>1 undefined behavior

>behavior, upon use of a non portable or erroneous program construct or of erroneous data, for which this International Standard imposes no requirements

>2 NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message), to terminating a translation or execution (with the issuance of a diagnostic message).

>3 EXAMPLE An example of undefined behavior is the behavior on integer overflow.

Yeah, that is obvious, but is there a example, where a defined variable is not clear defined and ambigious?