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<html><head><title>XLISP peek-char</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
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<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>peek-char</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>xlfio.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<dl>
<dt>(peek-char [<i>skip-flag</i> [<i>source</i>]])</dt>
<dd><i>skip-flag</i> - an optional expression, default is
<a href="nil.htm">NIL</a><br>
<i>source</i> - an optional source, must be a file pointer or stream, default
is <a href="global-standard-input.htm">*standard-input*</a><br>
returns - the character</dd>
</dl>
<h2>Description</h2>
<p>The 'peek-char' function looks at a single character from the specified
'source'. The character looked-at is returned as an integer value for the
result. If the 'skip-flag' expression is
<nobr><a href="nil.htm">NIL</a> ,</nobr> then the next character
will be looked-at, without advancing the position within the file. If the
'skip-flag' expression is <nobr>non-<a href="nil.htm">NIL</a>
,</nobr> then the next non-white-space character will be looked-at. This
skipping does advance the position within the file. White-space characters
include 'blank', 'tab' and 'new-line' characters. If 'skip-flag' is not
used, no skipping will occur. The 'source' may be a file pointer or a
stream. If there is no 'source',
<a href="global-standard-input.htm">*standard-input*</a> is the default. If an
end-of-file is encountered in the 'source', then
<a href="nil.htm">NIL</a> will be returned as the result.</p>
<h2>Examples</h2>
<pre class="example">
(setq fp (open "f" :direction :output)) <font color="#008844">; create file "f"</font>
(print 12 fp)
(princ " 34" fp)
(terpri fp)
(close fp)
(setq fp (open "f" :direction :input)) <font color="#008844">; open "f" for reading</font>
(peek-char NIL fp) <font color="#008844">; returns #\1</font>
(peek-char NIL fp) <font color="#008844">; returns #\1 - didn't advance</font>
(read-char fp) <font color="#008844">; returns #\1 - force advance</font>
(peek-char NIL fp) <font color="#008844">; returns #\2</font>
(read-char fp) <font color="#008844">; returns #\2 - force advance</font>
(peek-char NIL fp) <font color="#008844">; returns #\Newline</font>
(peek-char T fp) <font color="#008844">; returns #\3 - skipped blanks</font>
(read-line fp) <font color="#008844">; returns "34"</font>
(close fp)
</pre>
<p><b>Common Lisp:</b> The XLISP and Common Lisp 'peek-char' functions are
compatible for simple cases. They both allow for the optional 'skip-flag'
and 'source'. However, in Common Lisp, there are additional parameters which
occur right after 'source' that support various end-of-file operations and
recursive calls. So, when porting from Common Lisp to XLISP, remember there
are additional arguments in Common Lisp's 'peek-char' that are not supported
in XLISP.</p>
<p>See the
<a href="../manual/xlisp-man-029.htm#peek-char">peek-char</a>
function in the <nobr>XLISP 2.0</nobr> manual.</p>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
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