Unmanaged C++ Dll call From Managed C# Application

Here you see the steps for using a simple C++ DLL in a C# application.



Here you see the steps for using a simple C++ dll in C# in .Net Framework 4.

1. Open Visual C++ Win 32 Project

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2. In Application Setting Chose Dll & select Empty Project

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3. The Solution will Look like

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4. Add New Item(*.cpp) in Source Folder

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5. Select cpp File

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6. Write Down the simple Code in cpp file:

#include <stdio.h>

extern "C" 
{
       __declspec(dllexport) int add(int a,int b)
       {
              return a+b;
       }
       __declspec(dllexport) int subtract(int a,int b)
       {
              return a-b;
       }
}


7. Now export *.res file in Resource Folder For Version information


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8. Now Solution Explorer will looks like

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9. After Compile you will see the Debug Folder as

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10. Now Our Unmanaged Dll is Ready. We build a Managed C# App

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11. Design is like

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12. Code is as follows

[DllImport("OurDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int subtract(int a, int b);

        private void button2_Click(object sender, EventArgs e)
        {
            int x = Convert.ToInt32(textBox1.Text);
            int y = Convert.ToInt32(textBox2.Text);
            int z = subtract(x, y);
            MessageBox.Show("Required Answer is " + Convert.ToString(z), "Answer", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }




13. Out put will be

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14. In case of Previous Version of .net Code will be (3.5)

        [DllImport("OurDll.dll")]
        public static extern int subtract(int a, int b);

        private void button2_Click(object sender, EventArgs e)
        {
            int x = Convert.ToInt32(textBox1.Text);
            int y = Convert.ToInt32(textBox2.Text);
            int z = subtract(x, y);
            MessageBox.Show("Required Answer is " + Convert.ToString(z), "Answer", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }


15. Out put will be same for both

Few Words:

extern "C"-> which help to show all code within brackets from  outside

__declspec(dllexport) int add(int a,int b)-> a prefix which makes DLL functions available from your external application

In .net Frame Work 3.5 or Previous the code is like

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

For .net Frame Work 4 the code will be,

[DllImport("OurDll.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int add(int a,int b);

if only write, like framework 3.5 [DllImport("OurDll.dll")]

you get an exception like  … the managed PInvoke signature does not match the unmanaged signature …"
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Now you can call an C++ dll from your C# application (.net frame work 4)

Thank You!

Tanmay Sarkar