函数原型：

#include <sys/times.h>
clock_t times (struct tms * buf );

函数功能：
获取进程时间。

说明：
    times() 函数返回从过去一个任意的时间点所经过的时钟数。返回值可能会超出 clock_t  (一般为 long 型) 的范围(溢出)。如果发生错误，则返回 (clock_t ) -1 类型，然后设置相应的 errno 值。

系统每秒的时钟可以通过 sysconf(_SC_CLK_TCK); 函数获得。关于 sysconf() 函数的详细信息见：http://blog.sina.com.cn/s/blog_590be5290100ncty.html

上面 _SC_CLK_TCK 的值为 2，因为它在 /usr/include/bits/confname.h 头文件的一个枚举类型里定义。

struct tms 结构体定义在 <sys/times.h> 头文件里，具体定义如下：

struct tms
  {
    clock_t tms_utime ;         
    clock_t tms_stime ;         

    clock_t tms_cutime ;        
    clock_t tms_cstime ;        
  };

实例验证 times() 函数
测试代码：

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

int main ()
{
    struct tms time_buf_head , time_buf_end ;
    long   tck = 0 ;
    clock_t time_head , time_end ;
   
    tck = sysconf (_SC_CLK_TCK );   

    time_head = times ( & time_buf_head );  
    printf ("head_time is : %f \n " , time_head / (double )tck ); 

    //system ("./time_test.exe");
    system ("sleep 2" );   
   
    time_end = times ( & time_buf_end );  
    printf ("end_time is : %f \n " , time_end / (double )tck );

    printf ("user time is : %f \n " , ((time_buf_end . tms_utime - time_buf_head . tms_utime ) / double )tck ));  
    printf ("systime time is : %f \n " , ((time_buf_end . tms_stime - time_buf_head . tms_stime ) / double )tck ));
    printf ("child user time is : %f \n " , ((time_buf_end . tms_cutime - time_buf_head . tms_cutime ) / (double )tck ));
    printf ("child sys time is : %f \n " , ((time_buf_end . tms_cstime - time_buf_head . tms_cstime ) / (double )tck ));
    return (0 );
}

运行输出：

beyes@beyes-groad:~$ ./time.exe
head_time is : 17236892.770000
end_time is : 17236894.790000
user time is : 0.000000
systime time is : 0.000000
child user time is : 0.000000
child sys time is : 0.000000

从上面看到，时间间隔刚好是 2s,下面的时间值都是 0。

为了验证问题，现在修改一下源程序：

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/times.h>

int main ()
{
        struct tms time_buf_head , time_buf_end ;
        long   tck = 0 ;
        clock_t time_head , time_end ;
        int i ;
        int j ;

        tck = sysconf (_SC_CLK_TCK );

        time_head = times ( & time_buf_head );
        printf ("head_time is : %f \n " , time_head / (double )tck );

       
        for (i = 0 ; i < 20000 ; i ++ )
                for (j = 0 ; j < 20000 ; j ++ ) {
                        ;
        }

        time_end = times ( & time_buf_end );
        printf ("end_time is : %f \n " , time_end / (double )tck );

        printf ("user time is : %f \n " , ((time_buf_end . tms_utime - time_buf_head . tms_utime ) / double )tck ));  
        printf ("systime time is : %f \n " , ((time_buf_end . tms_stime - time_buf_head . tms_stime ) / (double )tck ));
        printf ("child user time is : %f \n " , ((time_buf_end . tms_cutime - time_buf_head . tms_cutime ) / (double )tck ));
        printf ("child sys time is : %f \n " , ((time_buf_end . tms_cstime - time_buf_head . tms_cstime ) / (double )tck ));
        return (0 );
}

运行输出：

beyes@beyes-groad:~$ ./time.exe
head_time is : 17184643.070000
end_time is : 17184644.280000
user time is : 1.200000
systime time is : 0.000000
child user time is : 0.000000
child sys time is : 0.000000

