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| |
| <h3 class="section">9.4 Searching and Sorting Example</h3> |
| |
| <p>Here is an example showing the use of <code>qsort</code> and <code>bsearch</code> |
| with an array of structures. The objects in the array are sorted |
| by comparing their <code>name</code> fields with the <code>strcmp</code> function. |
| Then, we can look up individual objects based on their names. |
| |
| <!-- This example is dedicated to the memory of Jim Henson. RIP. --> |
| <pre class="smallexample"> #include <stdlib.h> |
| #include <stdio.h> |
| #include <string.h> |
| |
| /* <span class="roman">Define an array of critters to sort.</span> */ |
| |
| struct critter |
| { |
| const char *name; |
| const char *species; |
| }; |
| |
| struct critter muppets[] = |
| { |
| {"Kermit", "frog"}, |
| {"Piggy", "pig"}, |
| {"Gonzo", "whatever"}, |
| {"Fozzie", "bear"}, |
| {"Sam", "eagle"}, |
| {"Robin", "frog"}, |
| {"Animal", "animal"}, |
| {"Camilla", "chicken"}, |
| {"Sweetums", "monster"}, |
| {"Dr. Strangepork", "pig"}, |
| {"Link Hogthrob", "pig"}, |
| {"Zoot", "human"}, |
| {"Dr. Bunsen Honeydew", "human"}, |
| {"Beaker", "human"}, |
| {"Swedish Chef", "human"} |
| }; |
| |
| int count = sizeof (muppets) / sizeof (struct critter); |
| |
| |
| |
| /* <span class="roman">This is the comparison function used for sorting and searching.</span> */ |
| |
| int |
| critter_cmp (const struct critter *c1, const struct critter *c2) |
| { |
| return strcmp (c1->name, c2->name); |
| } |
| |
| |
| /* <span class="roman">Print information about a critter.</span> */ |
| |
| void |
| print_critter (const struct critter *c) |
| { |
| printf ("%s, the %s\n", c->name, c->species); |
| } |
| |
| |
| /* <span class="roman">Do the lookup into the sorted array.</span> */ |
| |
| void |
| find_critter (const char *name) |
| { |
| struct critter target, *result; |
| target.name = name; |
| result = bsearch (&target, muppets, count, sizeof (struct critter), |
| critter_cmp); |
| if (result) |
| print_critter (result); |
| else |
| printf ("Couldn't find %s.\n", name); |
| } |
| |
| /* <span class="roman">Main program.</span> */ |
| |
| int |
| main (void) |
| { |
| int i; |
| |
| for (i = 0; i < count; i++) |
| print_critter (&muppets[i]); |
| printf ("\n"); |
| |
| qsort (muppets, count, sizeof (struct critter), critter_cmp); |
| |
| for (i = 0; i < count; i++) |
| print_critter (&muppets[i]); |
| printf ("\n"); |
| |
| find_critter ("Kermit"); |
| find_critter ("Gonzo"); |
| find_critter ("Janice"); |
| |
| return 0; |
| } |
| </pre> |
| <p><a name="index-Kermit-the-frog-834"></a>The output from this program looks like: |
| |
| <pre class="smallexample"> Kermit, the frog |
| Piggy, the pig |
| Gonzo, the whatever |
| Fozzie, the bear |
| Sam, the eagle |
| Robin, the frog |
| Animal, the animal |
| Camilla, the chicken |
| Sweetums, the monster |
| Dr. Strangepork, the pig |
| Link Hogthrob, the pig |
| Zoot, the human |
| Dr. Bunsen Honeydew, the human |
| Beaker, the human |
| Swedish Chef, the human |
| |
| Animal, the animal |
| Beaker, the human |
| Camilla, the chicken |
| Dr. Bunsen Honeydew, the human |
| Dr. Strangepork, the pig |
| Fozzie, the bear |
| Gonzo, the whatever |
| Kermit, the frog |
| Link Hogthrob, the pig |
| Piggy, the pig |
| Robin, the frog |
| Sam, the eagle |
| Swedish Chef, the human |
| Sweetums, the monster |
| Zoot, the human |
| |
| Kermit, the frog |
| Gonzo, the whatever |
| Couldn't find Janice. |
| </pre> |
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