gettimeofday

http://www.169it.com/article/1638859458912479491.html

 

 Linux下gettimeofday()函数和clock()函数:精确到毫秒级的时间

  使用Linux的gettimeofday函数可以达到获取精确到毫秒级的时间，其中t1=t_start.tv_sec是公元1970年至今的时间(换算为秒）,t2=t_start.tv_usec是当前秒数下的微秒，所以将t1*1000+t2/1000可以得到当前的毫秒数。

  gettimeofday()函数原型及相关数据结构:  

 

int gettimeofday(struct timeval *tv, struct timezone *tz);

int settimeofday(const struct timeval *tv , const struct timezone *tz);

struct timeval {

    time_t      tv_sec;     /* seconds */

    SUSEconds_t tv_usec;    /* microseconds */

};

struct timezone {

    int tz_minuteswest;     /* minutes west of Greenwich */

    int tz_dsttime;         /* type of DST correction */

};

  gettimeofday()函数代码举例1

#include <stdio.h>

#include <sys/time.h>

#include <time.h>

int gettimeofday(struct timeval *tv, struct timezone *tz);

int main(int argc,char * argv[])

{

struct timeval t_start,t_end;

long cost_time = 0;

//get start time

gettimeofday(&t_start, NULL);

long start = ((long)t_start.tv_sec)*1000+(long)t_start.tv_usec/1000;

printf("Start time: %ld ms\n", start);

sleep(2);

usleep(5000);//5毫秒

//get end time

gettimeofday(&t_end, NULL);

long end = ((long)t_end.tv_sec)*1000+(long)t_end.tv_usec/1000;

printf("End time: %ld ms\n", end);

//calculate time slot

cost_time = end - start;

printf("Cost time: %ld ms\n", cost_time);

return 0;

}

  gettimeofday()函数代码举例2

struct timeval t_start,t_end;

long cost_time = 0;

//get start time

gettimeofday(&t_start, NULL);

printf("Start time: %ld us", t_start.tv_usec);

//some operation

…

//get end time

gettimeofday(&t_end, NULL);

printf("End time: %ld us", t_end.tv_usec);

//calculate time slot

cost_time = t_end.tv_usec - t_start.tv_usec;

printf("Cost time: %ld us", cost_time);

…

 

输出：

Start time: 438061 us

End time: 459867 us

Cost time: 21806 us

 

 gettimeofday()函数代码举例3:

 

#include <stdio.h>

#include <sys/time.h>

#include <time.h>

int main(int argc, char * argv[]){

    struct timeval tv;                //(1)

    while(1){

        gettimeofday(&tv, NULL);      //(2)

        printf("time %u:%un", tv.tv_sec, tv.tv_usec);

        sleep(2);

    }

    return 0;

}

 

    clock()函数返回的是程序运行过程中耗掉得process time，也就是CPU time,CLOCKS_PER_SEC用来表示一秒钟会有多少个时钟计时单元，也就是硬件滴答数。通过clock()函数获取的值可实现精确到毫秒级的时间。

   clock()函数代码举例:

int main(int argc, char **argv)

{

clock_t t1=clock();

ifstream in("data.txt");

vector<int> v;

for(int a;in>>a;v.push_back(a));

cout<<v.size()<<endl;

for(int i=0;i<v.size();i++)

cout<<v[i]<<" ";

cout<<endl;

clock_t t2=clock();

cout<<"TotalTime:"<<t2-t1<<"ms"<<endl;

}

 

 

 

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>

int main()
{
timeval tm;
gettimeofday(&tm, NULL);
printf("%u:%u", tm.tv_sec, tm.tv_usec);
sleep(3);
timeval tm1;
gettimeofday(&tm1, NULL);
printf("\n%u:%u", tm1.tv_sec, tm1.tv_usec);
// printf("\n%d", tm1-tm);
printf("\n%u%u\n", (tm1.tv_sec - tm.tv_sec) , (tm1.tv_usec-tm.tv_usec));
printf("\n%u\n", (tm1.tv_sec * 1000 + tm1.tv_usec/1000) - (tm.tv_sec * 1000 + tm.tv_usec/1000));
printf("\n%u\n", (tm1.tv_sec-tm.tv_sec)*1000 + (tm1.tv_usec-tm.tv_usec)/1000);

return 0;
}