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From:	svoboda AT cs DOT cmu DOT edu
Reply-To:	svoboda AT cs DOT cmu DOT edu
To:	cygwin AT sourceware DOT org
Subject:	Building DLL's using g++, not gcc
Date:	Mon, 17 Jan 2005 17:46:25 -0500
User-Agent:	KMail/1.7.2
Cc:	David Svoboda <svoboda AT cs DOT cmu DOT edu>
MIME-Version:	1.0
Message-Id:	<200501171746.26708.svoboda@cs.cmu.edu>
Source-Info:	Sender is really svoboda+@mandal.lti.cs.cmu.edu

I've been trying to build a DLL using g++, and given the problems I was 
having, I decided to try a 'toy' example, which is available at:
	http://cygwin.com/cygwin-ug-net/dll.html
I tweaked the two files around thusly:


hello.C:
-----
#include <stdio.h>
int hello() { printf("Hello World\n");}
-----

main.C:
-----
#include <stdio.h>
typedef void (*fn_type)();

extern "C" {
  int dlopen(char*);
  int dlsym( int, char*);
}

int main() {
  int handle = 0;
  fn_type fn = 0;
  if ((handle = dlopen( "hello.dll")) == 0) {
    printf( "Cannot open hello.dll\n");
  }
  if ((fn = (fn_type) dlsym( handle, "hello")) == 0) {
    printf( "Cannot open hello()\n");
  }
  fn();
}
-----

This way, hello.C is a valid C or C++ application, and main.C is a
valid C++ application. I build main.exe by:

	g++ -o main main.C

If I build hello.dll this way, it works:

	gcc -shared -o hello.dll hello.C
	./main
	Hello world!

But if I build hello.dll this way, it doesn't work:

	g++ -shared -o hello.dll hello.C
	./main
	bash: [2084: 2] testaddr: Inappropriate ioctl for device

Why? What am I doing wrong?

~David Svoboda


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