[racket] Access c based dll through ffi

At Wed, 13 Feb 2013 11:08:08 +0100, heraklea at gmx.de wrote:
> Hello Friends,
> 
> I have make a little dll in visual studio :
> [CODE_BEGIN]
> #include <stdio.h>
> 
> extern "C"
> {
>   __declspec(dllexport) void DisplayHelloFromDLL()
>   {
>     printf ("Hello from DLL !\n");
>   }
> }
> [CODE_END]
> 
> After I try to access it through ffi like this:
> [CODE_BEGIN]
> #lang racket
> 
> (require ffi/com
>          ffi/unsafe
>          ffi/unsafe/define
>          ffi/winapi
>          racket/string
>          racket/format)
> 
> (define-ffi-definer define-dreamlog (ffi-lib "DreamLogging"))
> [CODE_END]
> 
> 
> But I get an 
> ffi-lib: couldn't open "DreamLogging.dll" (Unknown error; errno=193)

Error code 193 is "bad exe format". Are your DLL and Racket both 32-bit
or both 64-bit?

(The text of the error message says "Unknown error" because the
system-provided error text has a formatting command in it. I can make
Racket show the error text with the formatting command, which will be
ugly but more useful than showing only the error code.)