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| author | Lorry Tar Creator <lorry-tar-importer@baserock.org> | 2009-08-18 20:56:02 +0000 |
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| committer | Lorry <lorry@roadtrain.codethink.co.uk> | 2012-09-25 16:59:08 +0000 |
| commit | 9f8a09ed743cedd9547bf0661d518647966ab114 (patch) | |
| tree | 9c7803d3b27a8ec22e91792ac7f7932efa128b20 /Examples/python/class/index.html | |
| download | swig-tarball-master.tar.gz | |
Imported from /srv/lorry/lorry-area/swig-tarball/swig-1.3.40.tar.gz.HEADswig-1.3.40master
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diff --git a/Examples/python/class/index.html b/Examples/python/class/index.html new file mode 100644 index 0000000..12c5ede --- /dev/null +++ b/Examples/python/class/index.html @@ -0,0 +1,216 @@ +<html> +<head> +<title>SWIG:Examples:python:class</title> +</head> + +<body bgcolor="#ffffff"> + + +<tt>SWIG/Examples/python/class/</tt> +<hr> + +<H2>Wrapping a simple C++ class</H2> + +<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. +Proxy 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> +</body> +</html> |