On Tue, Mar 3, 2026 at 2:53 PM Evgeny Kotkov via dev < [email protected]> wrote:
> Branko Čibej <[email protected]> writes: > > > There is something fishy going on here. For example, this is the > prototype > > for strstr: > > > > char *strstr(const char*, const char*); > > The relevant change here could be the C23 proposal "N3020 - Qualifier- > preserving Standard Functions", which updated these functions to preserve > const qualifiers [1, 2]: > > QChar *strstr (QChar *s1, const char *s2); > > [where QChar stands for "qualified char"] > > The prototype `char *strstr (const char*, …)` seems to have been a > workaround > for the lack of function overloading in C. But the downside is that it > does > not preserve constness and effectively works like an implicit const_cast. > I did not know how that works. Thanks for explaining! > > > + char *p = NULL; > > char *ep = NULL; > > int sd; > > > > This makes no sense. Not only is 'p' already const, nothing is being > > modified through '*p' but something _is_ being modified through '*ep'. > > I think the underlying question here and in similar cases is how the > non-const > `char* ep` was obtained from `const char *p` in the first place. > > In trunk, the const qualifier seems to be silently stripped away when > passing > the pointer to functions like strstr() or strchr(): > > ep = strchr(p, '\n'); > > Type-wise, this is equivalent to: > > ep = (char*)p; > > and it's problematic, because it discards the const from the original > pointer. > > To some extent, I would say that using `const char *` is even misleading if > it's the only pointer available, as it obscures the fact that the data > eventually get modified without any explicit typecasts: > > const char *keyword = APR_ARRAY_IDX(keyword_tokens, i, const char *); > /* The only pointer we had originally was const. */ > > if (expand_custom_keywords) > { > char *sep; > > sep = strchr(keyword, '='); > if (sep) > { > *sep = '\0'; /* But then the data is modified here > without typecasts */ > > [1]: > https://thephd.dev/c23-is-coming-here-is-what-is-on-the-menu#n3020---qualifier-preserving-standard-functions > [2]: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3020.pdf > > > Thanks, > Evgeny Kotkov > -- Timofei Zhakov
