Re: C++ interview questions

James Kanze <>
Tue, 4 Mar 2008 02:20:00 -0800 (PST)
On Mar 3, 7:34 pm, "Victor Bazarov" <> wrote:

arn...@arch.i-did-not-set--mail-host-address--so-tickle-me wrote:

After1 month from now, I will start giving job interviews.
Searchign at Google led me to several common questions asked
in interviewers looking for C++ based programmers. I have
titled it "C++ interview questions - 1 (technical)" as,
after sometime, I will start another thread titled "C++
interview questions (general)":

I searched for the archives too but didn ot get answers:

 1.) Why array index start at 0 (zero) ?

I got these results but I can't know which one is right:




I didn't look at the given answers, but my guess would be
"because in C it was, and it made sense, so Stroustrup kept
it". The person interviewing you may not go along with the
humour, so you could try "because indexing is done using the
'base address + offset' method, and the easiest way to
calculate the offset is to multiply the index (which has to
start with 0) by the size of the object.

My reaction would be that in C++, they don't have to be:-).
Although they are for the components of the standard library, my
pre-standard array classes followed the Pascal approach: you
specify the upper and lower bounds. Although unlike Pascal, I
used a half open interval, with the upper bounds exclusive.

A more interesting question would be why the lower bound should
be 0 in most cases, even when you have a choice.


  3.) How is static variable stored in the memory ?

However the compiler likes?

That's a good example of the sort of question that makes no

I got these and they say "It is not defined in the C++ & C Standard":


This reminds me of a question I once got in an interview: what
does the keyword static mean in C++. The answer they were
looking for was "not on the stack". That answer never occured
to me, and because of that, I didn't get the job. (I'm willing
to bet, however, that I was more competent than whoever finally
did get it.)

  4.) what is an escaping variable?


I think in both questions (3rd and 4th ) "Victor Bazarov" is
right but what should I answer in front of an HR ?

Tell him "Victor Bazarov" told you to answer it so :-)

I'll admit that I'd draw a blank on this one. I've never heard
of the term.

I don't guess I'd get this job either, if I were a candidate.

 5.) How can you force instantiation of a Template ?

Use an explicit template instantiation. Syntax is similar to
a template declaration (it also begins with the keyword
"template" ) but without the following angle brackets.

Or just use the template, period. If you call a template
function, it's going to be instantiated. If you definie a
variable with a class template type, the template is going to be

The question sounds a bit too vague to me.

 6.) What is a Framework in C++ ?

A Framework is not really a C++ term.

Which isn't a reason not to ask it. In my experience, questions
about design and patterns are generally more important than
those which directly concern C++.


 7.) What happens to the member functions in the class when copy
 constructor is invoked ?


Yes, what happens to them? Another question to which I don't
know the answer.

 8.) What are the different types of storage classes ?

"Storage classes"? Do you mean standard containers?

In the standard, storage class specifiers has a very precise
definition: one of register, static, extern or mutable. If
being perfectly fluent in standardese is an important
qualification for the job, then this is a good question, and you
just failed. The exact answer is rather irrelevant for most C++
programming jobs, however.

If I really wanted to ask something along these lines, it would
be more like "what are the different storage durations supported
by C++, and give an example of an object which has each." Or
even: "what is the difference between storage duration and
object lifetime" (although that to is edging very near just
being an explination of standardese).

 9.) What is the difference between function-overloading and
 operator-overloading ?

a. Operators have particular meaning.
b. One's not allowed to overload operators for built-in types.

The name of the functions have a different syntax, and
overloaded operators can also be called with a different syntax.
For extra credit: with overloaded operators, the overload set
can include both member and non-member functions; for an
overloaded function, it will always be one or the other.

 10.) Is there any way to write a class so that no class can be
 iinherited from it ?

Yes. See Stroustrup's home page, and his C++ technical FAQ list.

Nice piece of trivia, but not interesting for an interview


 12.) How to create an object so that it should not call its
 constructor by default ?

Who should not call its what?

I don't understand the question. Another one we got wrong. (I
don't think either of us is going to get the job:-).)


