Advanced C++ and STL interview questions

Advanced C++ and STL interview questions

Q: How do you link a C++ program to C functions?

A: By using the extern "C" linkage specification around the C function declarations.

Q: Explain the scope resolution operator.

A: Scope resolution operator (::) permits a program to reference an identifier in the global scope that has been hidden by another identifier with the same name in the local scope.

Q: What are the differences between a C++ struct and C++ class?

A: Structures and classes are syntactically and functionally identical, except in the default accessibility of their members and their inheritance. By default, members of structures have public accessibility and public inheritance from their parent(s), while members of classes are private and inherit privately from their parent(s). Individual members' accessibility can be specified by using the public, protected and private keywords.

Q: How many ways are there to initialize an int with a constant?

A: Two.

There are two formats for initializers in C++ as shown in the example that follows. The first format uses the traditional C notation. The second format uses constructor notation.

int foo = 123;

int bar (123);

Q: How does throwing and catching exceptions differ from using setjmp and longjmp?

A: The throw operation calls the destructors for automatic objects instantiated since entry to the try block.

Q: What is your reaction to this line of code?

delete this;

A: It’s not a good practice.

Q: What is a default constructor?

A: A constructor that has no arguments, or all arguments have default values.

Q: What is a conversion constructor?

A: A constructor that accepts one argument of a different type.

Q: What is the difference between a copy constructor and an overloaded assignment operator?

A: A copy constructor constructs a new object by using the content of the argument object. An overloaded assignment operator assigns the contents of an existing object to another existing object of the same class.

Q: When should you use multiple inheritance?

A: There are three acceptable answers: "Never," "Rarely," and "When the problem domain cannot be accurately modeled any other way."

Q: What is a virtual destructor?

A: The simple answer is that a virtual destructor is one that is declared with the virtual attribute. When someone will delete a derived-class object via a base-class pointer.
In particular, here's when you need to make your destructor virtual:
* if someone will derive from your class,
* and if someone will say new Derived, where Derived is derived from your class,
* and if someone will say delete p, where the actual object's type is Derived but the pointer p's type is your class.
Confused? Here's a simplified rule of thumb that usually protects you and usually doesn't cost you anything: make your destructor virtual if your class has any virtual functions. Rationale:
* that usually protects you because most base classes have at least one virtual function.
* that usually doesn't cost you anything because there is no added per-object space-cost for the second or subsequent virtual in your class. In other words, you've already paid all the per-object space-cost that you'll ever pay once you add the first virtual function, so the virtual destructor doesn't add any additional per-object space cost. (Everything in this bullet is theoretically compiler-specific, but in practice it will be valid on almost all compilers.

Q: Explain the ISA and HASA class relationships. How would you implement each in a class design?

A: A specialized class "is" a specialization of another class and, therefore, has the ISA relationship with the other class. An Employee ISA Person. This relationship is best implemented with inheritance. Employee is derived from Person. A class may have an instance of another class. For example, an employee "has" a salary, therefore the Employee class has the HASA relationship with the Salary class. This relationship is best implemented by embedding an object of the Salary class in the Employee class.

Q: When is a template a better solution than a base class?

A: When you are designing a generic class to contain or otherwise manage objects of other types, when the format and behavior of those other types are unimportant to their containment or management, and particularly when those other types are unknown (thus, the genericity) to the designer of the container or manager class.

Q: What is a mutable member?

A: One that can be modified by the class even when the object of the class or the member function doing the modification is const. mutable keyword can only be applied to non-static and non-const data members of a class. If a data member is declared mutable, then it is legal to assign a value to this data member from a const member function.

Q: What is an explicit constructor?

A: A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. It’s purpose is reserved explicitly for construction.

http://weblogs.asp.net/kennykerr/archive/2004/08/31/Explicit-Constructors.aspx

The explicit keyword in C++ is used to declare explicit constructors. Explicit constructors are simply constructors that cannot take part in an implicit conversion. Consider the following example:

class Array
{
public:
Array(size_t count);
// etc.
};

This seems innocent enough until you realize that you can do this:

Array array = 123;

Well that’s ugly but hardly something to get excited about, or is it? This is known as an implicit conversion. The trouble is that it can occur in more insidious places. Consider the following function:

void UseArray(const Array& array);

Because the compiler will attempt to find an implicit conversion, the following code compiles just find:

UseArray(123);

Yikes! That’s terrible. First there is the problem of code clarity. What does this mean? Secondly, because the implicit conversion involves calling the Array constructor, presumably enough storage is being allocated for a new Array object, not to mention the memory reserved for 123 elements contained in the array. Surely this is not what the programmer intended!?

All of these subtleties can be avoided by making the Array constructor explicit:

class Array
{
public:
explicit Array(size_t size);
// etc.
};

Now a programmer needs to be explicit about her use of the Array constructor.

Array array(123);
UseArray(Array(123));

A thing of beauty.

Q: What is the Standard Template Library?

A: A library of container templates approved by the ANSI committee for inclusion in the standard C++ specification.

A programmer who then launches into a discussion of the generic programming model, iterators, allocators, algorithms, and such, has a higher than average understanding of the new technology that STL brings to C++ programming.

Q: Describe run-time type identification.

A: The ability to determine at run time the type of an object by using the typeid operator or the dynamic_cast operator. The typeid operator provides a program with the ability to retrieve the actual derived type of the object referred to by a pointer or a reference. This operator, along with the dynamic_cast operator, are provided for run-time type identification (RTTI) support in C++.

Q: What problem does the namespace feature solve?

A: Multiple providers of libraries might use common global identifiers causing a name collision when an application tries to link with two or more such libraries. The namespace feature surrounds a library’s external declarations with a unique namespace that eliminates the potential for those collisions.

This solution assumes that two library vendors don’t use the same namespace identifier, of course.

Q: Are there any new intrinsic (built-in) data types?

A: Yes. The ANSI committee added the bool intrinsic type and its true and false value keywords.Q: How does throwing and catching exceptions differ from using setjmp and longjmp?