[[ CC += libc-coord at lists.openwall.com ]]
On 2020-09-21 12:33, Florian Weimer wrote:
* Alejandro Colomar:
[[
CC += libc-coord at sourceware.org
CC += gcc at gcc.gnu.org
CC += libstdc++ at gcc.gnu.org
]]
Hi Florian,
On 2020-09-21 10:38, Florian Weimer wrote:
* Alejandro Colomar via Libc-alpha:
I'd like to propose exposing the macro 'array_length()' as defined in
'include/array_length.h' to the user.
It would need a good C++ port, probably one for C++98 and another one
for C++14 or later.
For C++, I use the following definition:
#include <cassert>
#include <sys/cdefs.h>
#include <type_traits>
#define is_array__(a) (std::is_array <__typeof__(a)>::value)
Should be decltype.
Thanks.
However, there are a few problems:
1) This doesn't work for VLAs (GNU extension).
I couldn't find a way to do it. Maybe I should file a bug in GCC.
I do not think VLA support is critical. C++ programmers will be used to
limited support in utility functions.
2) Also, this requires C++11; I don't know how to do it for older C++.
Again, support from the compiler would be great.
I think limited C++98 support is possible using a function template,
where the array length N is a template parameter. To enable use in
constant expressions, you can return a type of char[N], and the macro
wrapper should then apply sizeof to the function result.
Sorry, I don't know much C++, and I don't know how to do this.
3) The macro can't be used in the same places as the C version,
because of the `({})`.
The `0 * sizeof(struct{...})` trick doesn't work in C++ due to:
error: types may not be defined in 'sizeof' expressions
For C++11, you can use a constexpr function instead of a macro.
array_length should not be a macro in current C++ modes, so that we
retain compatibility if a future C++ standard adds array_length (or
nitems) on its own. This is not a concern for legacy C++98 mode.
See above.
Maybe also ask on the libc-coord list.
Ok. Added CCs.
libc-coord is not hosted on sourceware:
<https://www.openwall.com/lists/libc-coord/2020/01/30/1>
The discussion here veered off into C++ territory anyway.
I added the correct list now.
Thanks,
Florian
Thanks,
Alex.
