https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118173
Bug ID: 118173
Summary: reinterpret_cast<void(*)()> from const void* casts
away constness, but is accepted
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: janschultke at googlemail dot com
Target Milestone: ---
> const void* null = nullptr;
> auto n = reinterpret_cast<void(*)(void)>(null);
https://godbolt.org/z/Mbajjfn6n
GCC accepts this invalid code (as does MSVC); Clang rejects.
By definition in https://eel.is/c++draft/expr.const.cast#6, this code is
ill-formed because the conversion from 'const void*' to 'void(*)()' casts away
constness. https://eel.is/c++draft/expr.reinterpret.cast#2 disallows
reinterpret_cast from doing so.
While function types cannot be const-qualified anyway, there is no special rule
in the standard for them here, and this is dropping const as much as 'const
void*' -> 'void*'.
See standardese explanation here:
https://github.com/cplusplus/CWG/issues/657#issuecomment-2558598637
