{"id":948,"date":"2014-09-13T00:01:21","date_gmt":"2014-09-13T07:01:21","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=948"},"modified":"2014-09-20T08:39:49","modified_gmt":"2014-09-20T15:39:49","slug":"breaking-down-structures","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=948","title":{"rendered":"Breaking Down Structures"},"content":{"rendered":"

In the C language, struct<\/code> is a variable type, but do you declare<\/em> a structure or define<\/em> a structure? That one has me perplexed.
\n
\nRegardless of the nomenclature, a structure is a collection of variable types, like a record in a database. You can pack any type of variable into a structure — including more structures. The idea is that the information within the structure is related and somehow serves a useful purpose by being referenced as a unit.<\/p>\n

A simple example is a structure that holds a date value:<\/p>\n

struct date {\r\n    int year;\r\n    int month;\r\n    int day;\r\n};<\/code><\/pre>\n
The structure is named date<\/code>. It holds three members (not elements), all int<\/em> variables.<\/p>\n
Defining a structure doesn’t create a structure variable. It merely tells the compiler, “Hey! Here’s a new type of structure. Maybe I’ll use it.” To declare a structure variable, you use this format:<\/p>\n
struct date birthday;<\/code><\/p>\n
The variable birthday<\/code> uses the date<\/code> structure type. It’s assumed that the date<\/code> structure is defined elsewhere.<\/p>\n
Here’s sample code:<\/p>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n    struct date {\r\n        int year;\r\n        int month;\r\n        int day;\r\n    };\r\n    struct date birthday;\r\n\r\n    birthday.year = 1935;\r\n    birthday.month = 7;\r\n    birthday.day = 6;\r\n\r\n    printf(\"The Dalai Lama was born on %d\/%02d\/%d.\\n\",\r\n            birthday.month,\r\n            birthday.day,\r\n            birthday.year);\r\n\r\n    return(0);\r\n}<\/pre>\n
To access a structures members, you use the structure variable name (not the structure name). So the sample code uses birthday<\/code> not date<\/code>. Then you use a dot and the structure member name.<\/p>\n
Here’s sample output:<\/p>\n
The Dalai Lama was born on 7\/06\/1935.<\/code><\/pre>\n
Hopefully all this info is familiar to you if you’ve read my books. If not, it always helps to brush up.<\/p>\n
One thing other programmers do that I don’t is combine the structure definition and the variable declaration into a single statement. It looks like this:<\/p>\n
struct date {\r\n    int year;\r\n    int month;\r\n    int day;\r\n} birthday;<\/code><\/pre>\n
This statement (it’s one statement split over 5 lines) both defines the date<\/code> structure and declares a date<\/code> structure variable, birthday<\/code>. You may prefer this method, which is fine. I expand it out to two statements, which does the same thing but it makes structures easier to teach.<\/p>\n
For me, the most difficult part of using structures is coming up with clever names: one for the structure itself and another for the structure variable. Generally speaking, I can come up with a single clever name for either the structure or the variable, but not both. I’ll continue to work on that.<\/p>\n
In next week’s Lesson<\/a>, I’ll review nested structures.<\/p>\n","protected":false},"excerpt":{"rendered":"
Fear not the struct<\/code> variable. It can be fun and useful. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-948","post","type-post","status-publish","format-standard","hentry","category-main"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/948","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=948"}],"version-history":[{"count":4,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/948\/revisions"}],"predecessor-version":[{"id":998,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/948\/revisions\/998"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=948"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=948"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=948"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}