Marshaling code

Hello Arijeet Ghosh, In below example 'MessageBox' method is calling from user32.dll unmanaged dll. One more thing you should know why we are using extern modifier, extern modifier is used when need call method from unmanaged dll.

Example 1:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;
namespace DllImportSample
{
public partial class frmDllImportSample : Form
{
[DllImport("user32.dll")]
private static extern int MessageBox(IntPtr hWnd, String lpText, String lpCaption, uint uType);
public frmDllImportSample()
{
InitializeComponent();
}
private void btnMessageBox_Click(object sender, EventArgs e)
{ MessageBox(new IntPtr(this.Handle.Int32()), @"Calling MessageBox Win32 API from C#", @"MessageBox", 0);
System.Windows.Forms.MessageBox.Show(@"This is C# MessageBox!", @"MessageBox");
}
}
}

Example 2:

internal sealed class Test
{
[DllImport("testlib.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true)]
public static extern IntPtr DataReceived(byte[] signals);
}

Note that when you call it, you will need to use Marshall.Copy to get the data out, but this will require that you know the length of the data.

IntPtr fooPtr = Test.DataRecieved(signals);
var foo = new byte[LENGTH];
Marshall.Copy(fooPtr, foo, 0, LENGTH);

4 Replies

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Rajanikant Hawaldar6y ago
Accepted answer
Hello Arijeet Ghosh, In below example 'MessageBox' method is calling from user32.dll unmanaged dll. One more thing you should know why we are using extern modifier, extern modifier is used when need call method from unmanaged dll.

Example 1:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace DllImportSample
{
    public partial class frmDllImportSample : Form
    {
        [DllImport("user32.dll")]
        private static extern int MessageBox(IntPtr hWnd, String lpText, String lpCaption, uint uType);

        public frmDllImportSample()
        {
            InitializeComponent();
        }

        private void btnMessageBox_Click(object sender, EventArgs e)
        {                          MessageBox(new IntPtr(this.Handle.Int32()), @"Calling MessageBox Win32 API from C#", @"MessageBox", 0);

            System.Windows.Forms.MessageBox.Show(@"This is C# MessageBox!", @"MessageBox");

        }
    }
}
Example 2:
internal sealed class Test
{
    [DllImport("testlib.dll", CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true)]
    public static extern IntPtr DataReceived(byte[] signals);

}
Note that when you call it, you will need to use Marshall.Copy to get the data out, but this will require that you know the length of the data.
IntPtr fooPtr = Test.DataRecieved(signals);
var foo = new byte[LENGTH];
Marshall.Copy(fooPtr, foo, 0, LENGTH);
Rajanikant Hawaldar6y ago
https://forums.asp.net/t/1477303.aspx?Before+I+use+DllImport+shall+i+register+the+DLL+file+
https://stackoverflow.com/questions/8836093/how-can-i-specify-a-dllimport-path-at-runtime
https://www.dotnetperls.com/dllimport
Arijeet Ghosh6y ago
Thank you very much Sir...sorry I haven't looked at the second eample.
but where did testlib.dll come from and where does DllImprt function looks in(directory).
Arijeet Ghosh6y ago
Thank you very much. I don't know vc++. What I require is that a custom function written in VC++, which returns an integer or a string. I'll call that funtion and store the value in C#'s function. Please give an example.....