Programming Tutorials

Using the qsort() and bsearch() functions with values - example program in C

By: Manoj Kumar in C Tutorials on 2007-10-03  

This program lets you enter up to MAX values (20 in this case). It sorts the values and prints them in order. Then it lets you enter a value to search for in the array. A printed message states the search's status.

Familiar code is used to obtain the values for the array on lines 18 and 19. Line 26 contains the call to qsort() to sort the array. The first argument is a pointer to the array's first element. This is followed by MAX, the number of elements in the array. The size of the first element is then provided so that qsort() knows the width of each item. The call is finished with the argument for the sort function, intcmp.

The function intcmp() is defined on lines 52 through 55. It returns the difference of the two values passed to it. This might seem too simple at first, but remember what values the comparison function is supposed to return. If the elements are equal, 0 should be returned. If element one is greater than element two, a positive number should be returned. If element one is less than element two, a negative number should be returned. This is exactly what intcmp() does.

The searching is done with bsearch(). Notice that its arguments are virtually the same as those of qsort(). The difference is that the first argument of bsearch() is the key to be searched for. bsearch() returns a pointer to the location of the found key or NULL if the key isn't found. On line 43, ptr is assigned the returned value of bsearch(). ptr is used in the if loop on lines 45 through 48 to print the status of the search.

1: /* Using qsort() and bsearch() with values.*/
2:
3: #include <stdio.h>
4: #include <stdlib.h>
5:
6: #define MAX 20
7:
8: int intcmp(const void *v1, const void *v2);
9:
10: main()
11: {
12:      int arr[MAX], count, key, *ptr;
13:
14:      /* Enter some integers from the user. */
15:
16:      printf("Enter %d integer values; press Enter after each.\n", MAX);
17:
18:      for (count = 0; count < MAX; count++)
19:          scanf("%d", &arr[count]);
20:
21:      puts("Press Enter to sort the values.");
22:      getc(stdin);
23:
24:      /* Sort the array into ascending order. */
25:
26:      qsort(arr, MAX, sizeof(arr[0]), intcmp);
27:
28:      /* Display the sorted array. */
29:
30:      for (count = 0; count < MAX; count++)
31:          printf("\narr[%d] = %d.", count, arr[count]);
32:
33:      puts("\nPress Enter to continue.");
34:      getc(stdin);
35:
36:      /* Enter a search key. */
37:
38:      printf("Enter a value to search for: ");
39:      scanf("%d", &key);
40:
41:      /* Perform the search. */
42:
43:      ptr = (int *)bsearch(&key, arr, MAX, sizeof(arr[0]),intcmp);
44:
45:      if ( ptr != NULL )
46:          printf("%d found at arr[%d].", key, (ptr - arr));
47:      else
48:          printf("%d not found.", key);
49:      return(0);
50: }
51:
52: int intcmp(const void *v1, const void *v2)
53: {
54:      return (*(int *)v1 - *(int *)v2);
55: }
Enter 20 integer values; press Enter after each.
45
12
999
1000
321
123
2300
954
1968
12
2
1999
1776
1812
1456
1
9999
3
76
200
Press Enter to sort the values.
arr[0] = 1.
arr[1] = 2.
arr[2] = 3.
arr[3] = 12.
arr[4] = 12.
arr[5] = 45.
arr[6] = 76.
arr[7] = 123.
arr[8] = 200.
arr[9] = 321.
arr[10] = 954.
arr[11] = 999.
arr[12] = 1000.
arr[13] = 1456.
arr[14] = 1776.
arr[15] = 1812.
arr[16] = 1968.
arr[17] = 1999.
arr[18] = 2300.
arr[19] = 9999.
Press Enter to continue.
Enter a value to search for:
1776
1776 found at arr[14]