A SWIG Example

SWIG

SWIG is stand along software development tool. It connects code programmed in C and C++ with many high-level programming languages including python. SWIG is used to parse C/C++ interfaces and generate the ‘glue code’ required for the above target languages to call into the C/C++ code.

The idea of SWIG is to create a dynamic python library module, which calls the SDK DLL. The structure is shown below.

The SWIG compiles the DLL and H files under the instruction of the .i file (SWIG configuring file). The SWIG project generates the Python Dynamic Library file (pyd). This pyd file can be imported to python.

A Basic But Not Simple Example

github repo

1. Make a little DLL project.

In the repo, this little DLL project is xiaoAdd. There is a class AddTest. This class has only one useful member function add.

AddTest.h

/* AddTest.h */
#pragma once

class __declspec(dllexport) AddTest
{
public:
    AddTest(void);
    ~AddTest(void);
    int add(int a, int b);
};

AddTest.cpp

/* AddTest.cpp */
#include "AddTest.h"

AddTest::AddTest(void)
{
}

AddTest::~AddTest(void)
{
}

int AddTest::add(int a, int b)
{
    return a+b;
}

Compile this project and get the results.

xiaoAdd.dll
xiaoAdd.lib
xiaoAdd.pdb

2. Make a Python dynamic module

In the github repo, this module is xiaoA

AddTest.h

/* AddTest.h */
#pragma once

class __declspec(dllimport)AddTest
{
public:
    AddTest(void);
    ~AddTest(void);
    int add(int a, int b);
};

xiaoAddModule.i

/* xiaoAddModule.i */
%module xiaoAddModule

%{
/* Put header files here or function declarations like below */
#include "AddTest.h"
%}

%include <windows.i>
%include "AddTest.h"

1. Compile the xiaoAddModule.i for xiaoAddModule_wrap.cxx.

2. Build the project (Reference) including

xiaoAddModule_wrap.cxx
AddTest.h
xiaoAdd.dll
xiaoAdd.lib

3. Get the results

_xiaoAddModule.exp
_xiaoAddModule.lib
_xiaoAddModule.pdb
_xiaoAddModule.pyd
xiaoAddModule.py
xiaoAddmodule.pyc

4. Write the Python script within the folder where above results are located.

test.py

# test.py
import xiaoAddModule
instance = xiaoAddModule.AddTest()
print 'The result of 2 + 3 = %r' % (instance.add(2,3))
wait = input("PRESS ENTER TO EXIT.")

A Complex Solution For A Complex Example

When wrapping a complex 3rd party library, there are lots of classes and functions. We want to keep this interface nice and clean. A C++ wrapper is implemented as shown below.