Question

My application has to provide the ability of calling different functions and procedures from external DLLs. So we don’t know parameters’ count and their types. What should I do to do this?

Let me explain it more. My application is a RAD tool and it has its own scripting and syntax… I want to let users to use ANY dll file and call any function or procedure they want. I can’t use the simple method of calling dll (LoadLibrary and then GetProcAddress) because I don’t know what type the GetProcAddress refers to ( var Proc:procedure (A:??;B:??;...) ).

Answer 1

This is a simple example that works on my machine, but I am not an expert on the subject.

procedure TForm4.Button1Click(Sender: TObject);
var
  hmod: HMODULE;
  paddr: pointer;         
  c1, c2, ret: cardinal;
begin
  c1 := 400; //frequency
  c2 := 2000; // duration

  hmod := LoadLibrary('kernel32'); // Of course, the name of the DLL is taken from the script
  if hmod <> 0 then
    try
      paddr := GetProcAddress(hmod, 'Beep'); // ...as is the name of the exported function
      if paddr <> nil then
      begin
        // The script is told that this function requires two cardinals as
        // arguments. Let's call them c1 and c2. We will assume stdcall
        // calling convention. We will assume a 32-bit return value; this
        // we will store in ret.
        asm
          push c2
          push c1
          call [paddr]
          mov ret, eax
        end;
      end;
    finally
      FreeLibrary(hmod);
    end;
end;