Implicit linking vs. explicit linking of DLL in Delphi

Question

I'm having trouble getting my dll to work when using explicit linking. Using implicit linking it works fine. Would someone google me a solution? :) No, just kidding, here's my code:

This code works fine:

function CountChars(_s: Pchar): integer; StdCall; external 'sample_dll.dll';

procedure TForm1.Button1Click(Sender: TObject);
begin   
  ShowMessage(IntToStr(CountChars('Hello world')));
end;

This code doesn't work (I get an access violation):

procedure TForm1.Button1Click(Sender: TObject);
var
  LibHandle: HMODULE;
  CountChars: function(_s: PChar): integer;
begin

  LibHandle := LoadLibrary('sample_dll.dll');
  ShowMessage(IntToStr(CountChars('Hello world'))); // Access violation
  FreeLibrary(LibHandle);
end;

This is the DLL code:

library sample_dll;

uses
  FastMM4, FastMM4Messages, SysUtils, Classes;

{$R *.res}

function CountChars(_s: PChar): integer; stdcall;
begin
  Result := Length(_s);
end;

exports
  CountChars;

begin  
end.

Answer 1

procedure TForm1.Button1Click(Sender: TObject); 
var 
  LibHandle: HMODULE; 
  CountChars: function(_s: PChar): integer;

In above line you have missed StdCall modifier.

Answer 2

procedure TForm1.Button1Click(Sender: TObject);
var
  LibHandle: HMODULE;
  CountChars: function(_s: PChar): integer; stdcall; // don't forget the calling convention
begin
  LibHandle := LoadLibrary('sample_dll.dll');
  if LibHandle = 0 then
    RaiseLastOSError;
  try
    CountChars := GetProcAddress(LibHandle, 'CountChars'); // get the exported function address
    if not Assigned(@CountChars) then
      RaiseLastOSError;

    ShowMessage(IntToStr(CountChars('Hello world')));
  finally
    FreeLibrary(LibHandle);
  end;
end;

Answer 3

See also http://www.drbob42.com/examines/examinC1.htm for a third solution, available in Delphi 2010, the Delayed loading of Dynamic Link Libraries...