Calling a Delphi generated DLL fails to load in Matlab

I have a dll created in Delphi XE2 which I would like to use in Matlab, but fails to load with loadlibrary. To simplify the problem a very basic dll has been created to test whether it works at all. When loading the simple library the dll cannot be loaded because it is not a valid Win32 application, although it is compiled for Win32 in Delphi. What is causing this?

>> loadlibrary('C:\Users\Me\Documents\Matlab\TestAPI.dll','C:\Users\Me\Documents\Matlab\TestAPI.h','alias','testapi')
Error using loadlibrary (line 421)
There was an error loading the library
"C:\Users\Me\Documents\MATLAB\TestAPI.dll"
C:\Users\Me\Documents\MATLAB\TestAPI.dll is not a valid Win32 application.

Caused by:
    Error using loaddefinedlibrary
    C:\Users\Me\Documents\MATLAB\TestAPI.dll is not a valid Win32
    application.

The header file is:

#ifndef TESTAPI_DLL_H
#define TESTAPI_DLL_H

#ifdef __cplusplus
extern "C" {
#endif

#ifdef BUILDING_TESTAPI_DLL
#define TESTAPI_DLL __declspec(dllexport)
#else
#define TESTAPI_DLL __declspec(dllimport)
#endif

// ----------------------------------------------------------------------------
// Test procedure; shows messagebox
// ----------------------------------------------------------------------------
bool __stdcall DllMessage;

#ifdef __cplusplus
}
#endif

#endif // !defined(TESTAPI_DLL_H)

The TestAPI:

library TestAPI;

uses
  SysUtils,
  Classes,
  Dialogs;

{$R *.res}

function DllMessage: Boolean stdcall; export;
begin
  ShowMessage('Hello world from a Delphi DLL') ;
  Result:=true;
end;

exports
  DllMessage;

begin
end.

I'm using Delphi XE2 on windows 7 64 with Matlab R2011b.

Answer 1

[Kaustubha Govind]

It seems like your DLL might be 32-bit, which cannot be loaded on 64-bit MATLAB. Please see this previous discussion which was about the same issue.

[Oscar]

Thanks, I never realized that the Matlab version I'm using is a 64 bit application... Strange error by the way. As the dll is a correct 32 bit application I would have anticipated a message stating that the dll is not a valid 64 bit application to run in Matlab?

Installing the 32 bit Matlab version worked!

[Kaustubha Govind]

Oscar: I agree that "is not a valid Win32 application" is very non-intuitive - unfortunately, this is an error from the OS AFAIK. If you perform a web search for that phrase, you'll see that it's not limited to MATLAB, but is a Windows thing.