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<html><head><title>XLISP aref</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
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<hr>
<h1>aref</h1>
<hr>
<p><table cellpadding="0" cellspacing="0" style="margin-left:10px"><tbody>
<tr valign="top">
<td><nobr>Type:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>function (subr)</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>xlbfun.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<p><div class="box">
<dl>
<dt>(<b>aref</b> <i>array element</i>)</dt>
<dd><i>array</i> - an array expression<br>
<i>element</i> - an integer expression<br>
returns - the value of the array element</dd>
</dl>
</div></p>
<h2>Description</h2>
<p>The 'aref' function returns the specified element out of a previously
created array. Array elements may be any valid lisp data type, including
lists or arrays. Arrays made by <a href="make-array.htm">make-array</a> and
accessed by 'aref' are <nobr>base 0</nobr>. This means the first element is
accessed by element <nobr>number '0'</nobr> and the last element is accessed
by element <nobr>number 'n-1'</nobr> [where 'n' is the array size]. Array
elements are initialized to <a href="nil.htm">NIL</a>.</p>
<h2>Examples</h2>
<pre class="example">
(setq my-array '#(0 1 2 3 4)) => #(0 1 2 3 4)
(aref my-array 0) => 0
(aref my-array 4) => 4
(aref my-array 5) => <font color="#AA0000">error: array index out of bounds - 5</font>
my-array => #(0 1 2 3 4)
(setq new (make-array 4)) => #(NIL NIL NIL NIL)
(setf (aref new 0) (make-array 4)) => #(NIL NIL NIL NIL)
new => #(#(NIL NIL NIL NIL) NIL NIL NIL)
(setf (aref (aref new 0) 1) 'a) => A
new => #(#(NIL A NIL NIL) NIL NIL NIL)
(setf (aref new 2) '(a b c)) => (A B C)
new => #(#(NIL A NIL NIL) NIL (A B C) NIL)
</pre>
<p><b>Read macro:</b> There is a built-in read-macro for arrays,
<nobr>'#(...)'</nobr> <nobr>[the hash</nobr> symbol with the array elements
in parentheses]. This allows you to create arbitrary arrays with initial
values without going through a <a href="make-array.htm">make-array</a>
function. See the <a href="../manual/xlisp.htm#the-readtable">Readtable</a>
section in the <nobr>XLISP 2.0</nobr> Manual.</p>
<p><b>Note:</b> This function returns the value of an array element.
However, there is no equivalent direct function to set the value of an array
element to some value. <nobr>To set</nobr> an element value, you must use
the <a href="setf.htm">setf</a> function.
<nobr>The <a href="setf.htm">setf</a></nobr> function is a generalized
function that allows you to set the value of arbitrary lisp entities.</p>
<p>See also:</p>
<ul>
<li><nobr>Contents → <a href="../manual/contents.htm#array-functions">Array Functions</a></nobr></li>
</ul>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
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