Using an undefined value leads to undefined behavior under the C spec. This "undefined behavior" could be a visible side effect (in the helpful case, a diagnos

Using an undefined value leads to undefined behavior under the C spec. This "undefined behavior" could be a visible side effect (in the helpful case, a diagnostic on stderr like when you're using valgrind on your program; in the unhelpful case literal demons flying out of your nose) and it need not be the same on each use of the undefined value either.