Question

I am complete new to pascal.
I want to call my function in .dll file in free pascal and I get following error when I run the project:

The procedure entry point GetProcAddress could not be located in the dynamic link library HNLib.dll.

here is the code:

Program Test;
function GetProcAddress : Integer; cdecl; external 'HNLib.dll';
function GetProcAddress : Single; cdecl; external 'HNLib.dll';
procedure GetProcAddress( X : Single); cdecl; external 'HNLib.dll';
procedure GetProcAddress; cdecl; external 'HNLib.dll';
begin
  GetProcAddress( 5.5 );
  readln;
end.

.pas file and dll are in one directory.

Please Help ME!

Answer 1

GetProcAddress is not what you seem to think it is; it’s purpose is to locate named procedures or functions in a DLL and return the address of that function so it can be called from your code. You have to first use LoadLibrary to load the dynamic link library (DLL) into memory, and then pass a handle to that DLL as the first parameter of GetProcAddress and the name of the function whose address you want as the second parameter. If the function can be found in the DLL, it’s address is returned, and you can use that address to call the function.

(In addition, GetProcAddress is pretty Windows-specific, and the majority of functions in the WinAPI are stdcall and not cdecl. Unless you have documentation saying that the functions are using the cdecl calling convention, you should probably use stdcall.)

You would also need at least the Windows unit in your uses clause, since that’s where GetProcAddress and LoadLibrary are declared.

See the WinAPI documentation on LoadLibrary and GetProcAddress for more information.

For a beginning programmer, you’ll probably find it easier to use static linking of the functions instead of dynamic (which you get with GetProcAddress). An example of static linking would be (untested !!!- just a quick code example, since I don’t have ‘HNLib.DLL’ to link against):

// Your Dll import unit
unit MyDllProcs;

interface

  function GetIntCalcResult(const IntVal: Integer); 

implementation

  function GetIntCalcResult(const IntVal: Integer); stdcall; external 'HNLib.dll';

end.

// Your own app's code
program Test;

interface

  uses MyDllProcs;

implementation

function DoSomethingWithDll(const ValueToCalc: Integer): Integer;        
begin
  Result := GetIntCalcResult(ValueToCalc);
end;

begin
  WriteLn('DoSomethingWithDll returned ', DoSomethingWithDll(10));
  ReadLn;
end.

Note that when statically linking DLL functions like this, your DLL must be available when your app starts, and the function must be contained in that DLL; if not, your application won’t load.

Also, note that you can’t typically have multiple functions with the same name in the DLL, as there’s no information available to use to figure which one to load when the load is being done. Each should have a separate, distinct name or the loading will probably fail.