Thread: bit shifting...undefined behaviour?

Originally Posted by Sebastiani

sorry, that was a typo. anyway, to put it more clearly, shouldn't a shift always produce cleared bits in the vacated positions (unless the number of shifts exceeds the size of the data type, which is undefined)?

For a left shift, yes. For a right shift, it depends on whether the integral type is signed or unsigned. For an unsigned type, yes again. For a signed type, it does either an arithmetic shift or a logical shift, depending on the machine (logical shift is what you're thinking of).

http://en.wikipedia.org/wiki/Arithmetic_shift
http://en.wikipedia.org/wiki/Logical_shift

Edit: AFAIK, nothing undefined happens if the number of shifts exceeds the size of the data type, it does what you would expect.