I do not, contrary to the opinions of some (rather weepy) individuals, ask interview questions like, “name the types of C++ inheritance” then flog the interviewee for saying “virtual, non-virtual, single, multiple,” because I was expecting “public, private, protected.” Indeed, it’s been more than two years since I last had the opportunity to interview, but when I did, I made sure of two things:
What I Was Looking For
See, I am less interested in recommending someone for hire who has a bunch of facts memorized and more interested in hiring someone who took on self study learning. For instance, we were a Linux shop, so I would ask the person being interviewed about his or her favorite distro. If he didn’t have a favorite Linux distribution, or at least hold a conversation about the various ones out there, that told me that he had not really spent any time playing and learning on his own. That is a specific example that came up a few times, but isn’t necessarily fair in all cases.
Questions I Would Ask
I would probe the person being interviewed to see the depths of knowledge and skills. A favorite C++ question I asked in the last few interview I did was: “Give me a generic C++ function that will return the max of any two values of the same type given to it.” I got exactly 0 people who mentioned the obvious (and broken) C macro:
#define MAX(i,j) (i>j?i:j)
Not a single person mentioned the typesafe C++ way of doing it with a template. Actually, not a single person even mentioned the WORD template during an entire interview. Well, maybe one candidate did.
template<typename T>
const T& max(const T& left, const T& right) {
return left>right?left:right;
}
I would have ended the interview and recommended a hire on the spot for any candidate who said: “Well, you could just use std::max<>” Maybe it was just the people we were bringing in for interviews, but it was the level of question I needed to ask.
Cruel and Unusual Questions
I did have one guy interview who put “C++ Guru” on his resume. I went digging for some harder questions to ask him. He actually did well, but we didn’t hire him. I’m not sure I remember why now. These are the questions I wouldn’t ask, they are probably generally unfair, as knowing specific little details is not a good measure of the growth the developer might have. “What are the advantages and disadvantages of ADL (Argument Dependant Lookup)?” I would look for something like:
Advantages
Because of ADL code like: std::cout << "hello world" << std::endl can compile because the compiler can find operator<<(ostream &, const char*) in the namespace std automatically.
Disadvantages
ADL can cause unexpected results if the compiler finds a templated operator in a related namespace. (There are other criticisms on the wikipedia page I was not aware of.)
“What is the use of virtual inheritance and when would you want it?”
What Is It?
Virtual inheritance ensures that the same base class appearing two or more times in an inheritance graph has all of its instances merged.
When would you want it?
Probably anytime you have a diamond in your inheritance graph, but the details are up to the specific object model in question. It’s possible you actually want separate instances of each base class. Better answer: “You should probably simplify your object model to eliminate diamonds and rely more on generic/functional programming.”
“What does int i=0; printf("%i %i", ++i, i); print?”
Answer: The use of pre/post increment on the same statement as another use of the same variable is undefined, don’t do it.
“Describe for me the CRTP (Curiously Recurring Template Pattern) and give me an example of its usage.”
Answer: The CRTP is where a base class is given knowledge of a derived class via templates. Example:
//We can use the CRTP to allow the Base class to call a method of the derived class
//without incurring any virtual function call overhead
template<typename T>
class Base
{
public:
// Provide a <= operator to classes with < and ==
bool operator<=(const T& right) const
{
const T &left = static_cast<const T &>(this);
return left < right || left == right;
}
};
class Derived : public Base<Derived>
{
private:
int m_val;
public:
Derived(int t_val)
: m_val(t_val)
{
}
bool operator==(const Derived &t_right) const
{
return m_val == t_right.m_val;
}
bool operator<(const Derived &t_right) const
{
return m_val < t_right.m_val;
}
};
Maybe These are Reasonable Question Where You Work
If so, then by all means, but I had to verify a couple of the questions.