Linux 下使用clock_gettime给程序计时详解

下使用clock_gettime给程序计时详解，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:系统实时时间,随系统实时时间改变而改变,即从UTC1970-1-1 0:0:0开始计时,中间时刻如果系统时间被用户该成其他,则对应的时间相应改变
        CLOCK_MONOTONIC:从系统启动这一刻起开始计时,不受系统时间被用户改变的影响
        CLOCK_PROCESS_CPUTIME_ID:本进程到当前代码系统CPU花费的时间
        CLOCK_THREAD_CPUTIME_ID:本线程到当前代码系统CPU花费的时间

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 };

下面我们就上代码把；

代码

1 #include <iostream>
2 #include <time.h>
3  using namespace std;
4
5 timespec diff(timespec start, timespec end);
6
7  int main()
8 {
9 timespec time1, time2;
10 int temp;
11 clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time1);
12 for (int i = 0; i< 242000000; i++)
13 temp+=temp;
14 clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &time2);
15 cout<<diff(time1,time2).tv_sec<<":"<<diff(time1,time2).tv_nsec<<endl;
16 return 0;
17 }
18
19 timespec diff(timespec start, timespec end)
20 {
21 timespec temp;
22 if ((end.tv_nsec-start.tv_nsec)<0) {
23 temp.tv_sec = end.tv_sec-start.tv_sec-1;
24 temp.tv_nsec = 1000000000+end.tv_nsec-start.tv_nsec;
25 } else {
26 temp.tv_sec = end.tv_sec-start.tv_sec;
27 temp.tv_nsec = end.tv_nsec-start.tv_nsec;
28 }
29 return temp;
30 }