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Reference example like the other languages, all working

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git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk/SWIG@4529 626c5289-ae23-0410-ae9c-e8d60b6d4f22
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William S Fulton 2003-03-12 20:47:39 +00:00
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runme
*_wrap.c
*_wrap.cxx
*.iltmp
*.cs
*.dll
*.dsw
*.exp
*.lib
*.ncb
*.opt
*.plg
Release
Debug

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TOP = ../..
SWIG = $(TOP)/../swig
CXXSRCS = example.cxx
TARGET = example
INTERFACE = example.i
SWIGOPT =
all:: csharp
csharp::
$(MAKE) -f $(TOP)/Makefile CXXSRCS='$(CXXSRCS)' SWIG='$(SWIG)' \
SWIGOPT='$(SWIGOPT)' TARGET='$(TARGET)' INTERFACE='$(INTERFACE)' csharp_cpp
cscc *.cs -o runme
clean::
$(MAKE) -f $(TOP)/Makefile csharp_clean
check: all

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/* File : example.cxx */
#include "example.h"
#include <stdio.h>
#include <stdlib.h>
Vector operator+(const Vector &a, const Vector &b) {
Vector r;
r.x = a.x + b.x;
r.y = a.y + b.y;
r.z = a.z + b.z;
return r;
}
char *Vector::print() {
static char temp[512];
sprintf(temp,"Vector %x (%g,%g,%g)", this, x,y,z);
return temp;
}
VectorArray::VectorArray(int size) {
items = new Vector[size];
maxsize = size;
}
VectorArray::~VectorArray() {
delete [] items;
}
Vector &VectorArray::operator[](int index) {
if ((index < 0) || (index >= maxsize)) {
printf("Panic! Array index out of bounds.\n");
exit(1);
}
return items[index];
}
int VectorArray::size() {
return maxsize;
}

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/* File : example.h */
class Vector {
private:
double x,y,z;
public:
Vector() : x(0), y(0), z(0) { };
Vector(double x, double y, double z) : x(x), y(y), z(z) { };
friend Vector operator+(const Vector &a, const Vector &b);
char *print();
};
class VectorArray {
private:
Vector *items;
int maxsize;
public:
VectorArray(int maxsize);
~VectorArray();
Vector &operator[](int);
int size();
};

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/* File : example.i */
/* This file has a few "typical" uses of C++ references. */
%module example
%{
#include "example.h"
%}
class Vector {
public:
Vector(double x, double y, double z);
~Vector();
char *print();
};
/* This helper function calls an overloaded operator */
%inline %{
Vector addv(Vector &a, Vector &b) {
return a+b;
}
%}
/* Wrapper around an array of vectors class */
class VectorArray {
public:
VectorArray(int maxsize);
~VectorArray();
int size();
/* This wrapper provides an alternative to the [] operator */
%extend {
Vector &get(int index) {
return (*self)[index];
}
void set(int index, Vector &a) {
(*self)[index] = a;
}
}
};

