Redundant code: Difference between revisions

Revision as of 13:27, 26 March 2011

Latest revision as of 19:10, 27 August 2025

(37 intermediate revisions by 28 users not shown)

Line 1:

In [[computer programming]], '''redundant code''' is [[source code]] or compiled code that is unnecessary. Code that can be removed without affecting its desired behavior is redundant.

{{TOC right}}

==Categories==

{{Unreferenced section|date=October 2008}}

Noteble categoreis of redundant code include:

'''Redundant; code''' is a [[computer programming]] term for code, which may be [[source code]] or compiled code in a [[computer program]], that has any form of redundancy, such asRecomputing: recomputingRecomputing a value that has previously been calculated<ref>[http://doi.acm.org/10.1145/349214.349233 Debray, S. K., Evans, W., Muth, R., and De Sutter, B. 2000. Compiler techniques for code compaction. ACM Trans. Program. Lang. Syst. 22, 2 (Mar. 2000), 378–415.]</ref> and is still available, code that is never executed (often called [[unreachable code]]), or code which is executed but has no external effect (e.g., does not change the output produced by a program), usually known as [[dead code]].

; [[Dead code]]: Code that is executed but has no external effect; e.g., does not change the output produced by a program.

A [[NOP]] instruction might be considered to be redundant code that has been explicitly inserted to pad out the [[instruction (computer science)|instruction]] stream or introduce a time delay. [[Identifier]]s that are declared but never referenced are usually termed as [[redundant declaration]]s.

; [[Unreachable code]]: Code that is never executed. Also, called dead code.

==Example==

<source lang="c">

int f (int x)

{

int y=x*2;

return x*2;

}

</source>

; [[NOP (code)|NOP]] padding: A NOP instruction might be considered redundant if it's for padding. But if the NOP is required for proper functionality then it's not redundant.

The second <tt>x*2</tt> expression is redundant code and can be replaced by a reference to the variable <tt>y</tt>. Alternatively, the definition <tt>int y=x*2</tt> can instead be removed.

; Unused [[identifier]]: Declared, but never referenced is a redundant declaration.

==Examples==

In the following [[C (computer language)|C]] code, the second <code>x * 2</code> expression is redundant code. Line 2 can be removed, or alternatively, line 3 can be changed to {{code| return y;}}.

<syntaxhighlight lang="C" line>

int f foo(int x) {

int y = x * 2;

return x * 2;

}

</syntaxhighlight>

A more subtle example involves the C preprocessor that inserts code before compilation. Consider:

<syntaxhighlight lang="C">

#define min(A,B) ((A)<(B)?(A):(B))

int shorter_magnitude(int a, int b, int c, int d) {

return sqrt(min(a*a + b*b, c*c + d*d));

}

</syntaxhighlight>

After preprocessing, the code expands to code that evaluates both {{code|a*a + b*b}} and {{code|c*c + d*d}} twice. To eliminate the duplicate code, the macro {{code|min}} could ge converted to a function.

<syntaxhighlight lang="C">

int shorter_magnitude(int a, int b, int c, int d) {

return sqrt(((a*a + b*b)<(c*c + d*d)?(a*a + b*b):(c*c + d*d)));

}

</syntaxhighlight>

==See also==

* {{Annotated link |Code bloat}}

{{Portal|Computer Science}}

* {{Annotated link |Code reuse}}

*[[Code bloat]]

* {{Annotated link |Common subexpression elimination}}

* {{Annotated link |Don't repeat yourself}}

* {{Annotated link |Duplicate code}}

* {{Annotated link |Redundancy (information theory)}}

* {{Annotated link |Code refactoring}}

* {{Annotated link |Code smell}}

==References==

Line 26 ⟶ 55:

[[Category:Compiler optimizations]]

[[Category:Software engineering terminologyanomalies]]

[[Category:Source code]]

[[it:Codice ridondante]]

[[lt:Perteklinis kodas]]

[[nl:Redundante code]]