一文学会C/C++time()和clock()时间函数

曾经终败给现在 2022-10-11 12:28 161阅读 0赞

### C/C++时间函数 ###

*   *  时间函数time()
     *  时钟函数clock()
     *  实例看区别

## 时间函数time() ##

*  **C/C++中的时间函数是`time()`**

time_t time(time_t *__timer) 
    //Return the current time and put it in *TIMER if TIMER is not NULL.

*  **相关的数据类型是`time_t`**
 *  **`time_t` 是长整形数**

typedef long time_t 
     //Returned by `time'.

## 时钟函数clock() ##

*  **C/C++中的计时函数是`clock()`**

clock_t clock(void)

*  **与其相关的数据类型是`clock_t`**
 *  **`clock_t`是一个长整形数**

typedef long clock_t
    //Returned by `clock'.

*  **在`time.h`文件中，还定义了一个常量`CLOCKS_PER_SEC`，它用来表示一秒钟会有多少个时钟计时单元**

#define CLOCKS_PER_SEC ((__clock_t) 1000000)//Linux系统中为1000000

## 实例看区别 ##

# include <stdio.h>
    # include <time.h>
    
    int main(){ 
    
        time_t begin,finish;
        time_t real_begin,real_finish;
        float time_run;
        clock_t start,end;
    
    
        real_begin=time(&begin);//time_t time(time_t *__timer) Return the current time and put it in *TIMER if TIMER is not NULL.
        sleep(10);
        real_finish=time(&finish);
        time_run=difftime(finish,begin);//double difftime(time_t __time1, time_t __time0) Return the difference between TIME1 and TIME0.
        printf("time() start time: %ld\n",real_begin);
        printf("time() finish time: %ld\n",real_finish);
        printf("time() run time: %f\n",time_run);
    
    
        start=clock();//clock_t clock(void)
        sleep(10);
        end=clock();
        printf("clock() start clock tick: %ld\n",start);
        printf("clock() finish clock tick: %ld\n",end);
        printf("clock() run clock ticks: %ld\n",(end-start));
        printf("clock() run time: %ld\n",(end-start)/CLOCKS_PER_SEC);
    
    
        return 0;
    }

运行结果
    time() start time: 1625055012
    time() finish time: 1625055022
    time() run time: 10.000000
    clock() start clock tick: 681
    clock() finish clock tick: 717
    clock() run clock ticks: 36
    clock() run time: 0
    
    //总结
    time()返回从自纪元 Epoch（UTC：1970-01-01 00:00:00）到当前时刻的秒数。
    clock()返回从“开启这个程序进程”到“程序中调用clock()函数”时之间的CPU时钟计时单元（clock tick）数
    所以，用time()计时才是人们正常意识上的秒数，而clock()计时所表示的是占用CPU的时钟单元。