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Subject: Re: [boost] cygwin API: posix or windows
From: Vladimir Prus (vladimir_at_[hidden])
Date: 2011-01-08 05:08:47

Beman Dawes wrote:

> On Thu, Jan 6, 2011 at 4:32 PM, vicente.botet <vicente.botet_at_[hidden]> wrote:
>> Hi,
>> while trying to make Boost.System and Boost.Chrono configurable header only libs we need to
>> include windows.h on some include files. To avoid the inclusion of this intrusive file, we
>> decided sometime ago to include some files in detail/win that will present just the needed
>> interfaces.
>> In my humble opinion cygwin is a wrapper of posix intefaces under windows OS.
> Cygwin is a distribution, not an API. The Cygwin distribution includes
> both the POSIX API and, via MinGW, the Windows API.

There are different opinions of what cygwin really means. Where I am, most folks
believe that Cygwin is a flavour of GNU operating system, which happens to use
Windows kernel somewhere deep inside, and provides POSIX API. Also, where I am,
most folks are scared of that strange creature.

> <aside> The POSIX API is implemented by calling the Windows API, so is
> really only an emulation of POSIX. It does a great job, but is weak in
> a few areas, such as permissions, where the Windows API doesn't allow
> 100% emulation of POSIX. </aside>
>> So, boost libraries shouldn't use Windows interfaces when working under cygwin.
> That doesn't follow. A primary use of Cygwin is simply to gain access
> to GCC on Windows, without any intent to ever port code to POSIX
> systems, and without any interest in, or knowledge of, the POSIX API.

I think you'd just use mingw for that? Which is smaller for starters.
Cygwin is only sensible if you actually want GNU operating system, including
your familiar (ba)sh prompt, and a pack of various command-line tools.

> This use has become more popular as GCC has jumped far ahead of VC++
> in terms of C++0x support.
> Another primary use of Cygwin is to gain access to GCC and the POSIX
> API on Windows, but that doesn't imply anything about what Boost
> implementations should do.
>> What's the experience of others?
> Boost.Filesystem V2 implementation code provided an option on Windows
> of compiling under GCC using the POSIX API. It was difficult to test,
> rarely worked well, was a source of confusion, and wasted too much of
> my time. So Filesystem V3 and Boost.System dropped any pretense of
> compiling with the POSIX API on Windows. There have been no complaints
> so far.
> Boost.System only uses a very few O/S API calls, so it would be
> relatively easy to compile for the Cygwin supplied POSIX API on
> Windows. But there have been no requests, so far.

I don't have any comments about whether it's worthwhile for any
specific library to support cygwin-the-api, but I would really
suggest to treat Cygwin as a different operating system, and entirely
forget there's Windows somewhere beyond.

- Volodya

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