c++计时

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本文介绍如何在Linux环境下利用clock_gettime()函数实现精确到纳秒级别的程序计时，通过不同类型的计时器（如CLOCK_REALTIME、CLOCK_PROCESS_CPUTIME_ID和CLOCK_THREAD_CPUTIME_ID）进行计时，并提供了一个示例程序来展示如何获取并计算两个时间点之间的差值。

Linux下使用clock_gettime给程序计时

哦，clock_gettime( ) 提供了纳秒的精确度，给程序计时可是不错哦；

      
        
      
      
        
      
      
       
       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：
       
       
         
       
       
         
       
       
        代码
       
       
        1 struct timespec {2  time_t tv_sec; /* seconds */3  long tv_nsec; /* nanoseconds */4 };
       
       
         
       
       
         
       
       
         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 }