RE: [Mingw-users] Call Mingw DLL from a Visual Basic application

[Anand, V. R <vai...@bo...>]

Ted:
Why would you want to use the Cygwin compiler at all ? If you have
installed the MinGW package, then I would suggest that you use the MinGW
compiler instead. Let's say you have functions func1.c,func2.c. Then you
simply do the following (as per Mumit Khan's procedure):
gcc -c  -DBUILDING_DLL=3D1 -mrtd -g -O2 func1.c
gcc -c  -DBUILDING_DLL=3D1 -mrtd -g -O2 func2.c
dllwrap -s --export-all --output-def myfuncs.def --driver-name gcc -o
myfuncs.dll func1.o func2.o
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The resulting DLL should be usable from VB. I have done just this to
create DLL's that can be called from MS Excel inside a VB macro and the
DLL works just fine, provided you declare the DLL functions correctly
(return value and arguments) inside the macro using the Declare
statement. Further, this approach works for DLL's created from both C
and Fortran code; I was able to take the fftpack package from the Netlib
collection and easily build it into an Excel-callable DLL and
successfully use it inside VB. The only thing you have to be careful
about is sending/receiving pointer-based data from the DLL. While this
is easily handled in C, de-referencing pointers in VB is slightly
roundabout and involves using the "RtlMoveMemory" function from
kernel32.dll (it does the same job as memcpy()) and possibly the
VarPtr() function inside VB. VB wasn't designed to allow easy pointer
manipulation! Hope this helps.
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Regards,
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Anand

	-----Original Message-----
	From: Unnikumaran, Ted [mailto:ted...@mi...]=20
	Sent: Wednesday, June 02, 2004 3:03 PM
	To: min...@li...
	Subject: [Mingw-users] Call Mingw DLL from a Visual Basic
application
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	My goal is to create a dll created in mingw that I can call from
a Visual Basic application.  The code was initially written on a Linux
box and I'm trying to get it to work on Windows.  It compiles in cygwin,
but I would like to create a Visual Basic front end.

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	What I first did was the following:

	$gcc -shared -mrtd -mno-cygwin -o foo.dll foo.c

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	I was able to get foo.dll to work.  However, I had problems
using the -mno-cygwin flag when I tried to compile other components.

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	I read what Mumit Khan suggested and added his files to
/usr/local/mingw, and then tried to compile again with "-mno-cygwin"
flag with the -I/usr/local/mingw/include and the -L/usr/local/mingw/lib
options.  However, this still failed to fully compile.

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	I then installed mingw into c:/mingw and followed the directions
in the FAQ - "How do I use MinGW with Cygwin?"

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	However, I'm not too sure what options to give my gcc compiler.
Do I just get rid of the -mno-cygwin flag?  I tried that and the
simplest case of foo.dll now doesn't work.  It compiles, but when I try
to use it from the VB application, it crashes.

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	I then tried to follow the directions in the FAQ "How can an
MSVC program call a MinGW DLL, and vice versa?"

	What I did was run the following commands:

	$gcc -shared -o foo.dll foo.c
-Wl,--output-def,foo.def,--out-implib,libfoo.a

	$lib /machine:i386 /def:foo.def

	$cl foo.c foo.lib

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	This creates the file foo.exe and foo.obj.  The exe works, and I
can execute it from the command line.  However, I want a dll that I can
call from a VB program.  The dll that is created using the above 3 steps
depends on cygwin1.dll, and even with it doesn't seem to work, as it
crashes my VB program.

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	Any suggestions would be appreciated.

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	Thanks,

	Ted

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