 0; /** Compare two addresses. */
virtual bool operator==(SocketAddress&) = 0; /** Set port number.
\param port Port number in host byte order */
virtual void SetPort(port_t port) = 0; /** Get port number.
\return Port number in host byte order. */
virtual port_t GetPort() = 0; /** Set socket address.
\param sa Pointer to either 'struct sockaddr_in' or 'struct sockaddr_in6'. */
virtual void SetAddress(struct sockaddr *sa) = 0; /** Convert address to text. */
virtual std::string Convert(bool include_port) = 0; /** Reverse lookup of address. */
virtual std::string Reverse() = 0; /** Get address family. */
virtual int GetFamily() = 0; /** Address structure is valid. */
virtual bool IsValid() = 0; /** Get a copy of this SocketAddress object. */
virtual std::auto_ptr<SocketAddress> GetCopy() = 0;
};
奇怪的代码：
/** Get a pointer to the address struct. */
virtual operator struct sockaddr *() = 0; /** Get length of address struct. */
virtual operator socklen_t() = 0;
最后搜了一下，才知道是对 类型转换 的重载！
socklen_t 是 int 类型 ；
声明：operator XX(); 无返回值，XX就是某个类型；
用法：XX a = (XX)obj; 假设上边SocketAddress非abstract类，例如：SocketAddress sa; int a = (socklen_t)sa; 也就是此时会调用原成员函数operator XX(); 一般返回XX类型值，可以理解成类型转换的重载！
另外：我竟不知道一个自定义类的 构造函数可以用作隐形的类型转换，例如：Class A { A(int i) { val = i}; private int val;} , A a = 5; 解：5 首先通过构造函数A(int)隐形的转换为A类型，然后调用默认的operator=赋值函数，赋值给a；