"Attempted to read or write protected memory. This is often an indication that other memory is corrupt." Delphi7 DLL from C#

Question

I am facing a problem calling a Delphi 7 DLL file from C#. I am new to C# and don't know Delphi that much and I don't need to really knows that much. I just need to get this problem solved as soon as possible.

I am trying to call the dll from C# but I get this error : "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

And I have no clue why it is happening . As you will see in my Delphi code , I'm not trying to return any value . I just need to send some commands on the COM port. Please if anyone can help me out of here :(

Delphi DLL code:

library Project2;


uses
  SysUtils,
  ComPort,
  Classes;

var com1:TComport ;

{$R *.res}
procedure moveforward; export;
begin
  com1.WriteAnsiString('#20 P1528 CR'+sLineBreak);
  com1.WriteAnsiString('#7 P1465 CR'+sLineBreak);
end;

procedure movebackward; export;
begin
  comport1.WriteAnsiString('#7 P1528 CR'+sLineBreak);
  comport1.WriteAnsiString('#20 P1465 CR'+sLineBreak);
end;

procedure stopmove;export;
begin
  comport1.WriteAnsiString('#20 P1500 CR'+sLineBreak);
  comport1.WriteAnsiString('#7 P1500 CR'+sLineBreak);
end;

procedure catch; export;
begin
  comport1.WriteAnsiString('#2 P2120 T2000 CR'+sLineBreak); //arm
  comport1.WriteAnsiString('#30 P2260 T500 CR'+sLineBreak); //gripper
end;

procedure initialize; export;
begin
  comport1.WriteAnsiString('#2 P2184 T1000 CR'+sLineBreak); //arm
  comport1.WriteAnsiString('#30 P1980 T2000 CR'+sLineBreak); //gripper
end;

exports  
  moveforward, movebackward, stopmove, catch, initialize;

begin
end.

C# Code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication3
{
    public partial class Form1 : Form
    {
        [System.Runtime.InteropServices.DllImport("Project2.dll")]
        public static extern void moveforward();
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            moveforward();
        }
    }
}

Any help will be truly appreciated

Answer 1

EDIT:

Please note, upon further reflection I'm pretty sure this is not the right answer. It's still a bad idea to use mismatched calling conventions (thus my initial instinct that it was the problem) but in this case it is probably not the cause of the GPF.

ORIGINAL:

99% of the time, this error means you got the calling conventions wrong. It's been a while since I wrote in Delphi but I think this will fix your problem:

procedure moveforward; export; stdcall;

The calling convention is normally not an issue when you're only using a single compiler, because everything uses the same one. It can be a problem when you mix languages, or even if you mix different vendor's compilers. The calling convention determines which end of the call has to clean up parameters; if both sides try to do that it's likely to cause a GPF.

By default, the DllImport attribute uses a calling convention of CallingConvention.StdCall, though you can override that in the attribute itself. Unfortunately, Delphi's default calling convention is a type that isn't supported (alternatively called fastcall or register), so your only option is to change the Delphi side to use stdcall.