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Class implementation file

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In <a href="Object-oriented_programming" title="Object-oriented programming">object-oriented programming</a>, a class implementation file is often used to contain the implementation code for the <a href="Method_(computer_programming)" title="Method (computer programming)">method(s)</a> of a <a href="Class_(computer_programming)" title="Class (computer programming)">class</a>. Programming languages like C++ and Objective-C make use of these implementation files so as to separate the interface and implementation of these methods.<a href="#cite_note-1">[1]</a>

<div class="mw-heading mw-heading2"><h2 id="Motivation">Motivation</h2></div>

Using this structure, a <a href="Class_definition" class="mw-redirect" title="Class definition">class definition</a> file containing the declaration of the class and its members is also created. If the class definition has been included and the implementation file for its methods is available, the user can <a href="Instance_(computer_science)" title="Instance (computer science)">instantiate</a> an <a href="Object_(computer_science)" title="Object (computer science)">object</a> of the class. The purpose of this structure is to keep the implementation code hidden, but allow the user to view the design.<a href="#cite_note-2">[2]</a><a href="#cite_note-3">[3]</a>

Users make use of the public interface of an <a href="Object_(computer_science)" title="Object (computer science)">object</a> so as to make creating objects as simple as possible, ensuring that client code does not distract the user with unnecessary details of the class's implementation.<a href="#cite_note-4">[4]</a>

This allows the user the information needed to use the class effectively, but prevents him or her from damaging the compiled code.<a href="#cite_note-5">[5]</a>

<div class="mw-heading mw-heading2"><h2 id="The_structure_of_a_class_implementation_file">The structure of a class implementation file</h2></div>

An implementation file is used in <a href="The_C%2B%2B_Programming_Language" title="The C++ Programming Language">C++ programming</a> when creating a <a href="Class_definition" class="mw-redirect" title="Class definition">class definition</a> to split the interface from the implementation. The <a href="Header_file" class="mw-redirect" title="Header file">header file</a> would declare all the <a href="C%2B%2B_classes" title="C++ classes">member functions</a> (methods) and <a href="C%2B%2B_classes" title="C++ classes">data methods</a> (fields) that the class has.<a href="#cite_note-6">[6]</a><a href="#cite_note-7">[7]</a><a href="#cite_note-8">[8]</a>

The implementation file will contain the actual definition or <a href="Source_code" title="Source code">source code</a> of the methods declared in the <a href="Header_file" class="mw-redirect" title="Header file">header file</a>. This file can start with a header block, which provides comments that describe the purpose of the defined class and any details about the creation of the actual file, such as the author of the file and date the file was created.<a href="#cite_note-9">[9]</a>

It can also include any libraries from the <a href="C%2B%2B_Standard_Library" title="C++ Standard Library">C++ Standard Library</a> that will be used by any of the declared methods in the file. The class implementation file will usually have a line to include the associated header file (see examples below).

<div class="mw-heading mw-heading3"><h3 id="Example_in_C++">Example in C++</h3></div>

An example would be having a class called <code>ExampleClass</code>. The header file of this C++ file would be named "example_class.h" and the implementation file would be "example_class.cc".<a href="#cite_note-10">[10]</a><a href="#cite_note-11">[11]</a>

An example of the structure of example_class.cc would look like this:

<div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>#include "example_class.h"

ExampleClass::ExampleClass() = default;

void ExampleClass::AddSomething(int k) {

...

}

</pre></div>

In this example, the implementation for the functions has been omitted, but the functions must be declared in example_class.h like this:<a href="#cite_note-12">[12]</a>

<div class="mw-highlight mw-highlight-lang-cpp mw-content-ltr" dir="ltr"><pre>#include <string>

class ExampleClass {

public:

ExampleClass(); // Constructor.

void AddSomething(int k);

private:

std::string name_;

};

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="Example_in_Objective-C">Example in Objective-C</h3></div>

Another example of how a class implementation file would be structured can be seen with <a href="Objective-C" title="Objective-C">Objective-C</a>, which is used in <a href="IOS" title="IOS">iOS</a> programming.<a href="#cite_note-13">[13]</a>

This example will use "ExampleClass". A notable difference between C++ and <a href="Objective-C" title="Objective-C">Objective-C</a> when making use of these implementation files is the extensions used at the end of the files. In C++ it will be .cpp<a href="#cite_note-14">[14]</a>

and in <a href="Objective-C" title="Objective-C">Objective-C</a> it will be .m,<a href="#cite_note-15">[15]</a>

but both will use the same .h extension for their <a href="Header_file" class="mw-redirect" title="Header file"> header file(s)</a><a href="#cite_note-16">[16]</a><a href="#cite_note-17">[17]</a>

as shown in the example below.

