[This is both a C and C++ bug report, not sure how to classify that.]
int a[256];
int A(char c) { return a[c]; } // C and C++ warnings, OK.
int D(void) { return a['%']; } // Spurious C++ warning, no C warning
int B(void) { return a['å']; } // C++ warning, missing C warning
int C(void) { return a['\300']; } // C++ warning, missing C warning
So,
g++ -Wchar-subscripts warns "array subscript has type 'char'" about
arr['%'] even though the index is guaranteed positive. gcc does not.
OTOH, gcc does not warn about a['\300'] or a['å'] (8-bit a-ring), even
with -fsigned-char which ensures that the subscript is negative.
Note, arr['@'] COULD be a bug in the program with characters like @ which
are not in the basic execution character set: C99 5.2.1p3; I haven't got
the C++ standard. Only characters in that character set are guaranteed
to be positive: C99 6.2.5p3. If the program is intended to be portable
to other character sets, it is buggy. Even if gcc doesn't support a
machine with that charset - if anyone does these days:-) So it might
make sense to have a -Wchar-subscripts=2 warning which only assumes the
basic execution character set, not the current character set.
In preprocessor expressions I don't know if it should check the source
or execution character set, or both...
--
Summary: Issues with -Wchar-subscripts
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: h dot b dot furuseth at usit dot uio dot no
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29455
