//定义枚举：enmu state{CLOSED，//没有连接SYN-SENT，//发送了syn，等代服务器ackACK_RECEIVE,//接到服务器ackSYNACK_SEND,//恢复服务器的ack，确认ESTABLISHED，//成功建立}//定义你自己的用udp连接函数int newconnect( int sd, const struct sockaddr * sa, int namelen ){    int err = -1;    int state = CLOSED；    char ** buff[128] = {"syn","synack"};    char buffrom[128];    memset(buff,0,128);    while(true)//开始状态机转换        {        if( state == ESTABLISHED )            break;        switch(state)        {            case CLOSED:                err = sendto( sd, buff[0], strlen(buff[0]), 0, sa, namelen );                if( err == SOCKET_ERROR )                    goto error；                state = SYN-SENT；                break;            case SYN-SENT:                err = recvfrom( sd, buffrom, strlen(buffrom), sa, namelen );                if( err == SOCKET_ERROR )                    goto error；                if( !strcmp(buffom,"ack",3) )                    state = ACK_RECEIVE；                break；            case ACK_RECEIVE:                err = sendto( sd, buff[1], strlen(buff[1]), 0, sa, namelen );                if( err == SOCKET_ERROR )                    goto error；                state = ESTABLISHED:                break;            case ESTABLISHED:                break;            default:                break;        }                }    return sd;err:    closesocket(sd);    return NULL;}