thiago I used NULL there to indicate what would be passed if something like
the following occurred:

int leng = 0, index = 0;
char *text = foo(&leng,&index);
// oops didn't check foo succeeded:
snprintf( buff, max, ".*s", leng, text + index );

On Thu, 31 Jul 2025 at 16:59, Thiago Macieira via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> On Thursday, 31 July 2025 08:56:26 Pacific Daylight Time zxuiji via Std-
> Proposals wrote:
> > snprintf( buff, max, "%.*s", length, NULL + index. ) could catch the
> > invalid pointer (so long as index is small) before a segfault can occur
> and
> > if stdlib is not in debug mode then allow the segafault to occur,
> otherwise
> > return -1 and set errno to some relevant value
>
> Do note that the program is UB before snprintf() was called.
>
> Could such a check function ever be used *before* UB happened?
>
> --
> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
> Principal Engineer - Intel Platform & System Engineering
>
>
>
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