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Postings from October 2003
Gisle Aas <gisle@ActiveState.com> writes:
> The following invariant should always hold if SvPOK(sv):
>
> - SvCUR(sv) < SvLEN(sv)
> - *SvEND(sv) == '\0'
>
> The perl core ensures that and so should extensions. The perlguts
> manpage says:
>
> All SVs that contain strings should be terminated with a
> NUL character. If it is not NUL-terminated there is a
> risk of core dumps and corruptions from code which passes
> the string to C functions or system calls which expect a
> NUL-terminated string.
I just wanted to follow up on this with one more point. It's not only
for external APIs this is important. You will also find code that
does things like this:
char *s = SvPVX(sv);
//...
while (isDIGIT(*s))
s++;
This is unsafe unless the invariant described above holds. The perl
core is full of similar cases and I know I've depended on this a lot
in the HTML::Parser module and other places.
--Gisle
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