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From: Martin Henne <martin DOT henne AT web DOT de>
To: cygwin AT cygwin DOT com
Subject: build DLL that can be used by MinGW
Date: Mon, 8 Feb 2010 09:50:14 +0100
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Hello,

I try to produce a DLL on cygwin, that can be linked against a MinGW compiled 
program. To test with a simple example I tried the following code:

// dllfunc.h
extern "C" {
  extern void sayhello();
  extern int sumint(int a, int b);
}

// dllfunc.cpp
#include <iostream>
extern "C" {
  void sayhello() {
    std::cout << "I am saying hello" << std::endl;
  }
  int sumint(int a, int b) {
    return a+b;
  }
}

// main.cpp
#include <iostream>
#include "dllfunc.h"
int main() {
  std::cout << "1" << std::endl;
  std::cout << sumint(3,39) << std::endl;
  std::cout << "2" << std::endl;
  sayhello();
  std::cout << "3" << std::endl;
}

Then I created the dll (within cygwin):
$> g++ -shared dllfunc.cpp -o dllfunc.dll

Then I created the application (using MinGW)
$> g++ main.cpp -L. -ldllfunc

When I start this MinGW-Application, the call output is as follows:

1
42
2

Then it aborts. That means, that the call to 'sumint()' whithin the
dll works, while the call to 'sayhello()' wont. The crash occurs when using
'std::cout'.

If I compile and create the dll and the application within cygwin it works:
1
42
2
I am saying hello
3

If I compile both using MinGW it works, too.
If I compile the DLL on MinGW and the application on cygwin, it works as well.

But I need to compile the DLL on cygwin and the rest on MinGW, and this does
not work. The reason is, that I need a dll that uses the cygwin-posix-layer.

What can I do?

Thank you in advance...



Martin


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