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authorTobias Klauser <tklauser@distanz.ch>2008-01-27 11:37:44 +0100
committerTobias Klauser <tklauser@xenon.tklauser.home>2008-01-27 11:37:44 +0100
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+<html>
+<head>
+<title>Reference variables</title>
+</head>
+<body bgcolor="#dddddd">
+<font color=brown>
+<hr>
+<center><h1>Reference Variables.</h1></center>
+<hr>
+<p>
+Reference variables allow two variable names to address the
+same memory location. The following example shows the
+technique in its simplest form.
+
+<p>
+<center>
+<table border=1 width="80%" bgcolor="ivory">
+<tr>
+<td>
+<pre>
+
+ #include <iostream.h>
+
+ main()
+ {
+ int var1;
+ int &var2 = var1; // var2 is a reference variable.
+
+ var1 = 10;
+
+ cout << "var1 = " << var1 << endl;
+ cout << "var2 = " << var2 << endl;
+ }
+</pre>
+</td>
+</tr>
+</table>
+</center>
+<p>
+
+
+Generally, you would not use a reference variable
+in this way. Its more likely that they would be used
+in function parameter lists to make the passing of
+pointers more readable.
+<p>
+This gives C++ the ability to provide a
+different approch to changing a variable from within a
+function. Consider the two following programs.
+
+<p>
+<center>
+<table border=1 width="80%" bgcolor="ivory">
+<tr>
+
+<td>
+<pre>
+
+ #include &lt;stdio.h&gt;
+
+ void Square(<b>int *pVal</b>);
+
+ main()
+ {
+ int Number=10;
+
+ printf("Number is %d\n", Number);
+
+ Square(<b>&Number</b>);
+
+ printf("Number is %d\n", Number);
+ }
+
+ void Square(<b>int *pVal</b>)
+ {
+ <b>*pVal</b> *= <b>*pVal;</b>
+
+ printf("Number is %d\n", <b>*pVal</b>);
+ }
+
+</pre>
+</td>
+<td>
+<pre>
+
+ #include &lt;stdio.h&gt;
+
+ void Square(<b>int &Val</b>);
+
+ main()
+ {
+ int Number=10;
+
+ printf("Number is %d\n", Number);
+
+ Square(<b>Number</b>);
+
+ printf("Number is %d\n", Number);
+ }
+
+ void Square(<b>int &Val</b>)
+ {
+ <b>Val</b> *= <b>Val</b>;
+
+ printf("Number is %d\n", <b>Val</b>);
+ }
+
+</pre>
+</td>
+</tr>
+</table>
+</center>
+<p>
+
+The program on the right should be clearer to read
+because you do not need to worry about pointer
+dereferencing.
+
+<hr>
+<h2>Examples:</h2>
+<img src="../../GRAPHICS/computer.gif" alt="o">
+<a href="..//EXAMPLES/refvar.cc">Example program.</a>
+<p>
+
+<font color=brown>
+<img src="../../GRAPHICS/computer.gif" alt="o">
+<a href="../../C/EXAMPLES/pointer_func.c">Example C program.</a>
+</font>
+
+<hr>
+<h2>See Also:</h2>
+
+</font>
+<hr>
+<font color=black>
+<h2>C References</h2>
+<p>
+<img src="../../GRAPHICS/whiteball.gif" alt="o">
+<a href="../../C/CONCEPT/data_types.html">data types</a>.
+
+</font>
+
+<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="../SYNTAX/keywords.html">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
+29-Sep-96</address><p>
+</font>
+</body>
+</html>