1 files changed, 76 insertions, 0 deletions
diff --git a/Examples/tcl/variables/index.html b/Examples/tcl/variables/index.html
new file mode 100644
index 0000000..245a445
--- /dev/null
+++ b/Examples/tcl/variables/index.html
@@ -0,0 +1,76 @@
+<html>
+<head>
+<title>SWIG:Examples:tcl:variables</title>
+</head>
+
+<body bgcolor="#ffffff">
+
+<tt>SWIG/Examples/tcl/variables/</tt>
+<hr>
+
+<H2>Wrapping C Global Variables</H2>
+
+<p>
+When a C global variable appears in an interface file, SWIG tries to wrap it using a technique
+known as "variable linking."  The idea is pretty simple---we try to create a Tcl
+variable that works exactly like you would expect in a Tcl script, but which magically 
+retrieves or updates the value of the underlying C variable.  
+Click <a href="example.i">here</a> to see a SWIG interface with some variable declarations in it.
+
+<h2>Manipulating Variables from Tcl</h2>
+
+Click <a href="runme.tcl">here</a> to see a script that updates and prints out the values of
+the variables defined in the above file.  Notice how the C global variables work just
+like normal Tcl variables.
+
+<h2>Key points</h2>
+
+<ul>
+<li>The <tt>set</tt> statement changes the value of the corresponding C global variable.
+<li>Whenever you access the value of a variable such as <tt>$ivar</tt>, the value
+of the C global variable is read. 
+<li>If a C program changes a global variable independently of Tcl, this change is
+automatically reflected in the Tcl variable (i.e., reads will always return the
+most up to date value of the variable).
+<li>When a global variable has the type "<tt>char *</tt>", SWIG manages it as a character
+string.   However, whenever the value of such a variable is set from Tcl, the old
+value is destroyed using <tt>free()</tt> or <tt>delete</tt> (the choice of which depends
+on whether or not SWIG was run with the -c++ option).
+<li><tt>signed char</tt> and <tt>unsigned char</tt> are handled as small 8-bit integers.
+<li>String array variables such as '<tt>char name[256]</tt>' are managed as Tcl strings, but
+when setting the value, the result is truncated to the maximum length of the array.  Furthermore, the string is assumed to be null-terminated.
+<li>When structures and classes are used as global variables, they are mapped into pointers.
+Getting the "value" returns a pointer to the global variable.  Setting the value of a structure results in a memory copy from a pointer to the global.
+</ul>
+
+<h2>Creating read-only variables</h2>
+
+The <tt>%immutable</tt> and <tt>%mutable</tt> directives can be used to
+specify a collection of read-only variables.  For example:
+
+<blockquote>
+<pre>
+%immutable;
+int    status;
+double blah;
+...
+%mutable;
+</pre>
+</blockquote>
+
+The <tt>%immutable</tt> directive remains in effect until it is explicitly disabled
+using the <tt>%mutable</tt> directive.
+
+<h2>Comments</h2>
+<ul>
+<li>Management of global variables is one of the most problematic aspects 
+of C/C++ wrapping because the scripting interface and resulting memory management
+is much trickier than simply creating a wrapper function.
+<p>
+<li>You may be better off hiding global variables behind a function based
+interface.
+</ul>
+
+</body>
+</html>
+<hr>