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Subject:	Re: iostream doesn't work (clang++)
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	<47f9e50d-763b-e6a9-b2b0-8d3cc311a63b AT maxrnd DOT com>
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Date:	Fri, 7 Jul 2023 01:01:18 -0700
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From:	Mark Geisert via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Mark Geisert <mark AT maxrnd DOT com>
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Brian Inglis via Cygwin wrote:
> On 2023-07-05 09:54, ggl329 via Cygwin wrote:
>> Hi Mark,
>>
>> On 2023/07/05 12:06, Mark Geisert via Cygwin wrote:
>>> My previous reply addressed the specific error reported by your testcase.
>>> But I am unable to make progress on the root cause because I can't reproduce 
>>> your report.
>>
>> Hm, it seems to be difficult to track down the root cause...
>>
>>> On my system I try the compilation and see:
>>> ~ clang++ sample.cc
>>> sample.cc:1:10: fatal error: 'iostream' file not found
>>> #include <iostream>
>>>           ^~~~~~~~~~
>>> 1 error generated.
>>
>> I tried with clang++ --verbose, and the log showed search paths for #include.
>> iostream is at /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++/iostream.
>> Can you find it? It comes from gcc-g++.
>> Or the search path includes /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++?
> 
> Package clang pulls in headers and libraries from libc++-devel libclang8 
> libunwind-devel gcc-g++ libstdc++6 gcc-core cygwin-devel so the primary include 
> paths should be from:
> libc++-devel /usr/include/c++/v1/ for most language and library definitions and 
> libraries,
> libclang8 /usr/lib/clang/8.0.1/include/ for clang intrinsics and builtins,
> libunwind-devel /usr/include/ for exception handling definitions and libraries,
> gcc-g++ /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++/{x86_64-pc-cygwin/,} and 
> libstdc++6 for C++ system dependent and low level definitions and libraries,
> gcc-core /usr/lib/gcc/x86_64-pc-cygwin/11/include/ for system dependent and low 
> level intrinsics and interfaces, and
> cygwin-devel /usr/include/{*/,} for system dependent and low level definitions and 
> libraries.
> 
> Everything clang should be prioritized over anything gcc to prevent such issues, 
> so cygcheck -c clang llvm libc++-devel libclang8 libunwind-devel gcc-g++ 
> libstdc++6 gcc-core cygwin-devel to ensure eveything has been installed properly.
> 
> Unfortunately clang{,++,-cpp} -print-search-dirs does *NOT* show include paths,
> but -v and -### complain about nonexistent /usr/include/c++/11 where 
> /usr/include/c++/v1 exists!
> It appears the search list ignores the directories populated in libc++-devel:
> ... -resource-dir /usr/lib/clang/8.0.1
> -internal-isystem /usr/x86_64-pc-cygwin/include/c++
> -internal-isystem /usr/x86_64-pc-cygwin/include/c++/x86_64-pc-cygwin
> -internal-isystem /usr/x86_64-pc-cygwin/include/c++/backward
> -internal-isystem /usr/x86_64-pc-cygwin/include/c++/11
> -internal-isystem /usr/x86_64-pc-cygwin/include/c++/11/x86_64-pc-cygwin 
> -internal-isystem /usr/x86_64-pc-cygwin/include/c++/11/backward
> -internal-isystem /usr/include/c++/11
> -internal-isystem /usr/include/c++/11/x86_64-pc-cygwin
> -internal-isystem /usr/include/c++/11/backward
> -internal-isystem /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++
> -internal-isystem /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++/x86_64-pc-cygwin 
> -internal-isystem /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++/backward
> -internal-isystem /usr/lib/clang/8.0.1/include
> -internal-isystem /usr/local/include
> -internal-isystem /usr/lib/clang/8.0.1/include
> -internal-isystem /usr/x86_64-pc-cygwin/include
> -internal-isystem /usr/include
> -internal-isystem /usr/include/w32api ...
> ignoring nonexistent directory "/usr/x86_64-pc-cygwin/include/c++"
> ignoring nonexistent directory "/usr/x86_64-pc-cygwin/include/c++/x86_64-pc-cygwin"
> ignoring nonexistent directory "/usr/x86_64-pc-cygwin/include/c++/backward"
> ignoring nonexistent directory "/usr/x86_64-pc-cygwin/include/c++/11"
> ignoring nonexistent directory 
> "/usr/x86_64-pc-cygwin/include/c++/11/x86_64-pc-cygwin"
> ignoring nonexistent directory "/usr/x86_64-pc-cygwin/include/c++/11/backward"
> ignoring nonexistent directory "/usr/include/c++/11"
> ignoring nonexistent directory "/usr/include/c++/11/x86_64-pc-cygwin"
> ignoring nonexistent directory "/usr/include/c++/11/backward"
> ignoring nonexistent directory "/usr/x86_64-pc-cygwin/include"
> ignoring duplicate directory "/usr/lib/clang/8.0.1/include"
> #include "..." search starts here:
> #include <...> search starts here:
>   /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++
>   /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++/x86_64-pc-cygwin
>   /usr/lib/gcc/x86_64-pc-cygwin/11/include/c++/backward
>   /usr/lib/clang/8.0.1/include
>   /usr/local/include
>   /usr/include
>   /usr/include/w32api
> End of search list.
> 
> You may want to try to override the built in includes from -internal-isystem with 
> those mentioned above but not built in.
> 
> I have no idea why both compilers would include w32api headers as if they were 
> building Mingw cross compilers!

Thanks very much Brian for this overview.  I'd rather not delay a fix for the OP 
any longer, so I have submitted a patch for the reported issue.  If it turns out 
that, with the patch, the OP can successfully compile and build his testcase, we 
may be done.

If not, somebody (TM) may have to dig into what's been discovered and how to 
remedy it.  Comparing Cygwin's clang/clang++ installation with some Linux's 
installation might be helpful.  I have some other ideas but I can't commit time to 
following them up ATM.
Thanks all,

..mark

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