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Date: Wed, 3 Nov 2004 16:30:02 -0500 (EST)
From: Igor Pechtchanski <pechtcha AT cs DOT nyu DOT edu>
Reply-To: cygwin AT cygwin DOT com
To: rene DOT nyffenegger AT adp-gmbh DOT ch
cc: cygwin AT cygwin DOT com
Subject: Re: creating shared object (.so) with gcc under cygwin
In-Reply-To: <20041103171139.M29773@adp-gmbh.ch>
Message-ID: <Pine.GSO.4.61.0411031622560.27136@slinky.cs.nyu.edu>
References: <20041103171139 DOT M29773 AT adp-gmbh DOT ch>
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On Wed, 3 Nov 2004, Rene Nyffenegger wrote:

> Hello
>
> I am trying to create a shared object and use it in a program under
> cygwin with gcc. I seem to miss a point. If some kind soul could help
> me on that, I'd be very grateful.
>
> Here's the code for the shared object (calc_mean.c):
>
>   #include "calc_mean.h"
>   double mean(double a, double b) {
>     return (a+b) / 2;
>   }
>
> Here's its header file (calc_mean.h):
>
>   double mean(double, double);
>
>
> So, I compile that to a .so like so:
>
> $ gcc -shared -o libmean.so calc_mean.c
>
> Then, there's main.c that wants to use the shared object:
>
>   #include <stdio.h>
>   #include "calc_mean.h"
>
>   int main(int argc, char* argv[]) {
>     double v1, v2, m;
>     v1 = 5.2;
>     v2 = 7.9;
>
>     m  = mean(v1, v2);
>
>     printf("The mean of %3.2f and %3.2f is %3.2f\n", v1, v2, m);
>     return 0;
>   }
>
> I try to compile main.c like so:
>
> $ gcc main.c -o main -L. -lmean
>
> However, the following error is returned:
> /usr/lib/gcc-lib/i686-pc-cygwin/3.3.3/../../../../i686-pc-cygwin/bin/ld:
> cannot find -lmean
> collect2: ld returned 1 exit status
>
> Obviously, I do something wrong here, but I have no idea what that could
> be.

As Chris recommended, use the ".dll" extension for your shared libs, or
you can also build an import lib using

$ gcc -shared -o libmean.so -Wl,--out-implib,libmean.dll.a calc_mean.c

and your link step should work.
	Igor
-- 
				http://cs.nyu.edu/~pechtcha/
      |\      _,,,---,,_		pechtcha AT cs DOT nyu DOT edu
ZZZzz /,`.-'`'    -.  ;-;;,_		igor AT watson DOT ibm DOT com
     |,4-  ) )-,_. ,\ (  `'-'		Igor Pechtchanski, Ph.D.
    '---''(_/--'  `-'\_) fL	a.k.a JaguaR-R-R-r-r-r-.-.-.  Meow!

"The Sun will pass between the Earth and the Moon tonight for a total
Lunar eclipse..." -- WCBS Radio Newsbrief, Oct 27 2004, 12:01 pm EDT

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