Is reading an indeterminate value undefined behavior?

Question

The question arose in the comments of an answer to the question Is C/C++ bool type always guaranteed to be 0 or 1 when typecast\'ed to int?

The code in question allo

Answer 1

yes, formally an rvalue conversion of indeterminate value is UB (except for unsigned char, originally i wrote "and variants" but as i recall the formal caters to 1's complement signed char where possibly minus 0 could be used as trap value)

i'm too lazy to do the standard paragraph lookup for you, and also to lazy to care about downvotes for that

however, in practice only a problem on (1) archaic architectures, and perhaps (2) 64-bit systems.

EDIT: oops, i now seem to recall a blog posting and associated Defect Report about formal UB for accessing indeterminate char. so perhaps i'll have to actually check the standard, + search DRs. argh, it will have to be later then, now coffee!

EDIT2: Johannes Schaub was kind enough to provide this link to SO question where that UB for accessing char was discussed. So, that's where I remembered it from! Thanks, Johannes.

cheers & hth.,