1. #include <stdio.h>
2. #include <stdlib.h>
3. #include <errno.h>
4. #include <string.h>
5. /** Our old friend die from ex17. */
6. void die(const char *message)
7. {
8.  if(errno) {
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15.  if(errno) {
16.  perror(message);
17.  } else {
18.  printf("ERROR: %sn", message);
19.  }
20.  exit(1);
21. }
22. // a typedef creates a fake type, in this
23. // case for a function pointer
24. typedef int (*compare_cb)(int a, int b);
25. /**
26.  * A classic bubble sort function that uses the
27.  * compare_cb to do the sorting.
28.  */
29. int *bubble_sort(int *numbers, int count, compare_cb cmp)
30. {
31.  int temp = 0;
32.  int i = 0;
33.  int j = 0;
34.  int *target = malloc(count * sizeof(int));
35.  if(!target) die("Memory error.");
36.  memcpy(target, numbers, count * sizeof(int));
37.  for(i = 0; i < count; i++) {
38.  for(j = 0; j < count - 1; j++) {
39.  if(cmp(target[j], target[j+1]) > 0) {
40.  temp = target[j+1];
41.  target[j+1] = target[j];
42.  target[j] = temp;
43.  }
44.  }
45.  }
46.  return target;
47. }
48. int sorted_order(int a, int b)
49. {
50.  return a - b;
51. }
52. int reverse_order(int a, int b)
53. {
54.  return b - a;
55. }
56. int strange_order(int a, int b)
57. {
58.  if(a == 0 || b == 0) {
59.  return 0;
60.  } else {
61.  return a % b;
62.  }
63. }
64. /**
65.  * Used to test that we are sorting things correctly
66.  * by doing the sort and printing it out.
67.  */
68. void test_sorting(int *numbers, int count, compare_cb cmp)
69. {
70.  int i = 0;
71.  int *sorted = bubble_sort(numbers, count, cmp);
72.  if(!sorted) die("Failed to sort as requested.");
73.  for(i = 0; i < count; i++) {
74.  printf("%d ", sorted[i]);
75.  }
76.  printf("n");
77.  free(sorted);
78. }
79. int main(int argc, char *argv[])
80. {
81.  if(argc < 2) die("USAGE: ex18 4 3 1 5 6");
82.  int count = argc - 1;
83.  int i = 0;
84.  char **inputs = argv + 1;
85.  int *numbers = malloc(count * sizeof(int));
86.  if(!numbers) die("Memory error.");
87.  for(i = 0; i < count; i++) {
88.  numbers[i] = atoi(inputs[i]);
89.  }
90.  test_sorting(numbers, count, sorted_order);
91.  test_sorting(numbers, count, reverse_order);
92.  test_sorting(numbers, count, strange_order);
93.  free(numbers);
94.  return 0;
95. }
96.