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acmDriverEnum problem

Posted on 1997-04-07
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Last Modified: 2010-04-03
I'm trying to link msacm32.dll to my Delphi program.
Everything goes well until I try to call acmDriverEnum -
I receive different Error messages, sometimes Windows symply
hungs and so on. I think the problem is how to correctly
declare the Callback function and pass it's address to
acmDriverEnum. If somebody has a piece of working Delphi
code which calls acmDriverEnum - would you like to send it
here?
Thank you. Alex.
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Question by:Madorsky
  • 2
3 Comments
 
LVL 3

Expert Comment

by:sperling
ID: 1335225
As you haven't posted the failing source, it's kind of hard to tell what the problem is.

But, a common mistake is to forget the stdcall directive. Almost all callback functions should be declared using this.


E.g.

procedure ThisIsACallback(AParam, AnotherParam : DWORD); stdcall;
begin
end;


If this isn't the problem, leave me a comment along with some source code, and I'll have a look at it.


Regards,

Erik.
0
 

Author Comment

by:Madorsky
ID: 1335226
var
  acmGetVersion: function : DWORD;
  acmDriverEnum: function(fnCallback: Pointer; dwInstance,                           fdwEnum: DWORD) : DWORD ;


function RealCallback
         (
              hadid: DWORD;
              dwInstance, fdwSupport: DWORD
         ):Boolean; stdcall;
{I've tried also cdecl, pascal and so on - without success}
begin
     Result := True;
end;

procedure TForm1.Button1Click(Sender: TObject);
var lhDll, sfHandle: DWORD;
begin

     lhDll := LoadLibrary ('msacm32.dll');
     if lhDll < 32 then
     begin
          MessageDlg('No DLL', mtError, [mbOk], 0);
     end;

     @acmGetVersion := GetProcAddress(lhDll, 'acmGetVersion');
     if @acmGetVersion = nil then
     begin
          MessageDlg('No acmGetVersion', mtError, [mbOk], 0);
     end;

     @acmDriverEnum := GetProcAddress(lhDll, 'acmDriverEnum');
     if @acmDriverEnum = nil then
     begin
          MessageDlg('No acmDriverEnum', mtError, [mbOk], 0);
     end;

     Label1.Caption := IntToHex(acmGetVersion, 8);
{The result is $04000000 - looks good}

     acmDriverEnum(@RealCallBack, 0, 0);
{Here it hungs}
end;
{I've also tried to create the procedural type and variable of
that type, and pass that var to acmDriverEnum by reference -
result is the same.}

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LVL 3

Accepted Solution

by:
sperling earned 50 total points
ID: 1335227
var
  acmGetVersion: function : DWORD;
  acmDriverEnum: function(fnCallback: Pointer; dwInstance, fdwEnum: DWORD) : DWORD ;


Here's the error.

Append a stdcall to these lines.

  acmGetVersion: function : DWORD; stdcall;
  acmDriverEnum: function(fnCallback: Pointer; dwInstance, fdwEnum: DWORD) : DWORD ; stdcall;

acmGetVersion works regardless of calling convention, because it doesn't take any parameters, and return value is passed back the same way in all calling conventions. acmDriverEnum expects parameters to be passed using "stdcall", while your declaration passes parameters using the default "register"


Regards

Erik.

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