On 2 January 2016 at 11:42, Jonathan Wakely wrote: > On 31 December 2015 at 18:49, James Dennett <james.denn...@gmail.com> wrote: >> On Thu, Dec 31, 2015 at 4:42 AM, Jonathan Wakely <jwakely....@gmail.com> >> wrote: >>> >>> On 31 December 2015 at 11:54, Dominik Vogt wrote: >>> > Is there a requirement for a certain minimum Glibc version for >>> > this to work? >>> >>> It doesn't work with any glibc, because it doesn't declare the C++ >>> overloads. >>> >>> Libstdc++ has an include/c_compatibility/math.h header that would >>> include <cmath> (which declares the C++ overloads) and then pull them >>> into the global namespace, but that isn't used on GNU/Linux, and would >>> create other problems. >>> >> >> What other problems? >> >> It's something of an assumption of the C++ Standard that it's practical for >> C++ implementations to provide such wrappers to add overloads for C++. If >> that's causing some fundamental problem then we should document it (and >> ideally address it). > > Not fundamental problems in the standard, just with the implementation > of that header. It won't work as is and would need changes
Specifically, that header assumes that <cmath> is include/c/cmath, but for GNU/Linux we use include/c_global/cmath, and IIUC it assumes that the libc header defines some of the C++ overloads (but not all?), which isn't true for glibc. So the combination of include/c/cmath and include/c_compatibility/math.h wouldn't work. We could change it to work, but that might break targets using those headers already (possibly just QNX? I don't know). If we want to fix it in libstdc++ then I think we need a different math.h, written from scratch, not starting from include/c+compatibility/math.h
