Delphi DLL Issues - wrong integer value recevied and access violation issue - windows

Question

I'm having trouble getting to grips with DLLs in Delphi 7. I have two problems:
1) The procedure takes an integer parameter - but the dll receives a different value to the one I pass.
2) The application that called the dll crashes with an access violation after the function completes.
Here's my dll code:
library apmDLL;
uses
Classes, Messages, Windows, Dialogs, sysutils ;
const
WM_MY_MESSAGE = WM_USER + 1;
procedure sendtoACRPM (functionKey : integer); stdcall;
begin
showmessage('You sent - '+inttostr(functionKey));
showmessage('Finished Now');
end;
exports sendtoACRPM;
end.
So when I call this with the code below I get:
'Sending - 1'
'You Sent - 1636532'
'Finished Now'
Then the calling application crashes with an access violation.
The calling application looks like this:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, shlobj, shellapi;
const
WM_MY_MESSAGE = WM_USER + 1;
type
TForm1 = class(TForm)
Edit1: TEdit;
Button2: TButton;
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
procedure sendtoACRPM (functionKey : integer) ; external 'apmDLL.dll';
implementation
{$R *.dfm}
procedure TForm1.Button2Click(Sender: TObject);
var
myInt: integer;
begin
myInt := strtoint(edit1.text);
showmessage('Sending - ' + inttostr(myInt));
sendtoACRPM(myInt);
end;
end.
Any ideas what I'm doing wrong here?

Answer 1

You need stdcall both in the DLL and in the calling code declaration. You only have it in the DLL.
Calling conventions need to match on both sides. :-)
procedure sendtoACRPM (functionKey : integer); stdcall; external 'apmDLL.dll';
You should use the standard Windows MessageBox instead of ShowMessage, so that the DLL can be used from non-Delphi applications as well.