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+<html>
+<head>
+<title>SWIG:Examples:tcl:value</title>
+</head>
+
+<body bgcolor="#ffffff">
+
+
+<tt>SWIG/Examples/tcl/value/</tt>
+<hr>
+
+<H2>Passing and Returning Structures by Value</H2>
+
+<p>
+Occasionally, a C program will manipulate structures by value such as shown in the
+following code:
+
+<blockquote>
+<pre>
+/* File : example.c */
+
+typedef struct Vector {
+   double x, y, z;
+} Vector;
+
+double dot_product(Vector a, Vector b) {
+  return (a.x*b.x + a.y*b.y + a.z*b.z);
+}
+
+Vector vector_add(Vector a, Vector b) {
+  Vector r;
+  r.x = a.x + b.x;
+  r.y = a.y + b.y;
+  r.z = a.z + b.z;
+  return r;
+}
+</pre>
+</blockquote>
+
+Since SWIG only knows how to manage pointers to structures (not their internal
+representation), the following translations are made when wrappers are
+created:
+
+<blockquote>
+<pre>
+double wrap_dot_product(Vector *a, Vector *b) {
+    return dot_product(*a,*b);
+}
+
+Vector *wrap_vector_add(Vector *a, Vector *b) {
+    Vector *r = (Vector *) malloc(sizeof(Vector));
+    *r = vector_add(*a,*b);
+    return r;
+}
+</pre>
+</blockquote>
+
+The functions are then called using pointers from the scripting language interface.
+It should also be noted that any function that returns a structure by value results
+in an implicit memory allocation. This will be a memory leak unless you take steps
+to free the result (see below).
+
+<h2>The SWIG interface</h2>
+
+Click <a href="example.i">here</a> to see a SWIG interface file that
+wraps these two functions.  In this file, there are a few essential features:
+
+<ul>
+<li>A wrapper for the <tt>free()</tt> function is created so that we
+can clean up the return result created by <tt>vector_add()</tt>
+function.
+
+<p>
+<li>The %inline directive is used to create a few helper functions for creating new Vector
+objects and to print out the value (for debugging purposes).
+</ul>
+
+<h2>A Tcl Script</h2>
+
+Click <a href="runme.tcl">here</a> to see a script that uses these functions from Tcl.
+
+<h2>Notes</h2>
+
+<ul>
+<li>When the '<tt>-c++</tt>' option is used, the resulting wrapper code for the return value
+changes to the following:
+
+<blockquote>
+<pre>
+Vector *wrap_vector_add(Vector *a, Vector *b) {
+    Vector *r = new Vector(vector_add(*a,*b));
+    return r;
+}
+</pre>
+</blockquote>
+
+Similarly, it would be a mistake to use the <tt>free()</tt> function from C++.  A safer 
+approach would be to write a helper function like this:
+
+<blockquote>
+<pre>
+%inline %{
+   void delete_Vector(Vector *v) {
+       delete v;
+   }
+%}
+</pre>
+</blockquote>
+
+<p>
+<li>Passing parameters by value like this really isn't the best C programming style.
+If possible, you might change your application to use pointers.
+
+<p>
+<li>Similar translations are made when C++ references are used.
+
+
+</ul>
+
+<hr>
+</body>
+</html>