make a specific variable immutable, supply a declaration name.  For example:
</p>

<div class="code">
<pre>
%{
extern char *path;
%}
%immutable path;
...
extern char *path;      // Read-only (due to %immutable)
</pre>
</div>

<H3><a name="Tcl_nn18">37.3.4 Constants and enums</a></H3>


<p>
C/C++ constants are installed as global Tcl variables containing the
appropriate value.  To create a constant, use <tt>#define</tt>, <tt>enum</tt>, or the
<tt>%constant</tt> directive.  For example:
</p>

<div class="code