c - time.h 库不工作

Question

我正在学习 K&R 书和练习 3-1。我认为我的“time.h”库坏了。起初我以为我的代码是错误的，但是当我检查练习的解决方案时在网络上，它们也不起作用。

问题:

程序输出始终显示零秒，并且“时钟”有时会交换:

Output 1:
    Element -1 not found.
    binsearch() took 10000 clocks (0 seconds)
    Element -1 not found.
    binsearch2() took 20000 clocks (0 seconds)

Output 2:
    Element -1 not found.
    binsearch() took 20000 clocks (0 seconds)
    Element -1 not found.
    binsearch2() took 10000 clocks (0 seconds)

该程序的目的是比较两个函数的速度。我该如何比较？

这是测试代码:

 for ( i = 0, time_taken = clock(); i < 100000; ++i ) {
    index = binsearch(n, testdata, MAX_ELEMENT);   /* all this code is duplicated with a
}                                                     call to binsearch2 instead */
time_taken = clock() - time_taken;

if ( index < 0 )
    printf("Element %d not found.\n", n);
else
    printf("Element %d found at index %d.\n", n, index);

printf("binsearch() took %lu clocks (%lu seconds)\n",
       (unsigned long) time_taken,
       (unsigned long) time_taken / CLOCKS_PER_SEC);

我在 Linux 和 Windows 中都尝试过这个程序。

Answer 1

您的系统中可能有CLOCKS_PER_SEC=1000000。

因此，time_taken/CLOCKS_PER_SEC 给出了预期的 0。

将代码更改为 double(time_taken)/CLOCKS_PER_SEC 以获取浮点。