clock 、times 、gettimeofday

clock

NAME
       clock - Determine processor time

SYNOPSIS
       #include <time.h>

       clock_t clock(void);

DESCRIPTION
       The clock() function returns an approximation of processor time used by the program.

RETURN VALUE
       The  value  returned is the CPU time used so far as a clock_t; to get the number of seconds used,
       divide by CLOCKS_PER_SEC.  If the processor time used is not available or  its  value  cannot  be
       represented, the function returns the value (clock_t) -1.

 

times
NAME
       times - get process and waited-for child process times

SYNOPSIS
       #include <sys/times.h>

       clock_t times(struct tms *buffer);

RETURN VALUE
       Upon successful completion, times() shall return the elapsed real time, in clock ticks, since  an
       arbitrary  point in the past (for example, system start-up time). This point does not change from
       one invocation of times() within the process to another. The return value may overflow the possi‐
       ble range of type clock_t. If times() fails, (clock_t)-1 shall be returned and errno set to indi‐
       cate the error.

 

 

void exp_times()
{
 clock_t ct1,ct2;
 int i;
 double j=1.2;
 struct tms tms_start,tms_end;
 printf("sysconf( _SC_CLK_TCK ):%ld\n",sysconf( _SC_CLK_TCK ));
 printf("CLOCKS_PER_SEC: %ld\n", CLOCKS_PER_SEC);
 ct1 = times(&tms_start);
 sleep(2);
 ct2 = times(&tms_end);
 printf("takes :%ld\tuser :%ld\tsys :%ld\n",ct2 - ct1,tms_end.tms_utime - tms_start.tms_utime,
  tms_end.tms_utime - tms_start.tms_utime);

 ct1 = times(&tms_start);
 for(i=0 ;i<100000;i++)
  time(NULL);
 ct2 = times(&tms_end);
 printf("takes :%ld\tuser :%ld\tsys :%ld\n",ct2 - ct1,tms_end.tms_utime - tms_start.tms_utime,
  tms_end.tms_utime - tms_start.tms_utime);
}

 

结果：

sysconf( _SC_CLK_TCK ):100
CLOCKS_PER_SEC: 1000000
takes :200      user :0 sys :0               /*sleep 自然导致系统和用户时间为0*/
takes :14       user :4 sys :4               /**/

 

 

void exp_clock()
{
 clock_t ct1,ct2,ct3,ct4;
 int i;
 double j=1.2;
 struct tms tms_start,tms_end;

 ct1 = clock();
 sleep(2);
 ct2 = clock();
 printf("clock1 =%lf\n",(double)(ct2-ct1)/CLOCKS_PER_SEC);

 ct3 = clock();
 for(i=0 ;i<100000;i++)
  time(NULL);
 
 ct4 = clock();
 printf("clock2 =%lf\n",(double)(ct4-ct3)/CLOCKS_PER_SEC);
}

 

结果：

clock1 =0                       /*clock只是计算cpu时间，所以sleep不会计算在内，也就是0*/
clock2 =0.140000     /*对照times函数中对该循环时间的统计（takes :14       user :4 sys :4 ），此值还是合理的*/

 

void exp_gettimeoffday()
{
 struct timeval stv1 = {0};
 struct timeval stv2 = {0};
 int i;
 gettimeofday(&stv1,NULL);
 printf("sec:%ld,usec:%ld\n",stv1.tv_sec,stv1.tv_usec);
 sleep(1);
 gettimeofday(&stv1,NULL);
 printf("sec:%ld,usec:%ld\n",stv1.tv_sec,stv1.tv_usec);

 gettimeofday(&stv1,NULL);
 printf("sec:%ld,usec:%ld\n",stv1.tv_sec,stv1.tv_usec);
 for(i=0 ;i<100000;i++)
  time(NULL);
 gettimeofday(&stv2,NULL);
 printf("sec:%ld,usec:%ld\n",stv2.tv_sec,stv2.tv_usec);
 printf("cost :%lf\n",(stv2.tv_sec - stv1.tv_sec) + (double)(stv2.tv_usec - stv1.tv_usec)/1000000);
 }

 

结果：// 该函数为计算系统时间流逝。不能准确作为进程时间消耗的cpu资源。

sec:1341393579,usec:433367
sec:1341393580,usec:434199
sec:1341393580,usec:434244
sec:1341393580,usec:564779
cost :0.130535