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<html>
<head>
<title>SWIG:Examples:java:reference</title>
</head>
<body bgcolor="#ffffff">
<tt>SWIG/Examples/java/reference/</tt>
<hr>
<H2>C++ Reference Handling</H2>
<tt>$Header$</tt><br>
<p>
This example tests SWIG's handling of C++ references. Since C++
references are closely related to pointers (as both refer to a
location in memory), SWIG simply collapses all references into
pointers when creating wrappers.
<h2>Some examples</h2>
References are most commonly used as function parameter. For example,
you might have an operator like this:
<blockquote>
<pre>
Vector operator+(const Vector &a, const Vector &b) {
Vector result;
result.x = a.x + b.x;
result.y = a.y + b.y;
result.z = a.z + b.z;
return result;
}
</pre>
</blockquote>
or a function:
<blockquote>
<pre>
Vector addv(const Vector &a, const Vector &b) {
Vector result;
result.x = a.x + b.x;
result.y = a.y + b.y;
result.z = a.z + b.z;
return result;
}
</pre>
</blockquote>
In these cases, SWIG transforms everything into a pointer and creates a wrapper
that looks like this:
<blockquote>
<pre>
Vector wrap_addv(Vector *a, Vector *b) {
return addv(*a,*b);
}
</pre>
</blockquote>
Occasionally, a reference is used as a return value of a function
when the return result is to be used as an lvalue in an expression.
The prototypical example is an operator like this:
<blockquote>
<pre>
Vector &operator[](int index);
</pre>
</blockquote>
or a method:
<blockquote>
<pre>
Vector &get(int index);
</pre>
</blockquote>
For functions returning references, a wrapper like this is created:
<blockquote>
<pre>
Vector *wrap_Object_get(Object *self, int index) {
Vector &result = self->get(index);
return &result;
}
</pre>
</blockquote>
The following <a href="example.h">header file</a> contains some class
definitions with some operators and use of references.
<h2>SWIG Interface</h2>
SWIG does NOT support overloaded operators so it can not directly build
an interface to the classes in the above file. However, a number of workarounds
can be made. For example, an overloaded operator can be stuck behind a function
call such as the <tt>addv()</tt> function above. Array access can be handled
with a pair of set/get functions like this:
<blockquote>
<pre>
class VectorArray {
public:
...
%addmethods {
Vector &get(int index) {
return (*self)[index];
}
void set(int index, Vector &a) {
(*self)[index] = a;
}
}
...
}
</pre>
</blockquote>
Click <a href="example.i">here</a> to see a SWIG interface file with these additions.
<h2>Sample Java program</h2>
Click <a href="main.java">here</a> to see a Java program that manipulates some C++ references.
<h2>Notes:</h2>
<ul>
<li>C++ references primarily provide notational convenience for C++
source code. However, Java only supports the 'x.a'
notation so it doesn't much matter.
<p>
<li>When a program returns a reference, a pointer is returned.
Unlike return by value, memory is not allocated to hold the
return result.
<p>
<li>SWIG has particular trouble handling various combinations of references
and pointers. This is side effect of an old parsing scheme and
type representation that will be replaced in future versions.
</ul>
<hr>
</body>
</html>

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// This example illustrates the manipulation of C++ references in C#.
using System;
public class runme {
public static void Main()
{
Console.WriteLine( "Creating some objects:" );
Vector a = new Vector(3,4,5);
Vector b = new Vector(10,11,12);
Console.WriteLine( " Created " + a.print() );
Console.WriteLine( " Created " + b.print() );
// ----- Call an overloaded operator -----
// This calls the wrapper we placed around
//
// operator+(const Vector &a, const Vector &)
//
// It returns a new allocated object.
Console.WriteLine( "Adding a+b" );
Vector c = example.addv(a,b);
Console.WriteLine( " a+b = " + c.print() );
// Note: Unless we free the result, a memory leak will occur if the -noproxy commandline
// is used as the proxy classes define finalizers which call the Dispose() method. When
// -noproxy is not specified the memory management is controlled by the garbage collector.
// You can still call Dispose(). It will free the c++ memory immediately, but not the
// C# memory! You then must be careful not to call any member functions as it will
// use a NULL c pointer on the underlying c++ object. We set the C# object to null
// which will then throw a C# exception should we attempt to use it again.
c.Dispose();
c = null;
// ----- Create a vector array -----
Console.WriteLine( "Creating an array of vectors" );
VectorArray va = new VectorArray(10);
Console.WriteLine( " va = " + va.ToString() );
// ----- Set some values in the array -----
// These operators copy the value of Vector a and Vector b to the vector array
va.set(0,a);
va.set(1,b);
// This works, but it would cause a memory leak if -noproxy was used!
va.set(2,example.addv(a,b));
// Get some values from the array
Console.WriteLine( "Getting some array values" );
for (int i=0; i<5; i++)
Console.WriteLine( " va(" + i + ") = " + va.get(i).print() );
// Watch under resource meter to check on this
Console.WriteLine( "Making sure we don't leak memory." );
for (int i=0; i<1000000; i++)
c = va.get(i%10);
// ----- Clean up -----
// This could be omitted. The garbage collector would then clean up for us.
Console.WriteLine( "Cleaning up" );
va.Dispose();
a.Dispose();
b.Dispose();
}
}