Re: How does string.format handle undefined behavior?

[nobody <nobody+lua-list@...>]

On 27/08/2021 16.28, Roberto Ierusalimschy wrote:
> Thanks for the report. Do you have any real case where this is causing
> problems? (e.g., a platform with a weird behavior for these uses, a tool
> that complains about Lua source code.)

For reference, the standard *explicitly* says "behavior is undefined"
and not just unspecified, but I tried both gcc and clang in gnu99 and
C11 modes with -fsanitize=undefined and neither of them produced any
warnings when formatting "%02c" or "%#02.4c" and other nonsense.  (That
said, as far as I understand UBSAN isn't supposed to catch _everything_,
just a subset of all undefined stuff.)

> > And from testing them on my machine, 
> > string.format("%02c",string.byte"1") results in "01", so it isn't 
> > ignored.

On my machine, "%02c" produces " 1" so while it seems to be not truly
undefined "in practice", at least the behavior can't be relied on.

Cheers!
-- nobody