Using DLL calls

Posted on 2000-03-23
Last Modified: 2010-04-04
I had created a dll with the MFC Wizard (Project of the type Win32 Dynamic-Link Library). This dll had just one function call in it as shown below.

extern "C"
__declspec (dllexport) __int32  pipt_teste( __int32 *pt )
      *pt = 50;
      return 0;

And then I tried to use it in my delphi program.

In the mainframe I created a menu option called 'Test', and then when this option was called it create a form dynamically with a button in it. When the button was activated, it call the pipt_teste. The code is shown below:

function pipt_teste( pTeste : Pointer ) : Integer; stdcall; external 'prjDLL.dll'


procedure TFrm.BtOkClick(Sender: TObject);
   teste : Integer;

   if pipt_teste( @teste ) then
      modalResult := mrOk
      modalResult := mrAbort;


What happening was, after calling the pipt_teste function, something was lost, the modalResult was not available more, the same happened to all attributes within the class.

What is wrong with my code?

Thanks for the help.
Question by:mauling

Expert Comment

ID: 2650600
You are using the wrong calling convention. Try

function pipt_teste( pTeste : Pointer ) : Integer; cdecl; external 'prjDLL.dll'

LVL 15

Expert Comment

ID: 2651396
Try this:

function pipt_teste(var pTeste : longint ) : Integer; stdcall; external 'prjDLL.dll'

It cannot be CDECL, because it's declared as STDCALL in the DLL.



Accepted Solution

zealsoft earned 100 total points
ID: 2651517
The declrarion of MFC DLL is not correct. If you use __declspec (dllexport) to declare a function, VC will use decorated names, so you can't call it correctly in Delphi.You need to change as follows,

1. Change your C function:
extern "C"
__stdcall __int32  pipt_teste( __int32 *pt )
*pt = 50;
return 0;

2. Createa prjDLL.def file and add it to your VC project.
In the .def file:

3. Change your Delphi declation
function pipt_teste(var pTeste : integer ) : Integer; stdcall; external 'prjDLL.dll'

4. When you call the function, you can use
 if pipt_teste( teste ) then
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LVL 12

Expert Comment

ID: 2651643

Expert Comment

ID: 2651979
Where does anyone see STDCALL as the calling convention in the original question's DLL code? The answer is, was and will always be the calling convention.change it in the DLL or change it in the Delphi app, but change it.


Expert Comment

ID: 2659384

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