c - 我的C程序中的输出有问题(给出了意外的输出)

Question

该程序有什么问题，应该计算每个函数调用的运行时间，但是令我惊讶的是，运行时间始终为零，因为begin和end完全相同。有人对此有解释吗？
这是我得到的输出:

TIMING TEST: 10000000 calls to rand()

   2113   6249  23817  12054   7060   9945  26819
  13831   6820  14149  13035  30858  13924  26467
   4268  11314  28400   5239   4496  27757  21452
  10878  25064   9049   6508  29612  11373  29913
  10234  31769  16167  24553   1875  23992  30606
   2606  19539   2184  14832  27089  27474  23310
, .. , ,

End time: 1610034404
Begin time: 1610034404
Elapsed time: 0
Time for each call:,10f

这是代码:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define NCALLS 10000000
#define NCOLS  7
#define NLINES 7

int main(void) {
    int i, val;
    long begin, diff, end;

    begin = time(NULL);
    srand(time(NULL));
    printf("\nTIMING TEST: %d calls to rand()\n\n", NCALLS);
    for (i = 1; i <= NCALLS; ++i) {
        val = rand();
        if (i <= NCOLS * NLINES) {
            printf("%7d", val);
            if (i % NCOLS == 0)
                putchar('\n');
        } else
        if (i == NCOLS * NLINES + 1)
            printf("%7s\n\n", ", .. , ,");
    }
    end = time(NULL);
    diff = end - begin;
    printf("%s%ld\n%s%ld\n%s%ld\n%s%,10f\n\n",
           "End time: ", end,
           "Begin time: ", begin,
           "Elapsed time: ", diff,
           "Time for each call:", (double)diff / NCALLS);
    return 0;
}

Answer 1

可以使用time(NULL)代替clock()

time_t t1 = clock();

// your code

time_t t2 = clock();

printf("%f", (double)(t2 - t1) / CLOCKS_PER_SEC); // you have to divide it to CLOCKS_PER_SEC (1 000 000) if you want time in seconds

time()以秒为单位进行度量，因此，如果您的程序不花1秒钟，您将不会看到差异
stackoverflow中的某个人已经回答了它们之间的区别 time() vs clock()