SWIG:Examples:perl5:class

SWIG/Examples/perl5/class/

Wrapping a simple C++ class

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.

The C++ Code

Suppose you have some C++ classes described by the following (and admittedly lame) header file:

/* 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();
};

The SWIG interface

A simple SWIG interface for this can be built by simply grabbing the header file like this:

/* File : example.i */
%module example

%{
#include "example.h"
%}

/* Let's just grab the original header file here */
%include "example.h"

Note: when creating a C++ extension, you must run SWIG with the -c++ option like this:

% swig -c++ -perl example.i

A sample Perl script

Click here to see a script that calls the C++ functions from Perl.

Key points

To create a new object, you call a constructor like this:
```
$c = new example::Circle(10.0);
```

You can access member data like so:

$c->{x} = 15;    # Set member data
$x = $c->{x};    # Get member data

To invoke a member function, you simply do this:
```
print "The area is ", $c->area();
```
To invoke a destructor, simply do this:
```
$c->DESTROY();   # Deletes a shape
```

Static member variables are wrapped like so:

$n = $example::Shape::nshapes;    # Get a static data member
$example::Shapes::nshapes = 13;   # Set a static data member

General Comments

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.
C++ Namespaces - %nspace isn't yet supported for Perl.