On 28/05/2020 23:01, Xavier Del Campo Romero via Gcc wrote:
Hello gcc team,
I have sent the following proposals to the committee, but they require them to
be implemented at least into two major compilers, so I am proposing them to be
implemented into gcc. This is going to be a rather lengthy e-mail, so TL;DR:
Proposal 1: New pointer-proof keyword _Lengthof to determine array length
Motivation: solve silent bugs when a pointer is accidentally used instead of an
array
In gcc, the simple "#define ARRAY_SIZE(a) sizeof (a) / sizeof *(a)"
gives a compile-time warning if passed a pointer, since the introduction
of "-Wsizeof-pointer-div" in -Wall in gcc 8.
I am not convinced that anyone who would be careful enough in their
coding to use such a new "_Lengthof" feature would not already be using
"-Wall" at least. So for gcc, the new keyword would, I think, be
useless. And for any compiler without an equivalent warning (clang has
it from version 7), it would likely to be easier to add the warning
rather than the keyword.
Many people have figured out alternative "ARRAY_SIZE" macros that work
with existing compilers and give compile-time warnings on naked
pointers. But like your suggestion below, they rely on compiler
extensions such as gcc's "typeof".
So my counter-proposal for you would be to recommend gcc's "typeof" as a
new keyword (spelt "_Typeof", with "typeof" as a macro in <stdtypeof.h>,
in solid C tradition).
Then you have a feature that has a long-established history in two major
compilers (gcc and clang, at least), has been massively used in
real-world code for decades, and has a huge range of useful use-cases.
Get "typeof" into the C standards and many people will thank you! And
then your _Lengthof becomes a simple macro that can be put in a standard
header file, and needs no established implementation to be acceptable.
(And you don't need any help from gcc or clang, except perhaps for
describing the details of the semantics of "typeof".)
