{"id":5660,"date":"2022-12-08T00:01:46","date_gmt":"2022-12-08T08:01:46","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=5660"},"modified":"2022-12-03T11:43:37","modified_gmt":"2022-12-03T19:43:37","slug":"quick-sorting-structures-solution","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=5660","title":{"rendered":"Quick Sorting Structures – Solution"},"content":{"rendered":"

The task for this month’s Exercise<\/a> is to extract a structure member from a void<\/em> pointer for use in the quick-sort compare()<\/em> function. This isn’t a solution you can readily find on the Interwebs.
\n
\nI must have hammered away at various solutions for hours when originally confronted with this problem. I tried every possible combination of asterisk\/parentheses weirdo expression I could muster. Eventually, stepping away from the keyboard — and avoiding the temptation to drink heavily — yielded a clean solution.<\/p>\n

The first thing you must realize is that it’s weirdly complicated to construct a single return<\/em> statement to handle the job. Rather than keep trying, I decided to first convert the void<\/em> pointers into compatible structures. Here is the format:<\/p>\n

one = *(struct film *)a;<\/code><\/p>\n

Variable one<\/code> is a film<\/em> structure. It’s assigned to the passed pointer *a<\/code>, first argument in the compare()<\/em> function, which must be typecast to a film<\/em> structure pointer. Once this conversion is made, struct<\/em> variable one<\/code> is available for comparing the year<\/code> member values, as shown in my full solution here:<\/p>\n

2022_12-Exercise.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n\r\nstruct film {\r\n    char title[32];\r\n    int year;\r\n};\r\n\r\nint compare(const void *a, const void *b)\r\n{\r\n    struct film one,two;\r\n\r\n    one = *(struct film *)a;\r\n    two = *(struct film *)b;\r\n\r\n    return( one.year - two.year );\r\n}\r\n\r\nint main()\r\n{\r\n    const int size = 9;\r\n    struct film bond[size] = {\r\n        { \"Casino Royale\", 2006 },\r\n        { \"Dr. No\", 1962 },\r\n        { \"GoldenEye\", 1995 },\r\n        { \"Goldfinger\", 1964 },\r\n        { \"Moonraker\", 1979 },\r\n        { \"Octopussy\", 1983 },\r\n        { \"Skyfall\", 2012 },\r\n        { \"Spectre\", 2015 },\r\n        { \"Thunderball\", 1965 }\r\n    };\r\n    int x;\r\n\r\n    \/* sort the list by year *\/<\/span>\r\n    qsort(bond,size,sizeof(struct film),compare);\r\n\r\n    \/* output results *\/<\/span>\r\n    for( x=0; x<size; x++ )\r\n        printf(\"%d, %s\\n\",\r\n                bond[x].year,\r\n                bond[x].title\r\n              );\r\n\r\n    return(0);\r\n}<\/pre>\n
Even when I tried to compress the two statements in the compare()<\/em> function, eliminating variables one<\/code> and two<\/code> and setting the conversions into the return<\/em> statement, the program refused to compile. Only by declaring two film<\/em> structures, converting the data in two statements, and then comparing the year<\/code> members, did my solution work.<\/p>\n
It would thrill me to see another solution, something that uses a different approach. As I wrote in the original Exercise post, most programmers tend to copy-paste their compare()<\/em> functions. Yet power exists in this function, part of the quick-sort process. Let me know if you also met with success.<\/p>\n","protected":false},"excerpt":{"rendered":"
The task for this month’s Exercise is to extract a structure member from a void pointer for use in the quick-sort compare() function. This isn’t a solution you can readily find on the Interwebs.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-5660","post","type-post","status-publish","format-standard","hentry","category-solution"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5660","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5660"}],"version-history":[{"count":4,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5660\/revisions"}],"predecessor-version":[{"id":5677,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5660\/revisions\/5677"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5660"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5660"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5660"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}