linux time

uint32_t midtime;
static struct timeval startstart,midmid;
while (ros::ok())
{
　　 gettimeofday(&startstart,NULL);
　　usleep(10000); //10ms
　　gettimeofday(&midmid,NULL);
　　midtime = 1000000*(midmid.tv_sec - startstart.tv_sec)+(midmid.tv_usec - startstart.tv_usec);//us,1s=10^6us=10^3ms
　　printf("midtime = %u\n",midtime);
}