Undefined behavior in c/c++: i++ + ++i vs ++i + i++ [duplicate]

Answer 1

int j = ++i + i++;

is still undefined behavior since ++i and i++ can be processed simultaneously in multiple pipelines in some CPUs, which will lead to unpredictable results.

Answer 2

int i = 1;
int j = i++ + ++i;

Evaluation will happen from Right to left, i.e. firstly ++i will be processed then i++. So j will have value 4.

You will get a warning that "operation on 'i' may be undefined" but there is no problem with this expression.

Answer 3

No, you are not correct. Each of the expressions ++i and i++ modify i, so the statement modifies i more than once. That is undefined behaviour.

Note that more recent versions of the standards no longer include the concept of "sequence point".