https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66028
Bug ID: 66028
Summary: false positive, unused loop variable
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ncm at cantrip dot org
Target Milestone: ---
struct range {
int start; int stop;
struct iter {
int i;
bool operator!=(iter other) { return other.i != i; };
iter& operator++() { ++i; return *this; };
int operator*() { return i; }
};
iter begin() { return iter{start}; }
iter end() { return iter{stop}; }
};
int main()
{
int power = 1;
for (int i : range{0,10})
power *= 10;
}
bug.cc: In function ‘int main()’:
bug.cc:15:13: warning: unused variable ‘i’ [-Wunused-variable]
for (int i : range{0,10})
Manifestly, i is used to count loop iterations. The warning cannot be
suppressed by any decoration of the declaration; the best we can do is
void(i), power *= 10;
in the loop body. The warning is useful in most cases. The exception might be
that, here, the iterator has no reference or pointer members, and the loop body
changes external state.
[This matches clang bug https://llvm.org/bugs/show_bug.cgi?id=23416)
