Re: string::iterator should have more error checking

[Frederick Virchanza Gotham <cauldwell.thomas@gmail.com>]

On Fri, Jun 24, 2022 at 10:35 AM Jonathan Wakely <jwakely@redhat.com> wrote:

> That's expected. The contents of the string_view are a string literal,
> which is in the program image, not on the heap.


Valgrind is the best tool for troubleshooting heap problems (although
it's useless against non-heap problems).


> AddressSanitizer
> doesn't check access to such memory.
> The byte after the string literal "brush" is uninitialized, but it
> does exist in a valid memory page.


Check out how "-fsanitize" flags the following invalid access to
static-duration constexpr arrays:

        https://godbolt.org/z/fjnPTWj5P

Having thought about this a little more, I realise that "brush" in memory is:

      char constexpr brush[6u] = { 'b', 'r', 'u', 's', 'h', '\0' };

And so therefore it is perfectly valid to access the null terminator
located at brush[5u], which is why the access is not flagged by
"-fsanitize".


> And it's not detected by Debug Mode because string_view iterators are
> just pointers.


I understand that. I think there should be "<debug/string_view>" and
that it should be optionally configurable to barf when it encounters a
null terminator. (It must be optionally configurable because a null
char is actually a valid char inside a string_view). Something like:

    #define _GLIBCXX_STRINGVIEW_DONT_ALLOW_NULL_CHAR
    #include <debug/string_view>