Christoph Groth <cwg@xxxxxxxx> writes:
> when I compile the attached program with
>
> g++ -Wall -Wextra -O2 test.cc
>
> I get the following output:
>
> test.cc: In function ‘int main()’:
> test.cc:198: warning: ‘point.Tiny_vector<double, 1>::x[0u]’ may be used uninitialized in this function
> test.cc:198: note: ‘point.Tiny_vector<double, 1>::x[0u]’ was declared here
>
> That's with gcc 4.4.4.
>
> Is this warning unjustified or am I missing some subtlety? It's weird that the
> warning is only given for foo<1>.
> template <int D>
> Tiny_vector<double, D> foo()
> {
> Tiny_vector<double, D> point;
> do {
> for (int i = 0; i < D; ++i) point[i] = double(rand()) / RAND_MAX;
> } while(dot(point, point) > 1);
> return point;
> }
As far as I can see the warning is unjustified. The compiler was smart
enough to see that i == 0 is always true within the loop, and used that
to promote the only array element into a local variables. However it
wasn't smart enough to unwind the nested control structure to see that
the value is always set before it is used. In effect the compiler sees
that the inner loop could exit, and doesn't see that by the time it
exits point[0] must always be set. The warning doesn't happen for
foo<2> because in that case the compiler does not promote the
If you can, please file a bug report about this, following the
directions at http://gcc.gnu.org/bugs/ . Thanks.
Ian
