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X-HELO:	mga12.intel.com
From:	"Soegtrop, Michael" <michael DOT soegtrop AT intel DOT com>
To:	Agner Fog <agner AT agner DOT org>, "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject:	RE: Why is __unix__ defined, and not __WINDOWS__ ?
Date:	Mon, 13 May 2019 07:54:23 +0000
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Dear Agner,

> But the compiler generates a Windows executable following most of the
> Windows ABI (object file format, calling convention, etc.)

Still cygwin is intentionally very different from Windows, e.g. on Cygwin you use / as path separator, on Windows you use \ as path separator. Cygwin console executables produce \n line endings, MinGW produce \r\n line endings. Cygwin executables go through path translation (C:\ is /cygdrive/c/) ... Many C programs will consult __WINDOWS__ to find out what the path separator should be and this would go wrong if cygwin gcc would define __WINDOWS__. I would see Cygwin as a lightweight Posix virtual environment on Windows. If you run gcc on the Linux Subsystem for Windows you also wouldn't expect it to define __WINDOWS__. In a sense the reason Cygwin exists is that it has a gcc which defined __unix__.

As was mentioned before, if you goal is to create Windows ABI compatible binaries, you should use the MinGW cross compiler, which is available as package for Cygwin (mingw64-x86_64-... ). Please note that you should use a 64 bit cygwin to create 64 bit binaries and a 32 bit Cygwin to create 32 bit binaries. This is because the Windows filesystem has a hack that 32 and 64 bit DLLs have the same filename and which one you get depends on if you are a 32 bit or 64 bit executable. So 64 bit linker which is a 32 bit executable trying to create a 64 bit binary would see the wrong DLLs and vice versa.

Another option is to use a MinGW, MSys or MSys2 distribution - I personally prefer Cygwin exactly because it does this stricter separation between a Posix world and a Windows world. But if you main goal is to have a gcc for Windows, Cygwin might not be the best choice for you.

Best regards,

Michael
Intel Deutschland GmbH
Registered Address: Am Campeon 10-12, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de
Managing Directors: Christin Eisenschmid, Gary Kershaw
Chairperson of the Supervisory Board: Nicole Lau
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Commercial Register: Amtsgericht Muenchen HRB 186928

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