CPlusPlus Interview Questions and Answers

Answer - 91 : - 1.   "mutable" is a C++ keyword. When we declare const, none of its data members can change. When we want one of its members to change, we declare it as mutable. 2.   A "mutable" keyword is useful when we want to force a "logical const" data member to have its value modified. A logical const can happen when we declare a data member as non-const, but we have a const member function attempting to modify that data member. For example: class Dummy { public: bool isValid() const; private: mutable int size_ = 0; mutable bool validStatus_ = FALSE; // logical const issue resolved }; bool Dummy::isValid() const // data members become bitwise const { if (size > 10) { validStatus_ = TRUE; // fine to assign size = 0; // fine to assign } }

Answer - 92 : - Could you write a small program that will compile in C but not in C++ ? In C, if you can a const variable e.g. const int i = 2; you can use this variable in other module as follows extern const int i; C compiler will not complain. But for C++ compiler u must write extern const int i = 2; else error would be generated. Bitwise Operations - Given inputs X, Y, Z and operations | and & (meaning bitwise OR and AND, respectively), what is output equal to in? output = (X & Y) | (X & Z) | (Y & Z);   C++ Object-Oriented Interview Questions And Answers

Answer - 93 : - A modifier, also called a modifying function is a member function that changes the value of  at least one data member. In other words, an operation that modifies the state of an object. Modifiers are also known as ‘mutators’. Example: The function mod is a modifier in the following code snippet: class test { int x,y; public: test() { x=0; y=0; } void mod() { x=10; y=15; } };

Answer - 94 : - An accessor is a class operation that does not modify the state of an object. The accessor functions need to be declared as const operations

Answer - 95 : - A name clash occurs when a name is defined in more than one place. For example., two different class libraries could give two different classes the same name. If you try to use many class libraries at the same time, there is a fair chance that you will be unable to compile or link the program because of name clashes.

Answer - 96 : - It is a feature in C++ to minimize name collisions in the global name space. This namespace keyword assigns a distinct name to a library that allows other libraries to use the same identifier names without creating any name collisions. Furthermore, the compiler uses the namespace signature for differentiating the definitions.

Answer - 97 : - A using declaration makes it possible to use a name from a namespace without the scope operator.

Answer - 98 : - A class that is used to traverse through the objects maintained by a container class. There are five categories of iterators: input iterators, output iterators, forward iterators, bidirectional iterators, random access. An iterator is an entity that gives access to the contents of a container object without violating encapsulation constraints. Access to the contents is granted on a one-at-a-time basis in order. The order can be storage order (as in lists and queues) or some arbitrary order (as in array indices) or according to some ordering relation (as in an ordered binary tree). The iterator is a construct, which provides an interface that, when called, yields either the next element in the container, or some value denoting the fact that there are no more elements to examine. Iterators hide the details of access to and update of the elements of a container class. The simplest and safest iterators are those that permit read-only access to the contents of a container class.

Answer - 99 : - Incomplete types refers to pointers in which there is non availability of the implementation of the referenced location or it points to some location whose value is not available for modification. int *i=0x400 // i points to address 400 *i=0; //set the value of memory location pointed by i. Incomplete types are otherwise called uninitialized pointers.

Answer - 100 : - A dangling pointer arises when you use the address of an object after its lifetime is over. This may occur in situations like returning addresses of the automatic variables from a function or using the address of the memory block after it is freed. The following code snippet shows this: class Sample { public: int *ptr; Sample(int i) { ptr = new int(i); } ~Sample() { delete ptr; } void PrintVal() { cout << "The value is " << *ptr; } }; void SomeFunc(Sample x) { cout << "Say i am in someFunc " << endl; } int main() { Sample s1 = 10; SomeFunc(s1); s1.PrintVal(); } In the above example when PrintVal() function is called it is called by the pointer that has been freed by the destructor in SomeFunc.