下面是一个非常简单的方法：枚举n-1和1之间的所有整数，并打印严格包含在n中的整数，即：(i & n) == i .

void list_descendants(int n) {
    printf("descendants of %d:", n);
    for (int i = n; i --> 1;) {
        if ((i & n) == i)
            printf(" %d", i);
    }
    printf("\n");
}

好吧，我终于想出了一个C代码，它看起来一点也不好看，可能优化得很糟糕，但仍然能按预期工作。可能有更简单的解决方案，但这里是我的知识目的：

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
unsigned int pui(unsigned int a, unsigned int b)
{
  if (b == 0)
    return 1;
  if (b == 1)
    return a;
  if (b % 2 == 0)
    return pui(a * a, b / 2);
  else
    return pui(a * a, (b - 1) / 2);
}
unsigned int testBit(unsigned int h, unsigned int offset)
{
  unsigned int mask = 1 << offset;
  return (h & mask);
}

bool isInList(unsigned int x, unsigned int *output_size, unsigned int **output)
{
  for (int i = 0; i < *output_size; i++)
  {
    if (*(*output + i) == x)
    {
      return true;
    }
  }
  return false;
}
void listDescendants(unsigned int h, unsigned int *output_size, unsigned int **output, int *currently_processing)
{
  unsigned int max_offset = 0;
  unsigned int temp_h = h;
  unsigned int initial_output_size = *output_size;
  while (temp_h > 0)
  {
    max_offset++;
    temp_h /= 2;
  }
  unsigned int h_radix2[max_offset];
  for (int i = 0; i < max_offset; i++)
  {
    if (testBit(h, i))
    {

      if (h > pui(2, i) && !isInList(h - pui(2, i), output_size, output))
      {
        *(*output + *output_size) = h - pui(2, i);
        *output_size += 1;
      }
    }
  }

  if (*currently_processing < (int)*output_size)
  {
    *currently_processing += 1;
    listDescendants(*(*output + *currently_processing), output_size, output, currently_processing);
  }
}

int main()
{
  
  int currently_processing = -1;
  unsigned int size = 0;
  unsigned int *output = malloc(300 * sizeof(unsigned int));
  listDescendants(21, &size, &output, &currently_processing);

  printf("size = %u\n", size);
  for (int i = 0; i < size; i++)
  {
    printf("%u ", output[i]);
  }
  printf("\n");

  return 0;
}

您可以使用递归解决方案，如下所示。
我有点懒，所以我没有把数字列成一个列表，而是简单地打印出来，我还打印了0和给定的数字。
我相信你可以很容易地调整代码，使它能做你想做的事情。

#include <stdio.h>

#define CHAR_BIT 8

void ProperDescendantsRecursive(unsigned int num, unsigned int bit_index)
{
    if (CHAR_BIT * sizeof(unsigned int) - 1 == bit_index)
    {
        printf("%u\n", num);
    }
    else
    {
        unsigned int mask = 1U << bit_index;
        if (num & mask)
        {
            /* with the bit at index bit_index is off */
            ProperDescendantsRecursive(num ^ mask, bit_index + 1);
            /* with the bit at index bit_index is on */
            ProperDescendantsRecursive(num, bit_index + 1);
        }
        else
        {
            ProperDescendantsRecursive(num, bit_index + 1);
        }
    }
}

void ProperDescendants(unsigned int num)
{
    ProperDescendantsRecursive(num, 0);
}

int main(void)
{
    ProperDescendants(21);
    
    return 0;
}

编译和运行结果此输出：

0
16
4
20
1
17
5
21