[libcxx-dev] LLVM libcxx "hash" clashes with custom define "hash"

Marshall Clow via libcxx-dev libcxx-dev at lists.llvm.org
Wed Jul 29 06:13:46 PDT 2020

On Jul 29, 2020, at 5:32 AM, Oliver Major via libcxx-dev <libcxx-dev at lists.llvm.org> wrote:
> Hello everyone,
> I am new here and in fact not subscribed, I just have a question and don't even know if I am at the right address.
> We recently found a bug in our product code when building with NDK Clang for Android and it is related to the LLVM libcxx. It is fairly easy to reproduce and a quick internet search reveals that we are not the only ones with this or a similar issue.
> What we did, was
> #define hash #
> before
> #include <math.h>
> which let to a problem with libcxx/include/type_traits:417  
> template <class _Tp> struct _LIBCPP_TEMPLATE_VIS hash; 
> of course. We obviously shouldn't let defines leak into the stdlib, so it is our fault, we fixed it simply by renaming the define.


> I didn't want to post it as a bug in the LLVM bugtracker, because I don't even think it needs fixing on LLVM side. I just wanted to make aware that this issue exists for some people and wanted to ask if there is a way to publicly document this issue somewhere, so people having problems with this can potentially find a solution on the internet.

You’re not allowed to #define names that are defined in the standard library..
See http://eel.is/c++draft/macro.names <http://eel.is/c++draft/macro.names>, which states:

A translation unit that includes a standard library header shall not #define or #undef names declared in any standard library header.

— Marshall
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/libcxx-dev/attachments/20200729/88f78ec4/attachment-0001.html>

More information about the libcxx-dev mailing list