gettimeofday实现微秒计时

微秒计时实现如下：

long time_long=0;       //初始时间
double time_double=0;   //与初始时间的差值（计时时间）

struct timeval tv;
gettimeofday(&tv,NULL);
printf("microsecond:%ld\n",tv.tv_sec*1000000 + tv.tv_usec);  //微秒，*1000000+usec是为了整合成整数，再除1000000可以成为附带微秒的时间
time_long=tv.tv_sec*1000000 + tv.tv_usec;

sleep(3); //程序睡三秒后对比
printf("3s later:\n");

gettimeofday(&tv,NULL);
time_double=(tv.tv_sec*1000000 + tv.tv_usec - time_long)*1.000000/1000000 ;
printf("microsecond:%lf\n",time_double);  //微秒

sleep(3); //程序睡三秒后对比
printf("3s later:\n");

gettimeofday(&tv,NULL);
time_double=(tv.tv_sec*1000000 + tv.tv_usec - time_long)*1.000000/1000000 ;
printf("microsecond:%lf\n",time_double);  //微秒