Re: boost program_options library with cygwin

[Brian Dessent <brian at dessent dot net>]

Thomas Porschberg wrote:

> because libcppunit was built as cygwin-library. I resolved the
> problem by compiling the library from sources with -mno-cygwin
> flag. And then I used this library for both, my application
> cygwin-build and my application mingw-build.
> If I understand you right, this is at least dangerous. I have

Yes, it's dangerous, and I'm surprised it works.

Basically, you have to treat Cygwin and mingw as two completely separate
platforms.  You'll have to compile two versions of your code and every
library that it links with.  In the case of the Cygwin version of the
library, you can use the copy installed by setup.exe from the Cygwin
mirrors.  But it is not a goal of the Cygwin project to provide packaged
versions of mingw libraries (except for a couple of common cases like
zlib) so don't expect to use any of the libraries found on a Cygwin
mirror when compiling for mingw.  You'll have to do this yourself, or
get them from the mingw site.

To do this sanely under Cygwin, it seems to me like you could do
something like the following (untested) for each package/library:

mkdir cygwin-build && cd cygwin-build
CC="gcc" ../configure --prefix=/usr/local/cygwin \
      CFLAGS="-I/usr/local/cygwin/include" \
      LDFLAGS="-L/usr/local/cygwin/lib" # etc..
make && make install
cd ..

mkdir mingw-build && cd mingw-build
CC="gcc -mno-cygwin" ../configure --prefix=/usr/local/mingw \
      CFLAGS="-I/usr/local/mingw/include" \
      LDFLAGS="-L/usr/local/mingw/lib" # etc..
make && make install

This keeps the separation between installed packages such that
everything installed under /usr/local/cygwin is Cygwin, and everything
installed under /usr/local/mingw is mingw.  The reason for not using
just /usr/local is that the compiler picks up libraries installed there
by default, so you wouldn't want it picking up a cygwin lib when
compiling in mingw mode, and so on.

You could also do it by using mounts.  Mount one /usr/local, do a Cygwin
compile and install of all packages, then unmount and remount a
different /usr/local and redo everything in mingw mode.

However you handle it, you have to keep this separation.  I would not
try to mix them under the same --prefix unless you really know what
you're doing.

You can even just forget about using -mno-cygwin and have an install of
Cygwin and an install of mingw+MSYS, and  treat them as if they have no
idea about each other, just as you would if you were supporting e.g.
Cygwin and MS VC++.

Also, it's important to realize that the -mno-cygwin flag is provided as
a convenience to turn the Cygwin build environment into mingw mode, but
the mingw project is an independant effort from Cygwin.  Porting mingw
applications is not really on-topic for this list.  If you have
questions about compiling with mingw you should ask on their mailing
list.

Brian

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