Exercise 19 of The Pragmatic Programmer

Question

This is taken from Exercise 19 of The Pragmatic Programmer.

A quick reality check. Which of these "impossible" things can happen?:

1. A month with fewer than 28 days

2. stat("." ,&sb) == -1 (that is, can't access the current directory)

3. In C++: a = 2; b = 3; if (a + b != 5) exit(1);

4. A triangle with an interior angle sum ≠ 180 °

5. A minute that doesn't have 60 seconds

6. In Java: (a + 1) <= a

I have some answers but I don't think my answers are "right" (in the sense that it is the answer that the writers were thinking about when they wrote the question).

This is my attempt:

1) September 1752

2) --I think we can skip this, not understanding the question--

3) I don't know C++, but is it something to do with threading and volatile variables (like Java) ?

4) impossible..

5) Due to occurence of leap Seconds

6) double a = 100000000000000001d;

I was wondering does anyone know the correct answer to these questions?

Answer 1

3: If a and b are of class type then the overloaded operator+ could do anything (or an overloaded assignment operator, or operator !=, or even an implicit conversion operator for that matter).

4: A triangle on a curved surface does not have an interior angle sum of 180.

6: Overflow in a.

The point of the questions is IMHO to demonstrate that a lot of "impossible" things do actually happen, and that you might not just be being paranoid when you are programming very defensively.

Answer 2

2 can happen quite easily. e.g. If you delete your directory while you're in in it and then execute something. Many programs actually handle this.

noufal@sanitarium% ls
noufal@sanitarium% cd
noufal@sanitarium% mkdir /tmp/foo
noufal@sanitarium% cd /tmp/foo
noufal@sanitarium% touch x
noufal@sanitarium% ls
x
noufal@sanitarium% rm -Rf /tmp/foo
noufal@sanitarium% ls
noufal@sanitarium% touch x
touch: cannot touch `x': No such file or directory

Answer 3

nr 5 happens in the case of leap seconds