Editing Struct (C programming language) (section)

{{Short description|C keyword for defining a structured data type}}
{{lowercase}}
In the [[C programming language]], '''struct''' is the keyword used to define a [[composite data type|composite]], a.k.a. [[Record (computer science)|record]], [[data type]] {{endash}} a named set of values that occupy a block of memory. It allows for the different values to be accessed via a single [[identifier]], often a [[pointer (computer programming)|pointer]]. A struct can contain other data types so is used for mixed-data-type records. For example a bank customer struct might contains fields: name, address, telephone, balance.

A struct occupies a ''contiguous block'' of memory, usually delimited (sized) by word-length boundaries. It corresponds to the similarly named feature available in some [[assembly language|assemblers]] for Intel processors. Being a block of contiguous memory, each field within a struct is located at a certain fixed offset from the start.

The [[sizeof]] operator results in the number of bytes needed to store a particular struct, just as it does for a [[primitive data type]]. The alignment of particular fields in the struct (with respect to [[Word (computer architecture)|word]] boundaries) is implementation-specific and may include padding. Modern compilers typically support the <code>#pragma pack</code> directive, which sets the size in bytes for alignment.<ref>{{Cite web|url=https://stackoverflow.com/questions/2748995/struct-memory-layout-in-c|title=Struct memory layout in C|website=Stack Overflow}}</ref>

The C struct feature was derived from the same-named concept in [[ALGOL 68]].<ref name="sigplan">{{cite journal | first = Dennis M.| last = Ritchie | authorlink = Dennis Ritchie | title = The Development of the C Language | date = March 1993 | journal = ACM SIGPLAN Notices | volume = 28 | issue = 3 | pages = 201–208 | url = http://www.bell-labs.com/usr/dmr/www/chist.html | doi = 10.1145/155360.155580 | quote = The scheme of type composition adopted by C owes considerable debt to Algol 68, although it did not, perhaps, emerge in a form that Algol's adherents would approve of. The central notion I captured from Algol was a type structure based on atomic types (including structures), composed into arrays, pointers (references), and functions (procedures). Algol 68's concept of unions and casts also had an influence that appeared later.| doi-access = free }}</ref>