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<title>CLASS keyword</title>
<!-- Changed by: Martin Leslie, 14-Mar-1996 -->
<body bgcolor=#dddddd>
<font color=brown>
<hr>
<center><h1>class keyword</h1></center>
<hr>
<p>
The concept of a class
allows you to
<a href=../../C/glossary.html#encapsulation>encapsulate</a>
a set of related variables and only
allow access to them via predetermined functions.
<p>
The <b>class</b> keyword is used to declare the group of variables
and functions and the visability of the variables and functions.
Here is a basic example.
<p>
<center>
<table width="80%" border="1" bgcolor="ivory">
<tr>
<td>
<pre>
class String
{
public:
void Set(char *InputStr) // Declare an Access function
{
strcpy(Str, InputStr);
}
private:
char Str[80]; // Declare a hidden variable.
};
</pre>
</td>
</tr>
</table>
</center>
<p>
<ul>
<li><b>private:</b> means that all variables and functions that
follow are only visable from within the class.
<li><b>public:</b> all functions and variables that follow this
statement can be accessed from outside the class.
</ul>
Now we have declared a class called <b>String</b> we need to
use it.
<p>
<center>
<table width="80%" border="1" bgcolor="ivory">
<tr>
<td>
<pre>
main()
{
String Title;
Title.Set("My First Masterpiece.");
}
</pre>
</td>
</tr>
</table>
</center>
<p>
This code creates a String
<a href=../../C/glossary.html#class_object>object</a>
called Title and then uses the <b>Set</b> member function
to initialise the value of <b>Str</b>.
<p>
In C++ the member function <b>Set</b> is also known as a
<a href=../../C/glossary.html#method>method</a>
<p>
This is the strength
of object oriented programming, the ONLY way to change
<b>Str</b> is via the <b>Set</b> method.
<p>
The final code example brings the last two examples together
ands a new method (called Get) that shows the contents of
<b>Str</b>
<p>
<center>
<table width="80%" border="1" bgcolor="ivory">
<tr>
<td>
<pre>
#include <stdlib.h>
#include <iostream.h> // Instead of stdio.h
class String
{
public:
void Set(char *InputStr) // Declare an Access function
{
strcpy(Str, InputStr);
}
<b>
char *Get(void) // Declare an Access function
{
return(Str);
}
</b>
private:
char Str[80]; // Declare a hidden variable.
};
main()
{
String Title;
Title.Set("My First Masterpiece.");
<b>cout << Title.Get() << endl;</b>
}
</pre>
</td>
</tr>
</table>
</center>
<p>
<hr>
<h2>Examples:</h2>
<img src="../../GRAPHICS/computer.gif">
<a href="../EXAMPLES/class1.cc">Example program.</a>
<hr>
<h2>See Also:</h2>
<img src="../../GRAPHICS/whiteball.gif">
<a href="../CONCEPT/constructor.html">Constructors and destructors.</a>
<p>
<img src="../../GRAPHICS/whiteball.gif">
<a href="../CONCEPT/inheritance.html">Class Inheritance.</a>
<hr>
</font>
<font color=black>
<h2>C References</h2>
<p>
<hr>
<p>
<center>
<table border=2 width=80% bgcolor="ivory">
<tr align=center>
<td width="25%">
<a href="../cref.html">Top</a>
</td><td width="25%">
<a href="../../C/master_index.html">Master Index</a>
</td><td width="25%">
<a href="keywords.html">C++ Keywords</a>
</td><td width="25%">
<a href="../../C/FUNCTIONS/funcref.htm">Functions</a>
</td>
</tr>
</table>
</center>
<p>
<hr>
<font color=brown>
<address>Martin Leslie
08-Feb-96</address><p>
</font>
|
