[Bug other/94182] New: Document -Wchar-subscripts

[Bug other/94182] New: Document -Wchar-subscripts

[roland.illig at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94182

            Bug ID: 94182
           Summary: Document -Wchar-subscripts
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roland.illig at gmx dot de
  Target Milestone: ---

The current documentation on the -Wchar-subscripts option is nearly useless
since it doesn't explain anything. I've made an attempt to summarize and
explain the situation here:

https://stackoverflow.com/a/60696378

The GCC documentation should at least include some pointers where to find more
information about this warning, especially since there are so many ways to fix
the warning incorrectly.

[Bug other/94182] Document -Wchar-subscripts

[roland.illig at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94182

--- Comment #1 from Roland Illig <roland.illig at gmx dot de> ---
https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

[Bug other/94182] Document -Wchar-subscripts

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94182

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Considering it is documented in another place where char is signed or unsigned.
 I don't know if this needs to change.


https://gcc.gnu.org/onlinedocs/gcc-9.3.0/gcc/Characters-implementation.html#Characters-implementation

Which of signed char or unsigned char has the same range, representation, and
behavior as “plain” char (C90 6.1.2.5, C90 6.2.1.1, C99 and C11 6.2.5, C99 and
C11 6.3.1.1).
Determined by ABI. The options -funsigned-char and -fsigned-char change the
default. See Options Controlling C Dialect.


----- CUT -----
Plus -funsigned-char/-fsigned-char

[Bug other/94182] Document -Wchar-subscripts

[roland.illig at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94182

--- Comment #3 from Roland Illig <roland.illig at gmx dot de> ---
(In reply to Andrew Pinski from comment #2)
> Considering it is documented in another place where char is signed or
> unsigned.  I don't know if this needs to change.

Given only the compiler warning about "char subscript", how could I possibly
get to the documentation you linked?

> int demo(char ch, int *data) {
>     return data[ch];
> }

When I try to compile this code, I get:

> bad.c:2:16: warning: array subscript has type 'char' [-Wchar-subscripts]

>From there I can look up the documentation of that command line option. But how
could I get from there to your documentation? And, considering an _average_ GCC
user (instead of an active GCC developer), would I have a chance of
understanding the underlying problem and fixing it correctly? The GCC
documentation should at least try to educate the reader a bit.

[Bug other/94182] Improve -Wchar-subscripts documentation

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94182

Eric Gallager <egallager at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
                 CC|                            |egallager at gcc dot gnu.org
            Summary|Document -Wchar-subscripts  |Improve -Wchar-subscripts
                   |                            |documentation
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-05-19
             Status|UNCONFIRMED                 |NEW

--- Comment #4 from Eric Gallager <egallager at gcc dot gnu.org> ---
retitling to clarify what exactly the issue is, and confirming