singleton class C++ Singleton 模式

三个文件:socket_include.h 、socket.h 、socket.cpp;

//socket_include.h

#ifndef _SOCKETS_socket_include_H
#define _SOCKETS_socket_include_H

// class WSAInitializer is a part of the Socket class (on win32)
// as a static instance - so whenever an application uses a Socket,
// winsock is initialized
class WSAInitializer // Winsock Initializer
{
public:
 WSAInitializer() {
      if (WSAStartup(0x101,&m_wsadata))
     {
         exit(-1);
     }
 }
 ~WSAInitializer() {
      WSACleanup();
 }
private:
     WSADATA m_wsadata;
};

//Socket.h

#ifndef _SOCKETS_Socket_H
#define _SOCKETS_Socket_H

#include "socket_include.h"

class Socket
{
     ..............

     #ifdef _WIN32
     static WSAInitializer m_winsock_init; //< Winsock initialization singleton class
     #endif

     ..............

 }

//Socket.cpp

#include "Socket.h"

// statics
#ifdef _WIN32
WSAInitializer Socket::m_winsock_init; 
#endif

   通过在Socket.h中声明

     static WSAInitializer m_winsock_init

  把类WSAInitializer实现单例模式！