socket（）套接字创建失败

Input::Input(uint16_t port, uint16_t gpsPort)
{
  socketForLidar = -1;//00
  socketForLidar = socket(PF_INET, SOCK_DGRAM, 0);
  //if (socketForLidar == -1)//00
  if (INVALID_SOCKET == socketForLidar)
  {
    perror("socket"); // TODO: perror errno
    return;
  }
  ...
  ...
}

运行发现程序进入了if (INVALID_SOCKET == socketForLidar)----即socket（）创建套接字失败！
后来想到之前学mfc网络编程最一开始是要加载套接字库，设置套接字版本信息等：
于是添加如下信息：

Input::Input(uint16_t port, uint16_t gpsPort)
{
//首先加载套接字库信息
    WORD wVersionRequested;
    WSADATA wsaData;
    int err;
    wVersionRequested = MAKEWORD(2, 1); //高位字节存储副版本号, 低位字节存储主版本号
    err = WSAStartup(wVersionRequested, &wsaData);//WSAStartup，即WSA(Windows Sockets Asynchronous，Windows异步套接字)的启动命令
    if (err != 0)
    {
        return;
    }

    if (LOBYTE(wsaData.wVersion) != 2 || HIBYTE(wsaData.wVersion) != 1)//高位字节和低位字节不正确
    {
        WSACleanup();
        return;
    }
  
  socketForLidar = -1;//00
  socketForLidar = socket(PF_INET, SOCK_DGRAM, 0);

  //if (socketForLidar == -1)//00
  if (INVALID_SOCKET == socketForLidar)
  {
    perror("socket"); // TODO: perror errno
    return;
  }
  ......
  ......
}

综上：socket（）返回INVALID_SOCKET，一般是在程序运行前没有执行WSAStartup()操作！Winsock未初始化或初始化失败！