TCP封装数据帧

void *send_data(void *arg)    //这是一个发送数据的线程
{int sockfd = init_tcp_cli("192.168.0.148",50000)  //传ip和port，port == 50000是因为大概前五万都被其它服务所占用，50000后是私人ipif(sockfd < 0){return NULL;}unsigned char pack[128] = {0};int len = 0;while(1){len = pack_net_data(data_g,pack)//data_g是一个保存数据的结构体的全局变量ssize_t size = send(sockfd,pack,len,0)if(size < 0){perror("fail send:");break;    }sleep(1)//这里是为了一秒发送一次数据}close(sockfd);return NULL;
}

初始化cli和包装数据：

int init_tcp_cli(const char *ip,unsigned short port)
{int sockfd = socket(AF_INET,SOCK_STREAM,0)if(sockfd < 0){perror("fail socket:");return -1;}struct sockaddr_in ser;ser.sin_family = AF_INET;ser.sin_port = htons(port);ser.sin_addr.s_addr = inet_addr(ip);int ret = connect(sockfd,(struct sockaddr *)&ser,sizeof(ser));if(ret < 0){perror("fail connect:");return -1;}return sockfd;
}int pack_net_data(Data_t data,unsigned char *pack)
{int i = 0;pack[i++] = 0xAA;         //帧头pack[i++] = 20;           //根据协议确定的有效数据长度memcpy(&pack[i],&data.temp,sizeof(data.temp));  //把数据拷贝到pack中i += sizeof(data.temp);   //下标往后移pack[i++] = data.tim.tm_sec; //把秒数放入pack，因为其它数据的写法都一样，就不写完了for(int j = 1; j < i;++j)  //8位和校验{pack[i] += pack[j];}++i;pack[i] = 0xBB   //帧尾++i;return i;
}