problem with delphi dll when called from another delphi app

Hi!

In your project, you must add ShareMem (as first entry) in your project uses line.

Project->View source and add ShareMem in the uses:

program Project1;

uses
  ShareMem,
  Forms,
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

begin
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

This is because you are using strings in a exported function of a DLL.

Ah!, the DLL declaration is wrong in your example, is a function, not a procedure, and the uses line of the DLL has innecesary parts.

Here is my sources:

The DLL:

library thenewdll;

{ Important note about DLL memory management: ShareMem must be the
  first unit in your library's USES clause AND your project's (select
  Project-View Source) USES clause if your DLL exports any procedures or
  functions that pass strings as parameters or function results. This
  applies to all strings passed to and from your DLL--even those that
  are nested in records and classes. ShareMem is the interface unit to
  the BORLNDMM.DLL shared memory manager, which must be deployed along
  with your DLL. To avoid using BORLNDMM.DLL, pass string information
  using PChar or ShortString parameters. }

uses
  ShareMem,
  Windows,
  SysUtils;

{$R *.res}

function  gettotalmem():string;

var
GlobalMemoryInfo: TMemoryStatus; // holds the global memory status information
begin
   {set the size of the structure before the call}
  GlobalMemoryInfo.dwLength := SizeOf(GlobalMemoryInfo);

  {retrieve the global memory status...}
  GlobalMemoryStatus(GlobalMemoryInfo);

    {and display the information}

  gettotalmem := IntToStr(GlobalMemoryInfo.dwTotalPhys);

end;


  exports gettotalmem;
end.



The caller project:

Unit1:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;


function gettotalmem: string; external 'thenewdll.dll'  

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  x: string;
begin
    x:=gettotalmem;
    showmessage(x);
end;

end.

The project source:

program Project1;

uses
  ShareMem,
  Forms,
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

begin
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.