[Dylan16807]

But that's not "undefined behavior" either. The post misleads people.

Certain things are unspecified. It can call in any order for example.

Other things are undefined. If you do them your program is no longer valid at all, and can crash or corrupt.

[nitrogen]

To reiterate/emphasize this point: "undefined", "unspecified", and a few other related terms are Things in C. They have specific, non-interchangeable, well-defined meanings in the C specifications.