Newbie Question:- Dynamically Loading Libraries 1

[Jasonic]

Dear All

I have read the online help about loadLibrary and Calling dynamically loadable libraries, but still seem to have trouble.

I have an MDI application that hopefully extends the functionality of an application through the API's supplied

I have read the application API example for a C program

I.E
#include apiproto.h
#define SZ_MODEL_LEN 200
long lCnx ;
long lQuery ;
long lStatus ; /* to store error code */
char szModel[SZ_MODEL_LEN] ;
/* dll initialization */
AmStartup();
/* Open a connection */
lCnx = AmOpenConnection(connection,user,pword);

In the section about calling dynamic libraries I have to declare the functions/procedures requried, therefore I created

procedure AmStartUp(); external 'MyDll.dll';

But it complains about this

Can anyone point me in the right direction or provide easier to understand information about loading and calling dll functions

Thanks

Jason Thomas
AssetCenter Consultant

http://www.corviz.com

 

[michaenh]

Hi
Try this...
procedure AmStartUp; stdcall; external 'MyDll.dll';

procedure TForm1.BtnClick(Sender: TObject);
begin
AmStartUp;
end;

michaenh

 

[Jasonic]

Michaenh

I seem to be getting an error just after the word external the comipler complains about 'Field definition not allowed after methods or properties'

any ideas, have I put the code in the wrong place?

Cheers Jason Thomas
AssetCenter Consultant

http://www.corviz.com

 

[TonHu]

This is part of my code for dynamically connecting to functions from some DLL: It is in a unit, and it's partly an original work, but also some parts are from external sources. This code has no real function as published here. (Disclaimer)

...
Var
NetShareAdd: function(ServerName : PChar; ShareLevel : SmallInt; Buffer : Pointer; Size : Word) : Integer; StdCall;
NetShareAddNT: function(ServerName : PChar; ShareLevel : DWord; Buffer : Pointer; Error : Pointer) : Integer; StdCall;
...
Var Hand : LongWord;
Initialization
If IsNT then
    Hand := LoadLibrary('NetApi32')
Else
    Hand := LoadLibrary('SvrApi');
If Hand <> 0 then
Begin
    If IsNT then
        NetShareAddNT := GetProcAddress(Hand,'NetShareAdd')
    Else
        NetShareAdd := GetProcAddress(Hand,'NetShareAdd');
End;
Finalization
    If Hand <> 0 then
        FreeLibrary(Hand);

HTH
TonHu

 

[michaenh]

You have a dll as ex.'MyDll.dll' that you have created in C or C++ and a procedure AmStartUp which just give a msg 'hi' and a function which returns 123.


To get that proc from your unit:
unit CallCppF;

interface

uses
SysUtils, etc...

type
TForm1 = class(TForm)
BtnProc: TButton;
BtnFunc: TButton;
....
procedure BtnClick(Sender: TObject);
procedure BtnDoubleClick(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.DFM}

{definition of the functions or procedure of the DLL}
procedure AmStartUp; stdcall; external 'MyDll.dll';
function Triple: Integer; stdcall; external 'MyDll.dll';

procedure TForm1.BtnClick(Sender: TObject);
begin
AmStartUp; //trigger the dll's proc -> msg hi
end;

procedure TForm1.BtnDoubleClick(Sender: TObject);
begin
ShowMessage(IntToStr(Triple)); //trigger the dll's func -> returns 123 msg
end;

You could also do as TonHu suggested.

 

[michaenh]

if your function dll have a name..
ex.

function Add (A, B: Integer): Integer;
stdcall; external 'CPPDLL.DLL' name '@Add$qqsii';