New example
git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@775 626c5289-ae23-0410-ae9c-e8d60b6d4f22
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Dave Beazley
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19
Examples/python/class/Makefile
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19
Examples/python/class/Makefile
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TOP = ../..
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SWIG = $(TOP)/../swig
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CXXSRCS = example.cxx
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TARGET = example
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INTERFACE = example.i
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LIBS = -lm
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all::
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$(MAKE) -f $(TOP)/Makefile CXXSRCS='$(CXXSRCS)' SWIG='$(SWIG)' \
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TARGET='$(TARGET)' INTERFACE='$(INTERFACE)' python_cpp
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static::
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$(MAKE) -f $(TOP)/Makefile CXXSRCS='$(CXXSRCS)' SWIG='$(SWIG)' \
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TARGET='mypython' INTERFACE='$(INTERFACE)' python_cpp_static
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clean::
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rm -f *_wrap* *.o *~ *.so mypython *.pyc .~* core
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check: all
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28
Examples/python/class/example.cxx
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28
Examples/python/class/example.cxx
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/* File : example.c */
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#include "example.h"
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#include <math.h>
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/* Move the shape to a new location */
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void Shape::move(double dx, double dy) {
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x += dx;
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y += dy;
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}
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int Shape::nshapes = 0;
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double Circle::area() {
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return M_PI*radius*radius;
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}
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double Circle::perimeter() {
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return 2*M_PI*radius;
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}
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double Square::area() {
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return width*width;
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}
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double Square::perimeter() {
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return 4*width;
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}
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39
Examples/python/class/example.h
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39
Examples/python/class/example.h
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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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11
Examples/python/class/example.i
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11
Examples/python/class/example.i
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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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70
Examples/python/class/example.py
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70
Examples/python/class/example.py
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# file: example.py
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# This file illustrates the low-level C++ interface
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# created by SWIG. In this case, all of our C++ classes
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# get converted into function calls.
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import example
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# ----- Object creation -----
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print "Creating some objects:"
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c = example.new_Circle(10)
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print " Created circle", c
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s = example.new_Square(10)
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print " Created square", s
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# ----- Access a static member -----
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print "\nA total of", example.cvar.Shape_nshapes,"shapes were created"
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# ----- Member data access -----
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# Set the location of the object
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# Notice how we can do this using functions specific to
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# the 'Circle' class.
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example.Circle_x_set(c, 20)
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example.Circle_y_set(c, 30)
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# Now use the same functions in the base class
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example.Shape_x_set(s,-10)
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example.Shape_y_set(s,5)
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print "\nHere is their current position:"
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print " Circle = (%f, %f)" % (example.Shape_x_get(c), example.Shape_y_get(c))
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print " Square = (%f, %f)" % (example.Shape_x_get(s), example.Shape_y_get(s))
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# ----- Call some methods -----
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print "\nHere are some properties of the shapes:"
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for o in [c,s]:
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print " ", o
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print " area = ", example.Shape_area(o)
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print " perimeter = ", example.Shape_perimeter(o)
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# Notice how the Shape_area() and Shape_perimeter() functions really
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# invoke the appropriate virtual method on each object.
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# ----- Try to cause a type error -----
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print "\nI'm going to try and break the type system"
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try:
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# Bad script!
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Square_area(c) # Try to invoke Square method on a Circle
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print " Bad bad SWIG!"
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except:
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print " Well, it didn't work. Good SWIG."
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# ----- Delete everything -----
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print "\nGuess I'll clean up now"
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# Note: this invokes the virtual destructor
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example.delete_Shape(c)
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example.delete_Shape(s)
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print example.cvar.Shape_nshapes,"shapes remain"
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print "Goodbye"
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239
Examples/python/class/index.html
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239
Examples/python/class/index.html
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<html>
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<head>
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<title>SWIG:Examples:python:class</title>
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</head>
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<body bgcolor="#ffffff">
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<tt>SWIG/Examples/python/class/</tt>
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<hr>
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<H2>Wrapping a simple C++ class</H2>
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<tt>$Header$</tt><br>
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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++ -python example.i
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</pre>
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</blockquote>
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<h2>A sample Python script</h2>
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Click <a href="example.py">here</a> to see a script that calls the C++ functions from Python.
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<h2>Key points</h2>
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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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c = example.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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example.Circle_x_set(c,15) # Set member data
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x = example.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 or the derived class can be
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used in the function name as shown above. Of course, it would probably be more
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proper to just use the base class version 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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print "The area is ", example.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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example.Shape_area(c) # Works (c is a Shape)
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example.Circle_area(c) # Works (c is a Circle)
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example.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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example.delete_Shape(c) # Deletes a shape
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</pre>
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</blockquote>
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(Note: destructors are currently not inherited. This might change later).
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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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n = example.cvar.Shape_nshapes # Get a static data member
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example.cvar.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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<h2>General Comments</h2>
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<ul>
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<li>This low-level interface is not the only way to handle C++ code. Shadow classes
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provide a much higher-level interface.
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<p>
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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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<p>
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<li>A wide variety of C++ features are not currently supported by SWIG. Here is the
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short and incomplete list:
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<p>
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<ul>
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<li>Overloaded methods and functions. SWIG wrappers don't know how to resolve name
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conflicts so you must give an alternative name to any overloaded method name using the
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%name directive like this:
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<blockquote>
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<pre>
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void foo(int a);
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%name(foo2) void foo(double a, double b);
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</pre>
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</blockquote>
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<p>
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<li>Overloaded operators. Not supported at all. The only workaround for this is
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to write a helper function. For example:
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<blockquote>
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<pre>
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%inline %{
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Vector *vector_add(Vector *a, Vector *b) {
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... whatever ...
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}
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%}
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</pre>
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</blockquote>
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<p>
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<li>Namespaces. Not supported at all. Won't be supported until SWIG2.0 (if at all).
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<p>
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<li>Templates. Not supported at all. SWIG throws out anything that looks like a template.
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You can work around the problem by aliasing a template class behind a typedef however.
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For example:
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<blockquote>
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<pre>
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%{
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typedef vector<int> IntVector;
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%}
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class IntVector {
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public:
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... methods ...
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};
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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>There is no guarantee that an extremely complex C++ application will be able to compile
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as a Python extension. Sorry.
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<p>
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<li>Dave's snide remark: Like a large bottle of strong Tequilla, it's better to
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use C++ in moderation.
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</ul>
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<hr>
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</body>
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</html>
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@ -18,6 +18,7 @@ be used to wrap a C function, a global variable, and a constant.
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certain C declarations are turned into constants.
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<li><a href="variables/index.html">variables</a>. An example showing how to access C global variables from Python.
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<li><a href="value/index.html">value</a>. How to pass and return structures by value.
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<li><a href="class/index.html">class</a>. Wrapping a simple C++ class.
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</ul>
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<h2>Compilation Issues</h2>
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