Using libcxx with musl's math.h

Using libcxx with musl's math.h

[Jeroen Ketema]

Hello,

I'm trying to use libcxx's cmath header together with musl's math.h. 
However this currently fails, because libcxx expects certain symbols to 
be functions, while musl defines them as macros. For example (compiling 
with clang):

cmath:309:9: error: no member named 'signbit' in the global
       namespace; did you mean '__signbit'?
using ::signbit;
       ~~^

where signbit is a macro in musl, but where libcxx expects it to be a 
function.

My question is: what would be the proper way to fix this? The main issue 
being of course that I cannot simply define signbit to be a function, 
because it requires a form of overloading.

Thanks,

  Jeroen

Re: Using libcxx with musl's math.h

[Rich Felker]

On Thu, Mar 10, 2016 at 06:46:12PM +0000, Jeroen Ketema wrote:
> Hello,
> 
> I'm trying to use libcxx's cmath header together with musl's math.h.
> However this currently fails, because libcxx expects certain symbols
> to be functions, while musl defines them as macros. For example
> (compiling with clang):
> 
> cmath:309:9: error: no member named 'signbit' in the global
>       namespace; did you mean '__signbit'?
> using ::signbit;
>       ~~^
> 
> where signbit is a macro in musl, but where libcxx expects it to be
> a function.
> 
> My question is: what would be the proper way to fix this? The main
> issue being of course that I cannot simply define signbit to be a
> function, because it requires a form of overloading.

I think this is a libcxx bug. C requires signbit to be a macro. If C++
has different requirements then the C++ implementation should be
providing an overlay header that satisfies them.

Rich

Re: Using libcxx with musl's math.h

[Jeroen Ketema]

Hi Rich,

Thanks for your quick answer.

Digging a bit deeper, it turns out that libcxx comes with it’s own math.h, which uses #include_next to include the C library's math.h. I totally missed this the first time through libcxx’s headers. Sorry for the noise.

Best,

 Jeroen

> On 10 Mar 2016, at 19:13, Rich Felker <dalias@libc.org> wrote:
> 
> On Thu, Mar 10, 2016 at 06:46:12PM +0000, Jeroen Ketema wrote:
>> Hello,
>> 
>> I'm trying to use libcxx's cmath header together with musl's math.h.
>> However this currently fails, because libcxx expects certain symbols
>> to be functions, while musl defines them as macros. For example
>> (compiling with clang):
>> 
>> cmath:309:9: error: no member named 'signbit' in the global
>>      namespace; did you mean '__signbit'?
>> using ::signbit;
>>      ~~^
>> 
>> where signbit is a macro in musl, but where libcxx expects it to be
>> a function.
>> 
>> My question is: what would be the proper way to fix this? The main
>> issue being of course that I cannot simply define signbit to be a
>> function, because it requires a form of overloading.
> 
> I think this is a libcxx bug. C requires signbit to be a macro. If C++
> has different requirements then the C++ implementation should be
> providing an overlay header that satisfies them.
> 
> Rich