/tags/Root-branch-php-utl/SWIG/Examples/python/class/index.html
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- <title>SWIG:Examples:python:class</title>
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- <tt>SWIG/Examples/python/class/</tt>
- <hr>
- <H2>Wrapping a simple C++ class</H2>
- <tt>$Header$</tt><br>
- <p>
- This example illustrates the most primitive form of C++ class wrapping performed
- by SWIG. In this case, C++ classes are simply transformed into a collection of
- C-style functions that provide access to class members.
- <h2>The C++ Code</h2>
- Suppose you have some C++ classes described by the following (and admittedly lame)
- header file:
- <blockquote>
- <pre>
- /* File : example.h */
- class Shape {
- public:
- Shape() {
- nshapes++;
- }
- virtual ~Shape() {
- nshapes--;
- };
- double x, y;
- void move(double dx, double dy);
- virtual double area() = 0;
- virtual double perimeter() = 0;
- static int nshapes;
- };
- class Circle : public Shape {
- private:
- double radius;
- public:
- Circle(double r) : radius(r) { };
- virtual double area();
- virtual double perimeter();
- };
- class Square : public Shape {
- private:
- double width;
- public:
- Square(double w) : width(w) { };
- virtual double area();
- virtual double perimeter();
- };
- </pre>
- </blockquote>
- <h2>The SWIG interface</h2>
- A simple SWIG interface for this can be built by simply grabbing the header file
- like this:
- <blockquote>
- <pre>
- /* File : example.i */
- %module example
- %{
- #include "example.h"
- %}
- /* Let's just grab the original header file here */
- %include "example.h"
- </pre>
- </blockquote>
- Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this:
- <blockquote>
- <pre>
- % swig -c++ -python example.i
- </pre>
- </blockquote>
- <h2>A sample Python script</h2>
- Click <a href="example.py">here</a> to see a script that calls the C++ functions from Python.
- <h2>Key points</h2>
- <ul>
- <li>To create a new object, you call a constructor like this:
- <blockquote>
- <pre>
- c = example.new_Circle(10.0)
- </pre>
- </blockquote>
- <p>
- <li>To access member data, a pair of accessor functions are used.
- For example:
- <blockquote>
- <pre>
- example.Shape_x_set(c,15) # Set member data
- x = example.Shape_x_get(c) # Get member data
- </pre>
- </blockquote>
- Note: when accessing member data, the name of the class in which
- the member data was must be used. In this case, <tt>Shape_x_get()</tt>
- and <tt>Shape_x_set()</tt> are used since 'x' was defined in Shape.
- <p>
- <li>To invoke a member function, you simply do this
- <blockquote>
- <pre>
- print "The area is ", example.Shape_area(c)
- </pre>
- </blockquote>
- <p>
- <li>Type checking knows about the inheritance structure of C++. For example:
- <blockquote>
- <pre>
- example.Shape_area(c) # Works (c is a Shape)
- example.Circle_area(c) # Works (c is a Circle)
- example.Square_area(c) # Fails (c is definitely not a Square)
- </pre>
- </blockquote>
- <p>
- <li>To invoke a destructor, simply do this
- <blockquote>
- <pre>
- example.delete_Shape(c) # Deletes a shape
- </pre>
- </blockquote>
- (Note: destructors are currently not inherited. This might change later).
- <p>
- <li>Static member variables are wrapped as C global variables. For example:
- <blockquote>
- <pre>
- n = example.cvar.Shape_nshapes # Get a static data member
- example.cvar.Shapes_nshapes = 13 # Set a static data member
- </pre>
- </blockquote>
- </ul>
- <h2>General Comments</h2>
- <ul>
- <li>This low-level interface is not the only way to handle C++ code.
- Shadow classes provide a much higher-level interface.
- <p>
- <li>SWIG *does* know how to properly perform upcasting of objects in
- an inheritance hierarchy (including multiple inheritance). Therefore
- it is perfectly safe to pass an object of a derived class to any
- function involving a base class.
- <p>
- <li>A wide variety of C++ features are not currently supported by SWIG. Here is the
- short and incomplete list:
- <p>
- <ul>
- <li>Overloaded methods and functions. SWIG wrappers don't know how to resolve name
- conflicts so you must give an alternative name to any overloaded method name using the
- %name directive like this:
- <blockquote>
- <pre>
- void foo(int a);
- %name(foo2) void foo(double a, double b);
- </pre>
- </blockquote>
- <p>
- <li>Overloaded operators. Not supported at all. The only workaround for this is
- to write a helper function. For example:
- <blockquote>
- <pre>
- %inline %{
- Vector *vector_add(Vector *a, Vector *b) {
- ... whatever ...
- }
- %}
- </pre>
- </blockquote>
- <p>
- <li>Namespaces. Not supported at all. Won't be supported until SWIG2.0 (if at all).
- <p>
- <li>Dave's snide remark: Like a large bottle of strong Tequilla, it's better to
- use C++ in moderation.
- </ul>
- <hr>
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