Interfacing Parallel Port using Qt

I've been in a situation today where I wanted a quick app to interact with the parallel port. Although it is no big deal, it was my first time. So I wanted to document it and make a simple application.

There is no Qt API to access the parallel port, so there was no other way but using an extra DLL: inpout32.dll. The core of code in brief is like that:

Note: the DLL was not available by default. So I downloaded it and Had the choice to put it in C:\Windows\System32 or just point to it in the application's folder.

*.h

#include <windows.h>

/* prototype (function typedef) for DLL function Inp32: */
typedef short _stdcall (*inpfuncPtr)(short portaddr);
typedef void _stdcall (*oupfuncPtr)(short portaddr, short datum);

private:
    HINSTANCE hLib;
    inpfuncPtr inp32;
    oupfuncPtr oup32;
    short portData; //must be in hex
    int portNumber; //must be in hex

*.cpp

/* Load the library */
hLib = LoadLibraryA("inpout32.dll");

/* get the address of the function */
inp32 = (inpfuncPtr) GetProcAddress(hLib, "Inp32");
oup32 = (oupfuncPtr) GetProcAddress(hLib, "Out32");

Note: I faced an encoding error with LoadLibrary(). so I used LoadLibraryA() instead.

Reading

portData = (inp32)(portNumber);

Writing

(oup32)(portNumber, portData);

A useful hint for converting from QString to Hex/Binary, and vise versa

//QString to Hex
portNumber = myString.toInt(&ok, 16);

//Hex to QString
myString = QString::number(portData, 16);

Note: Icons in this application are free! http://www.freedesktop.org/

Download source code
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Resources:
Parallel Port Output On Windows XP using Qt4 and C++
MinGW: char to WCHAR