Most of these are pretty familiar if old enough but this is a wonderful list.
I didn’t know C23 was getting rid of trigraphs. That’s probably a good thing and easy to clean up if needed.
I didn’t know C23 was getting rid of trigraphs. That’s probably a good thing and easy to clean up if needed.
The stock verbiage about how modern compilers ignore "register" because they can do better but it may be useful on simpler ones, has been around in this exact form 20 years ago already. And one curious thing is that even back then, such statements would never list specific compilers where "register" still did something useful.
So far as I can tell, "register" was in actual use back when many C compilers were still single-pass, or at least didn't have a full-fledged AST, and thus their ability to do things like escape analysis was limited. With that in mind, "register" was basically a promise to such a compiler to not take the address of a local in the function body (this is the only standard way in which it affects C semantics!). But we haven't had such compilers for a very long time now, even when targeting embedded - the compilers themselves run on full-power hardware, so there's no reason for them to take shortcuts.
I realize that's a gnu extension - but it's super useful!
So if you want to make absolutely sure that a variable can always be in a register then you should consider adding the register specifier to stop other programmers from taking the address of that variable.
OTOH I didn't recall this bit, but apparently you can also apply it to arrays. Which keeps them indexable, but you can't take addresses of elements nor of the whole array anymore. Now I'm not sure if the compiler can do anything useful with this, but it would allow it to play with alignment and padding - e.g. storing "register bool x[10]" as 10 words rather than 10 bytes. Is there any architecture on which that would be beneficial, though?