34c97ffdbd
Fix numerous inaccuracies in index.html (where it exists) and eliminate unnecessary differences between the example code being wrapped.
242 lines
4.6 KiB
HTML
242 lines
4.6 KiB
HTML
<html>
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<head>
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<title>SWIG:Examples:tcl:class</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/tcl/class/</tt>
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<hr>
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<H2>Wrapping a simple C++ class</H2>
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<p>
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This example illustrates the most primitive form of C++ class wrapping performed
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by SWIG. In this case, C++ classes are simply transformed into a collection of
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C-style functions that provide access to class members.
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<h2>The C++ Code</h2>
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Suppose you have some C++ classes described by the following (and admittedly lame)
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header file:
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<blockquote>
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<pre>
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/* File : example.h */
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class Shape {
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public:
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Shape() {
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nshapes++;
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}
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virtual ~Shape() {
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nshapes--;
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}
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double x, y;
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void move(double dx, double dy);
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virtual double area() = 0;
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virtual double perimeter() = 0;
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static int nshapes;
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};
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class Circle : public Shape {
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private:
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double radius;
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public:
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Circle(double r) : radius(r) { }
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virtual double area();
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virtual double perimeter();
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};
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class Square : public Shape {
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private:
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double width;
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public:
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Square(double w) : width(w) { }
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virtual double area();
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virtual double perimeter();
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};
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</pre>
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</blockquote>
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<h2>The SWIG interface</h2>
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A simple SWIG interface for this can be built by simply grabbing the header file
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like this:
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<blockquote>
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<pre>
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/* File : example.i */
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%module example
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%{
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#include "example.h"
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%}
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/* Let's just grab the original header file here */
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%include "example.h"
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</pre>
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</blockquote>
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Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this:
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<blockquote>
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<pre>
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% swig -c++ -tcl example.i
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</pre>
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</blockquote>
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<h2>Some sample Tcl scripts</h2>
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SWIG performs two forms of C++ wrapping-- a low level interface and a high level widget-like interface.
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<ul>
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<li>
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Click <a href="runme.tcl">here</a> to see a script that calls the C++ functions using the
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low-level interface.
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<li>
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Click <a href="runme2.tcl">here</a> to see the same script written with the high-level
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interface.
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</ul>
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<h2>Key points</h2>
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<ul>
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<li>The low-level C++ interface works like this:
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<p>
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<ul>
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<li>To create a new object, you call a constructor like this:
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<blockquote>
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<pre>
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set c [new_Circle 10.0]
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</pre>
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</blockquote>
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<p>
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<li>To access member data, a pair of accessor functions are used.
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For example:
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<blockquote>
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<pre>
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Shape_x_set $c 15 ;# Set member data
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set x [Shape_x_get $c] ;# Get member data
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</pre>
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</blockquote>
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Note: when accessing member data, the name of the base class must
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be used such as <tt>Shape_x_get</tt>
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<p>
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<li>To invoke a member function, you simply do this
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<blockquote>
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<pre>
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puts "The area is [Shape_area $c]"
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</pre>
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</blockquote>
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<p>
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<li>Type checking knows about the inheritance structure of C++. For example:
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<blockquote>
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<pre>
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Shape_area $c # Works (c is a Shape)
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Circle_area $c # Works (c is a Circle)
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Square_area $c # Fails (c is definitely not a Square)
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</pre>
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</blockquote>
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<p>
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<li>To invoke a destructor, simply do this
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<blockquote>
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<pre>
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delete_Shape $c # Deletes a shape
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</pre>
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</blockquote>
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<p>
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<li>Static member variables are wrapped as C global variables. For example:
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<blockquote>
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<pre>
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set n $Shape_nshapes # Get a static data member
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set Shapes_nshapes 13 # Set a static data member
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</pre>
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</blockquote>
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</ul>
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<p>
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<li>The high-level interface works like a Tk widget
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<p>
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<ul>
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<li>To create a new object, you call a constructor like this:
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<blockquote>
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<pre>
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Circle c 10 # c becomes a name for the Circle object
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</pre>
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</blockquote>
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<p>
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<li>To access member data, use cget and configure methods.
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For example:
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<blockquote>
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<pre>
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c configure -x 15 ;# Set member data
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set x [c cget -x] ;# Get member data
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</pre>
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</blockquote>
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<p>
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<li>To invoke a member function, you simply do this
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<blockquote>
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<pre>
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puts "The area is [c area]"
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</pre>
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</blockquote>
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<p>
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<li>To invoke a destructor, simply destroy the object name like this:
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<blockquote>
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<pre>
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rename c "" # c goes away
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</pre>
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</blockquote>
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<p>
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<li>Static member variables are wrapped as C global variables. For example:
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<blockquote>
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<pre>
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set n $Shape_nshapes # Get a static data member
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set Shapes_nshapes 13 # Set a static data member
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</pre>
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</blockquote>
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</ul>
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</ul>
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<h2>General Comments</h2>
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<ul>
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<li>The low-level function interface is much faster than the high-level interface.
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In fact, all the higher level interface does is call functions in the low-level interface.
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<li>SWIG *does* know how to properly perform upcasting of objects in an inheritance
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hierarchy (including multiple inheritance). Therefore it is perfectly safe to pass
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an object of a derived class to any function involving a base class.
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<li>C++ Namespaces - %nspace isn't yet supported for Python.
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</ul>
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<hr>
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</body>
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</html>
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