This is an example of ExampleClass.h in <a href="Objective-C" title="Objective-C">Objective-C</a>:

<div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>#import <UIKit/UIKit.h>

@interface ExampleClass : NSObject {

// instance variable declarations go here

}

- (NSString*) name;

@end

</pre></div>

This is an example of the class's implementation file Exampleclass.m in <a href="Objective-C" title="Objective-C">Objective-C</a>:

<div class="mw-highlight mw-highlight-lang-objc mw-content-ltr" dir="ltr"><pre>#import "ExampleClass.h"

@implementation ExampleClass

- (NSString*) name {

return @"…";

}

@end

</pre></div>

<ul><li><a href="C%2B%2B_classes" title="C++ classes">C++ classes</a></li>

<li><a href="Header_file" class="mw-redirect" title="Header file">Header file</a></li>

<li><a href="Source_code" title="Source code">Source code</a></li>

<li><a href="C%2B%2B_Standard_Library" title="C++ Standard Library">C++ Standard Library</a></li>

<li><a href="Objective-C" title="Objective-C">Objective-C</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFAlan_Griffiths2005" class="citation web cs1">Alan Griffiths (2005). <a rel="nofollow" class="external text" href="http://accu.org/index.php/journals/269">"Separating Interface and Implementation in C++"</a>. ACCU. Retrieved 2013-05-07.</cite>

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<cite id="CITEREFAlan_Griffiths2005" class="citation web cs1">Alan Griffiths (2005). <a rel="nofollow" class="external text" href="http://accu.org/index.php/journals/269">"Separating Interface and Implementation in C++"</a>. ACCU. Retrieved 2013-05-07.</cite>

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<cite id="CITEREFNeuberg2011" class="citation book cs1">Neuberg, Matt (26 May 2011). "Chapter 4.3 Header File and Implementation File". <a rel="nofollow" class="external text" href="https://archive.org/details/programmingios40000neub">Programming iOS 4</a>. O'Reilly Media, Inc. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-4493-8843-0</bdi>.</cite>

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<cite id="CITEREFAlan_Griffiths2005" class="citation web cs1">Alan Griffiths (2005). <a rel="nofollow" class="external text" href="http://accu.org/index.php/journals/269">"Separating Interface and Implementation in C++"</a>. ACCU. Retrieved 2013-05-07.</cite>

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<cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.chromium.org/developers/coding-style/cpp-dos-and-donts">"C++ Dos and Don'ts"</a>. The Chromium Projects. Retrieved 2013-05-07.</cite>

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<cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://pages.cs.wisc.edu/~hasti/cs368/CppTutorial/NOTES/CLASSES-INTRO.html">"Introduction to C++ Classes"</a>. Retrieved 2013-05-07.</cite>

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<cite id="CITEREFAlan_Griffiths2005" class="citation web cs1">Alan Griffiths (2005). <a rel="nofollow" class="external text" href="http://accu.org/index.php/journals/269">"Separating Interface and Implementation in C++"</a>. ACCU. Retrieved 2013-05-07.</cite>

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<cite id="CITEREFFebil_Chacko_Thanikal2009" class="citation web cs1">Febil Chacko Thanikal (2009). <a rel="nofollow" class="external text" href="http://www.codeproject.com/Articles/48575/How-to-define-a-template-class-in-a-h-file-and-imp">"How to define a template class in a .h file and implement it in a .cpp file"</a>. Code Project. Retrieved 2013-05-07.</cite>

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<cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.itechtalk.com/thread1517.html">"The implementation file in C++ Programming"</a>. ITechTalk. Retrieved 2013-05-07.</cite>

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<cite id="CITEREFNeuberg2011" class="citation book cs1">Neuberg, Matt (26 May 2011). "Chapter 4.3 Header File and Implementation File". <a rel="nofollow" class="external text" href="https://archive.org/details/programmingios40000neub">Programming iOS 4</a>. O'Reilly Media, Inc. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-4493-8843-0</bdi>.</cite>

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<cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://pages.cs.wisc.edu/~hasti/cs368/CppTutorial/NOTES/CLASSES-INTRO.html">"Introduction to C++ Classes"</a>. Retrieved 2013-05-07.</cite>

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<cite id="CITEREFNeuberg2011" class="citation book cs1">Neuberg, Matt (26 May 2011). "Chapter 4.3 Header File and Implementation File". <a rel="nofollow" class="external text" href="https://archive.org/details/programmingios40000neub">Programming iOS 4</a>. O'Reilly Media, Inc. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-4493-8843-0</bdi>.</cite>

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<cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://pages.cs.wisc.edu/~hasti/cs368/CppTutorial/NOTES/CLASSES-INTRO.html">"Introduction to C++ Classes"</a>. Retrieved 2013-05-07.</cite>

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<cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://pages.cs.wisc.edu/~hasti/cs368/CppTutorial/NOTES/CLASSES-INTRO.html">"Introduction to C++ Classes"</a>. Retrieved 2013-05-07.</cite>

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<cite id="CITEREFNeuberg2011" class="citation book cs1">Neuberg, Matt (26 May 2011). "Chapter 4.3 Header File and Implementation File". <a rel="nofollow" class="external text" href="https://archive.org/details/programmingios40000neub">Programming iOS 4</a>. O'Reilly Media, Inc. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-1-4493-8843-0</bdi>.</cite>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://my.safaribooksonline.com/book/programming/iphone/9781449397302/objective-c-classes/_header_file_and_implementation_file">Header File and Implementation File</a></li></ul></div><div><div class="zim-footer">

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