THECODEPROGRAM

Let's begin.

Firstly we are going to create a library with QT C++. Below image you can see the how to create a library project in QT.

And do not forget to select the Shared Library for our library like below image.

Now let's write our codes in our library. In here we are going to write some basic mathematical calculations. Below code blocks you will see them.

qtlibraryexample.h

#include "qtlibraryexample.h"
#include <stdio.h>

QtLibraryExample::QtLibraryExample()
{
}

extern "C" double add(int a, int b)
{
    return a + b;
}

extern "C" double subtrack(int a, int b)
{
    return a - b;
}

extern "C" double multiply(int a, int b)
{
    return a * b;
}

extern "C" QTLIBRARYEXAMPLESHARED_EXPORT double divide(int a, int b)
{
    return a / b;
}

qtlibraryexample_global.h

#ifndef QTLIBRARYEXAMPLE_GLOBAL_H
#define QTLIBRARYEXAMPLE_GLOBAL_H

#include <QtCore/qglobal.h>

#if defined(QTLIBRARYEXAMPLE_LIBRARY)
#  define QTLIBRARYEXAMPLESHARED_EXPORT Q_DECL_EXPORT
#else
#  define QTLIBRARYEXAMPLESHARED_EXPORT Q_DECL_IMPORT
#endif

extern "C" __declspec(dllexport) double add(int a, int b);
extern "C" __declspec(dllexport) double subtrack(int a, int b);
extern "C" __declspec(dllexport) double multiply(int a, int b);
extern "C" __declspec(dllexport) double divide(int a, int b);

#endif // QTLIBRARYEXAMPLE_GLOBAL_H

Also do not forget our library is 32bit. We are going to need this information in our C# program. Below image you can see the QT library compiler is compiling 32 bit.

Now we creat a C# application in MS Visual Studio.
First we are going to include Interop Services in our C# project.

using System.Runtime.InteropServices;

And then we are going to define the prototype methods which we defined in our C++ library. These methods must be same as the defined in C++ library.
And then we are going to create the function which will call these methods.

[DllImport("QtLibraryExample.dll")]
static extern double add(int a, int b);

[DllImport("QtLibraryExample.dll")]
static extern double subtrack(int a, int b);

[DllImport("QtLibraryExample.dll")]
static extern double multiply(int a, int b);

[DllImport("QtLibraryExample.dll")]
static extern  double divide(int a, int b);

static void callQtFunctions()
{
    Console.WriteLine("Result of 5 + 7 is " + add(5, 7).ToString());
    Console.WriteLine("Result of 21 - 10 is " + subtrack(21, 10).ToString());
    Console.WriteLine("Result of 9 x 3 is " + multiply(9, 3).ToString());
    Console.WriteLine("Result of 70 / 5 is " + divide(70, 5).ToString());
}

All we have to do call this method in main function.

static void Main(string[] args)
{
    Console.Title = "Using QT Libraries in C# Aplication Example - TheCodeProgram";
    callQtFunctions();
    Console.ReadLine();
}

Below image you can see the project output.

That is all in this article.

You can reach the example application on Github via : https://github.com/thecodeprogram/QtLibraryForCSharpApplication

Have a good managing unmanaged codes.

Burak Hamdi TUFAN.