C++ Interview questions Part 10

C++ interview question:When can you tell that a memory leak will occur?

Answer:A memory leak occurs when a program loses the ability to free a block of dynamically allocated memory. 

C++ interview question:What is a parameterized type?

Answer:A template is a parameterized construct or type containing generic code that can use or manipulate any type. It is called parameterized because an actual type is a parameter of the code body. Polymorphism may be achieved through parameterized types. This type of polymorphism is called parameteric polymorphism. Parameteric polymorphism is the mechanism by which the same code is used on different types passed as parameters. 

C++ interview question:Differentiate between a deep copy and a shallow copy? 

Answer:Deep copy involves using the contents of one object to create another instance of the same class. In a deep copy, the two objects may contain ht same information but the target object will have its own buffers and resources. the destruction of either object will not affect the remaining object. The overloaded assignment operator would create a deep copy of objects.

             Shallow copy involves copying the contents of one object into another instance of the same class thus creating a mirror image. Owing to straight copying of references and pointers, the two objects will share the same externally contained contents of the other object to be unpredictable.

Explanation:

                   Using a copy constructor we simply copy the data values member by member. This method of copying is called shallow copy. If the object is a simple class, comprised of built in types and no pointers this would be acceptable. This function would use the values and the objects and its behavior would not be altered with a shallow copy, only the addresses of pointers that are members are copied and not the value the address is pointing to. The data values of the object would then be inadvertently altered by the function. When the function goes out of scope, the copy of the object with all its data is popped off the stack. 

                    If the object has any pointers a deep copy needs to be executed. With the deep copy of an object, memory is allocated for the object in free store and the elements pointed to are copied. A deep copy is used for objects that are returned from a function. 

C++ interview question:What is an opaque pointer?

Answer:A pointer is said to be opaque if the definition of the type to which it points to is not included in the current translation unit. A translation unit is the result of merging an implementation file with all its headers and header files. 

C++ interview question:What is a smart pointer?

Answer:A smart pointer is an object that acts, looks and feels like a normal pointer but offers more functionality. In C++, smart pointers are implemented as template classes that encapsulate a pointer and override standard pointer operators. They have a number of advantages over regular pointers. They are guaranteed to be initialized as either null pointers or pointers to a heap object. Indirection through a null pointer is checked. No delete is ever necessary. Objects are automatically freed when the last pointer to them has gone away. One significant problem with these smart pointers is that unlike regular pointers, they don't respect inheritance. Smart pointers are unattractive for polymorphic code. Given below is an example for the implementation of smart pointers.

Example: 

template 

class smart_pointer

{

public:

smart_pointer(); // makes a null pointer

smart_pointer(const X& x) // makes pointer to copy of x

X& operator *( );

const X& operator*( ) const;

X* operator->() const;

smart_pointer(const smart_pointer &);

const smart_pointer & operator =(const smart_pointer&);

~smart_pointer():

private:

//...

};

This class implement a smart pointer to an object of type X. The object itself is located on the heap. Here is how to use it:

smart_pointer p= employee("Harris",1333);

Like other overloaded operators, p will behave like a regular pointer,

cout<<*p;

p->raise_salary(0.5);

C++ interview question:What is reflexive association?

Answer:The 'is-a' is called a reflexive association because the reflexive association permits classes to bear the is-a association not only with their super-classes but also with themselves. It differs from a 'specializes-from' as 'specializes-from' is usually used to describe the association between a super-class and a sub-class. For example:

Printer is-a printer.