GotW #97: Assertions (Difficulty: 4/10)

Assertions have been a foundational tool for writing understandable computer code since we could write computer code… far older than C’s assert() macro, they go back to at least John von Neumann and Herman Goldstine (1947) and Alan Turing (1949). [1,2] How well do we understand them… exactly?

[Updated Jan 2: On second thought, I’ll break the “assertions” and “postconditions” into two GotWs. This GotW has the assertion questions, slightly reordered for flow, and #98 will cover postconditions.]

JG Questions

1. What is an assertion, and what is it used for?

2. C++20 supports two main assertion facilities:

assertstatic_assert

For each one, briefly summarize how it works, when it is evaluated, and whether it is possible for the programmer to specify a message to be displayed if the assertion fails.

Guru Questions

3. If an assertion fails, what does that indicate, and who is responsible for fixing the failure? Refer to the following example assertion code in your answer.

void f() {
int min = /* some computation */;
int max = /* some other computation */;

// still yawn more yawn computation

assert (min <= max); // A

// ...
}

4. Are assertions primarily about checking at compile time, at test time, or at run time? Explain.

Notes

Thanks to Wikipedia for pointing out these references.

[1] H. H. Goldstine and J. von Neumann. “Planning and Coding of problems for an Electronic Computing Instrument” (Report on the Mathematical and Logical Aspects of an Electronic Computing Instrument, Part II, Volume I, p. 12; Institute for Advanced Study, April 1947.)

[2] Alan Turing. “Checking a Large Routine” (Report of a Conference on High Speed Automatic Calculating Machines, pp. 67-9, June 1949).