"x = ++x" is it really undefined?

user_429618 0
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I am using Coverity Prevent on a project to find errors.

It reports an error for this expression (The variable names are of course changed):

x=
   (a>= b) ?
   ++x: 0;

The message is:

EVALUATION_ORDER defect: In "x=(a>= b) ? ++x: 0;", "x" is written in "x" (the assignment LHS) and written in "(a>= b) ? ++x: 0;" but the order in which the side effects take place is undefined because there is no intervening sequence point. END OF MESSAGE

While I can understand that "x = x++" is undefined, this one is a bit harder for me. Is this one a false positive or not?

coverity-prevent operator-precedence c++
6 Answers

In order to understand this you need to have a basic understanding of sequence points. See this link: http://en.wikipedia.org/wiki/Sequence_point

For the = operator there is no sequence point, so there is no guarantee that the value of x will be modified before it is again assigned to x.

user_12495190
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