Unexpected failure-to-warn

[Thomas Womack]

#include <iostream>
using std::cout;

int main(void)
{
   const int w = w/3;
}

does not give a 'warning, w may be used uninitialised', even when compiled 
with g++ -Wall, even though that's clearly the case.  I ran into this in 
real code - it's a common kind of thinko.

Is this a bug, or am I missing something subtle in the C standard?

Thomas Womack, Global Phasing Ltd.