GotW #102: Assertions and “UB” (Difficulty: 7/10)

This special Guru of the Week series focuses on contracts. Now that we have considered assertions, postconditions, and preconditions in GotWs #97-101, let’s pause and reflect: To what extent does a failed contract imply “UB”… either the Hidden Dragon of Undefined Behavior, or the Crouching Tiger of Unspecified Behavior?

JG Question

1. Briefly, what is the difference among:

(a) undefined behavior

(b) unspecified behavior

(c) implementation-defined behavior

Guru Questions

2. For each of the following, write a short function of the form:

/*...function name and signature...*/{ assert( /*...some condition about the parameters...*/ ); /*...do something with parameters...*/;}

where if the assertion is not checked and is false then the effect:

(a) is always undefined behavior

(b) possibly results in undefined behavior

(c) is never undefined or unspecified behavior

3. Explain how your answers to Questions 1 and 2 do, or do not, correspond with each other.

4. BONUS: Describe a valuable service that a tool could perform for assertions that satisfy the requirement in 2(a), that is not possible for other assertions.