Is strlen on a string with uninitialized values undefined behavior?

Question

strlen returns the number of characters that precede the terminating null character. An implementation of strlen might look like this:

Answer 1

Yes, it's undefined behaviour. From the draft C11 standard, §J.2 "Undefined behavior":

The behavior is undefined in the following circumstances:

...

The value of an object with automatic storage duration is used while it is indeterminate.