The code:
#include <cstddef>
static const char lwb = 0x80;
static const char upb = 0x7f;
static const size_t cnt = upb - lwb + 1;
static const char lwba = 0x80;
static const char upba = 0x01;
static const size_t cnta = upba - lwba + 1;
static const char lwbb = 0xff;
static const char upbb = 0x7f;
static const size_t cntb = upbb - lwbb + 1;
static const char lwbc = 0x00;
static const char upbc = 0x7f;
static const size_t cntc = upbc - lwbc + 1;
int main() {
return 0;
}
gets you:
~/ootbc/common/src$ c++ foo.cc
foo.cc:5: warning: integer overflow in expression
foo.cc:9: warning: integer overflow in expression
foo.cc:13: warning: integer overflow in expression
which (as I read the promotion rules) is incorrect. First lwb and upb should be
promoted to int, then subtraction is done, and then the addition. This gives no
overflow. However, it appears that the subtraction is actually being done in
char, not int, because the results actually do overflow 127 on all but the last
case.
Have the promotion rules changed?
Ivan
--
Summary: incorrect overflow warning
Product: gcc
Version: 3.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: igodard at pacbell dot net
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20019
