Subj : Help with DLL, some additional questions.
To   : borland.public.cpp.borlandcpp
From : tazzi
Date : Sat Nov 20 2004 06:25 pm

Ed:

I have had some success and some additional questions.
This dialog continues from an earlier question,
which was incorrectly posted at
newsgroups.borland.com/borland.public.cppbuilder
for those interested in following the entire thread.

Using the first bit of code that you supplied,
I performed 3 experiments.  The code is listed below:

Code:
-------------------------------------------------
#include <windows.h>

#ifdef __BORLANDC__
#pragma argsused 
#endif

BOOL WINAPI DllEntryPoint(
  HINSTANCE dllInst, DWORD reason, LPVOID i)
  {
  return TRUE;
  }

__declspec(dllexport)

int __stdcall mult(int a, int b)
{
 return a*b;
}
--------------------------------------------------

Experiment #1: 
1. From IDE, compile mult.c to mult.dll.
 -> This produces the file mult.dll which
    is 6.5kb long.
2. Start Maple and attempt to load with
   the following command:
 
 > mult :=
 > define_external('mult',
 > a::integer[4],
 > b::integer[4],
 > LIB="mult.dll",
 > RETURN::integer[4]):
 
-> Produces a failed load, with the following
error message:

"Error, external lookup of mult: The specified
procedure could not be found."  

Experiment #2: 
1. From command line, compile mult.c to mult.dll
using the following command (Note: Must kill Maple 
session, as the program has opened "mult.dll" and
this file can not be deleted):

bcc32 -WD mult.c
-> This produces the file mult.dll which
   is 56kb long.
2. Start Maple and attempt to load with
   previous command.
   
-> Produces a successful load!  
3. Now test the DLL:

 > mult(2,3); ->  6 (Correct answer)   
 
Experiment #3: 
1. Copy mult.c to mult.cpp (the original extension used
in my first correspondence).  From command line, compile 
mult.cpp to mult.dll using the following command:

bcc32 -WD mult.cpp
-> This produces the file mult.dll which
   is 56kb long.
2. Start Maple and attempt to load with
   previous command.

-> Produces a failed load, with the following
error message:

"Error, external lookup of mult: The specified
procedure could not be found."  
---------------------------------------------
Ed, can you answer the following questions?

1. Returning to you previous answer, I don't 
understand where I would use second bit of 
code that you supplied:

Code:
----------------------------------------------
#ifndef SOMEDLL_H
#define SOMEDLL_H

/* handle if this C function is used from C++ */
#ifdef __cplusplus
extern "C"
#endif

__declspec(dllimport) int __stdcall mult(int, int);

#endif
----------------------------------------------

2. Can you explain what settings I need to 
make in the IDE to get it to compile correctly,
as with the command line experiment #2?

3. When the code has a cpp extension, does
the compiler change the function names?
This may be why experiment #3 failed.

Thanks,
tazzi

.