Does “Undefined Behavior” really permit *anything* to happen? [duplicate]

Answer 1

Undefined behavior is simply the result of a situation coming up that the writers of the specification did not foresee.

Take the idea of a traffic light. Red means stop, yellow means prepare for red, and green means go. In this example people driving cars are the implementation of the spec.

What happens if both green and red are on? Do you stop, then go? Do you wait until red turns off and it's just green? This is a case that the spec did not describe, and as a result, anything the drivers do is undefined behavior. Some people will do one thing, some another. Since there is no guarantee about what will happen you want to avoid this situation. The same applies to code.