On 23 September 2024 14:45:21 BST, Frederick Virchanza Gotham via Std-Proposals <std-proposals_at_[hidden]> wrote:
>On Mon, Sep 23, 2024 at 11:55 AM Gašper Ažman wote:
>>
>> HASH DOES NOT WORK. There are reasons for this in
>> this thread, but they boil down to this: you'd need to hash
>> the entire reachable filesystem because #include's don't
>> resolve the same way depending on where the file is accessed
>> from on the filesystem.
>>
>> #pragma once
>> #include "utils.h"
>>
>> You'll see that header verbatim several times for different libraries
>> in a translation unit and you'll miscompile. HASH DOES NOT WORK.
>
>
>Giving consideration to your above sample header file which I'll call
>"monkey.hpp", let's do it the other way:
>
> #ifndef HPP_MONKEY
> #define HPP_MONKEY
> # include "utils.h"
> #endif
>
>The problem here is that another library might also have a file named
>"monkey.hpp" and it might also use the same macro name "HPP_MONKEY" or
>"H_MONKEY" or "MONKEY_HPP". So really we want to do our inclusion
>guards something like:
>
> #ifndef HPP_MONKEY_239875623987523075623098765
> #define HPP_MONKEY_239875623987523075623098765
> # include "utils.h"
> #endif
>
>Stick a nice long random number in there.

Might as well just ditch the HPP_MONKEY part at this point, it serves no purpose.