有时我们需要评价一个算法性能，那么算法的执行时间便是一个不可忽视的因素，而由于某种特殊的需求，我们需要算法的执行时间尽可能地精确，linux下就提供了这样的一个函数：clock_gettime。该函数提供的可是提供了纳秒的精确度。
函数的原型如下：
int clock_gettime(clockid_t clk_id, struct timespect *tp);
clockid_t clk_id用于指定计时时钟的类型，对于我们Programmr以下三种比较常用：
CLOCK_REALTIME, a system-wide realtime clock.
CLOCK_PROCESS_CPUTIME_ID, high-resolution timer provided by the CPU for each process.
CLOCK_THREAD_CPUTIME_ID, high-resolution timer provided by the CPU for each of the threads.
CLOCK_REALTIME, a system-wide realtime clock.
CLOCK_PROCESS_CPUTIME_ID, high-resolution timer provided by the CPU for each process.
CLOCK_THREAD_CPUTIME_ID, high-resolution timer provided by the CPU for each of the threads.
struct timespect *tp用来存储当前的时间，其结构如下：
1 struct timespec {
2 time_t tv_sec; /* seconds */
3 long tv_nsec; /* nanoseconds */
4 };
#include <stdio.h>
#include <time.h>
struct timespec diff(struct timespec start,struct timespec end)
{
struct timespec temp;
if((end.tv_nsec-start.tv_nsec)<0)
{
temp.tv_sec = end.tv_sec-start.tv_sec-1;
temp.tv_nsec = 1000000000 + end.tv_nsec-start.tv_nsec;
}
else
{
temp.tv_sec = end.tv_sec-start.tv_sec;
temp.tv_nsec = end.tv_nsec-start.tv_nsec;
}
return temp;
}
int main()
{
struct timespec time1,time2,temp;
int i;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time1);
for(i=0; i<10000;i++)
{
;
}
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time2);
temp = diff(time1, time2);
printf("%d:%d\n", temp.tv_sec, temp.tv_nsec);
return 0;
}
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这里需要注意一点的就是，编译时需要链接lrt库，否则会提示找不到clock_gettime函数，
[root@localhost ~]# gcc timetest.c -o timetest -lrt