    由于使用了大量的延迟，这时可以看到 user time 里耗费了 1.2s ，而 end_time 和 head_time 的时间间隔为 1.21s 约等于 1.2s 。

再来修改一下代码：

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/times.h>

int main ()
{
        struct tms time_buf_head , time_buf_end ;
        long   tck = 0 ;
        clock_t time_head , time_end ;
        int i ;
        int j ;

        tck = sysconf (_SC_CLK_TCK );

        time_head = times ( & time_buf_head );
        printf ("head_time is : %f \n " , time_head / (double )tck );

        for (i = 0 ; i < 1000 ; i ++ )
                for (j = 0 ; j < 1000 ; j ++ ) {
                        open ("Cannon-1.txt" , O_RDONLY );
        }

        time_end = times ( & time_buf_end );
        printf ("end_time is : %f \n " , time_end / (double )tck );

        printf ("user time is : %f \n " , ((time_buf_end . tms_utime - time_buf_head . tms_utime ) / double )tck ));
        printf ("systime time is : %f \n " , ((time_buf_end . tms_stime - time_buf_head . tms_stime ) / (double )tck ));
        printf ("child user time is : %f \n " , ((time_buf_end . tms_cutime - time_buf_head . tms_cutime ) / (double )tck ));
        printf ("child sys time is : %f \n " , ((time_buf_end . tms_cstime - time_buf_head . tms_cstime ) / (double )tck ));
        return (0 );
}

运行输出：

beyes@beyes-groad:~$ ./time.exe
head_time is : 17189923.210000
end_time is : 17189923.650000
user time is : 0.160000
systime time is : 0.280000
child user time is : 0.000000
child sys time is : 0.000000

    在上面的输出中可以看到，systime time 这时不再为 0，这是因为程序中使用了 open() 这个系统调用的结果，它在两个 for 循环里一共被调用了 1000*1000次，总耗时为0.28s ，而执行这两个 for 的时间为 0.16s ，两个时间加起来的时间间隔正好为 end_time - head_time = 0.44s 。

    下面测试子进程的时间，也就是 child user time 和 child sys time 两个。这里，需要另外一个程序，它的主要作用就是和上面一样的调用 open() 打开一个在本目录下的一文本文件，代码如下：

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main ()
{
        int i ;
        int j ;

        for (i = 0 ; i < 1000 ; i ++ )
                for (j = 0 ; j < 1000 ; j ++ ) {
                        open ("Cannon-1.txt" , O_RDONLY );
        }
        return (0 );
}

    上面的程序命名为 time_test.exe ，它会在主程序里被 system() 函数调用到，修改主程序如下：

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/times.h>

int main ()
{
        struct tms time_buf_head , time_buf_end ;
        long   tck = 0 ;
        clock_t time_head , time_end ;
        int i ;
        int j ;

        tck = sysconf (_SC_CLK_TCK );

        time_head = times ( & time_buf_head );
        printf ("head_time is : %f \n " , time_head / (double )tck );

        system ("./time_test.exe" );

        time_end = times ( & time_buf_end );
        printf ("end_time is : %f \n " , time_end / (double )tck );

        printf ("user time is : %f \n " , ((time_buf_end . tms_utime - time_buf_head . tms_utime ) / double )tck ));
        printf ("systime time is : %f \n " , ((time_buf_end . tms_stime - time_buf_head . tms_stime ) / (double )tck ));
        printf ("child user time is : %f \n " , ((time_buf_end . tms_cutime - time_buf_head . tms_cutime ) / (double )tck ));
        printf ("child sys time is : %f \n " , ((time_buf_end . tms_cstime - time_buf_head . tms_cstime ) / (double )tck ));
        return (0 );
}

运行输出：

beyes@beyes-groad:~$ ./time.exe
head_time is : 17190766.590000
end_time is : 17190767.060000
user time is : 0.000000
systime time is : 0.000000
child user time is : 0.140000
child sys time is : 0.300000

    由上可见，child user time 和 child sys time 两者的时间也是为 0.44s，这和上面是一样的，这是因为程序的内容相同。