 14.) what is the difference between static global variable
 and static local variable ?

The difference is in the time they are initialised, and their

(I always thought that there is nothing like "static global

Any variable declared/defined at the namespace scope is
_glogal_. And it has static storage duration, which makes it

The word "static" in C++ has a lot of different meanings. If
he's refering to the keyword, declaring a global variable
"static" means that it has internal linkage, rather than
external. Declaring a local variable "static" means that it has
static lifetime, rather than automatic. All global variables
have static lifetime (even if they're not "static"), and local
variables never have linkage.

And now that everybody's completely confused... :-) (And I
forgot: "static" means that it's not on the stack, regardless of
where it appears. Even on a function.)

Seriously, I'd never ask a question about static without
specifying what I meant by it: the keyword, or lifetime.

 15.) What are the types of STL containers ?

There are two: sequencial and associative.

There are three: sequential, associative and unordered
associative. At least in C++0x (which, given the current date,
should be relevant real soon now).

(I think that they are typeless)


Hmmm. It's true that the word "type" also has a very specific
meaning in the standard (and all of the STL containers are
templates, i.e. have a generic type). But I'd say that the
wording of the question makes it clear that the more general
meaning is meant here (which means that your answer was

 16.) What are Polymorphic Classes ?

(Classes which are related by polymorphism. It means, they have
similar operations and are derived from some other classes which , in
fact, have inherited the same base class)

That's incorrect. Polymorphic class is one that can be used
polymorphically. In C++ it means it derives from a base class
that has virtual functions.

Again: does he mean in standardese, or in everyday use. In the
standard a polymorphic class is one that has one or more virtual
functions. Regardless of how you use it. In more general use
(OO design, etc.), one might not consider private bases as an
example of polymorphism.

In this regard, I'd probably ask about the LSP. If I wanted
something more C++ specific: why and when would you declare a
destructor virtual?

 19.) What is a memory leak ? How we can avoid it ?

A memory leak is the result of allocating memory and losing
any information about it which would allow freeing it later.
To avoid memory leaks, deallocate all memory you have

I don't agree. A memory leak is the result of not freeing
dynamic memory that you don't need any more. Just having the
information about it isn't any good if you don't use it. Even
if the application is using garbage collection, for example, you
must ensure that you don't keep pointers which you don't use.

 20.) what is the difference between wait() and delay() ?

Those are not C++ terms.

And I've never heard of delay().

 21.) What is the difference a fake pointer and a smart pointer ?

(ouch!, I did not even know that there is a thing called
"fake pointer" )

I don't know what a "fake pointer" is.

Me neither.

Here are some funny interviews questions:

What's so funny about those?

- What is the difference a Function and a Member-Function ?

That is not a complete sentence in English. The difference
_between_ a function and a member function exists and it's not

- What is the virtual class and friend class ?

No such thing as "virtual class", but there is a "virtual base
class" -- read up on those.

There's also an abstract class, and in most cases, asking
something about them might be a good idea. (E.g. what is an
abstract class, and when would you use one?)

Friend class -- open your C++ book and read.

- What is the difference C and C++ ?

That is not a complete sentence in English. The difference
*between* C and C++ is vast - C++ has many more rules and
constructs for object- oriented and generic progamming.

They're two different languages?

- What is namespace ?

It is a combination of all names (types, functions, and
objects) declared in it. Namespaces participate in a certain
way in name resolution. Namespace is a mechanism to both
bring some names close together (by containing them in one
name resolution region) and separate them (by containing them
in different name resolution regions). Namespaces help
establishing logical boundaries between sets of names used in
the program.

Again: is he referring to the keyword, or the general concept.
When I learned C, I learned that struct tags were in a
different namespace than other symbols. Which certainly has
nothing to do with the C++ keyword namespace. Note that even
when talking about C++, it's frequent to say things like "names
beginning with a double underscore are in the implementation

Anyway, if this is an example of the questions they ask in the
interview, I don't think I'd get the job. And yet, I'd
consider myself a pretty competent C++ programmer.

James Kanze (GABI Software)
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