Field (computer science)

<h2 id="memory-fields">Memory fields</h2>
Fields may be stored in <a href="/facts/Random_access_memory/DuD4bxh6">random access memory</a> (RAM). The following <a href="/facts/Pascal_(programming_language)/b3yvp8bF">Pascal</a> record definition has three field identifiers: firstName, lastName, and age. The two name fields have a datatype of an <a href="/facts/Array_(data_structure)/BKGvF8AM">array</a> of <a href="/facts/Character_(computing)/X2zKLFFB">character</a>. The age field has a datatype of <a href="/facts/Integer/PUwwrawx">integer</a>.

type PersonRecord =
 record
 lastName : array [ 1 .. 20 ] of Char;
 firstName : array [ 1 .. 20 ] of Char;
 age : Integer
 end;

In Pascal, the identifier component precedes a colon, and the datatype component follows the colon. Once a record is defined, <a href="/facts/Instance_variable/UQXdtMBp">variables</a> of the record can be <a href="/facts/Instance_(computer_science)/5zPBGdX1">allocated</a>. Once the memory of the record is allocated, a field can be accessed like a variable by using the dot notation.

var alice : PersonRecord;
alice.firstName := 'Alice';

The term field has been replaced with the terms data member<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> and attribute.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> The following <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a> <a href="/facts/Class_(computer_programming)/zvzkSAtE">class</a> has three attributes: firstName, lastName, and age.

public class PersonRecord
{
	private String firstName;
	private String lastName;
	private int age;
}

<h2 id="file-fields">File fields</h2>

Fields may be stored in a <a href="/facts/Random_access/1cxrCk3r">random access</a> <a href="/facts/Computer_file/FjFH3Ufm">file</a>.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> A file may be written to or read from in an arbitrary order. To accomplish the arbitrary access, the <a href="/facts/Operating_system/8XTuvMh2">operating system</a> provides a method to quickly seek around the file.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> Once the <a href="/facts/Disk_read-and-write_head/WdpxUpjK">disk head</a> is positioned at the beginning of a record, each file field can be read into its corresponding memory field.
File fields are the main storage structure in the <a href="/facts/ISAM/J1Q7sty3">Indexed Sequential Access Method</a> (ISAM). In <a href="/facts/Relational_database/pEKGmJLy">relational database</a> <a href="/facts/Database_theory/unyQa3cK">theory</a>, the term field has been replaced with the terms column and attribute.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Class_variable/H5b1PUyR">Class variable</a> – Variable defined in a class whose objects all possess the same copy</li>
<li><a href="/facts/Mutator_method/sKfxYzFM">Mutator method</a> – Computer science method</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Jensen, Kathleen; Wirth, Niklaus (1974). PASCAL User Manual and Report. Springer-Verlag. p. 42. ISBN 0-387-90144-2. [A] record is a structure consisting of a fixed number of components, called fields. <a href="0-387-90144-2" target="_blank">0-387-90144-2</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Wilson, Leslie B.; Clark, Robert G. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 169. ISBN 0-201-71012-9. Being able to structure data in this way is central to the construction of understandable programs. <a href="0-201-71012-9" target="_blank">0-201-71012-9</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Wilson, Leslie B.; Clark, Robert G. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 169. ISBN 0-201-71012-9. <a href="0-201-71012-9" target="_blank">0-201-71012-9</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Jensen, Kathleen; Wirth, Niklaus (1974). PASCAL User Manual and Report. Springer-Verlag. p. 42. ISBN 0-387-90144-2. <a href="0-387-90144-2" target="_blank">0-387-90144-2</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Stroustrup, Bjarne (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley. p. 450. ISBN 978-0-321-56384-2. <a href="978-0-321-56384-2" target="_blank">978-0-321-56384-2</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Wilson, Leslie B.; Clark, Robert G. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 104. ISBN 0-201-71012-9. <a href="0-201-71012-9" target="_blank">0-201-71012-9</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Wilson, Leslie B.; Clark, Robert G. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 169. ISBN 0-201-71012-9. The original use of records was in languages like COBOL, where they were used to define the structure of records held in a file. <a href="0-201-71012-9" target="_blank">0-201-71012-9</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Kernighan, Brian W.; Pike, Rob (1984). The UNIX Programming Environment. Prentice Hall. p. 207. ISBN 0-13-937699-2. The system call lseek provides a way to move around in a file without actually reading or writing. <a href="0-13-937699-2" target="_blank">0-13-937699-2</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Date, C.J. (2005). Database in Depth. O'Reilly Media, Inc. p. 5. ISBN 0-596-10012-4. An n-ary relation can be pictured as a table with n columns; the columns in the picture correspond to attributes of the relation and the rows correspond to tuples. <a href="0-596-10012-4" target="_blank">0-596-10012-4</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
</ol>

Field (computer science) open-in-new

Field (computer science)