Technical interview questions and answers play a major role in C++ Interviews because C++ is widely used in system programming, game development, competitive coding, and performance-critical applications. Companies expect candidates to know OOP concepts, classes, inheritance, polymorphism, references, memory management, STL, and exception handling. These questions often appear in campus placements and software interviews conducted by TCS, Wipro, Infosys, Cognizant, and Capgemini. This guide covers frequently asked C++ interview questions with simple explanations that help freshers and job seekers strengthen their programming foundation. Preparing these questions will help you perform well in coding tests, technical rounds, and real-time problem-solving interviews.
1. What is a modifier?
Answer: 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.
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2. What is an accessor?
Answer: 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
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3. Differentiate between a template class and class template.
Answer: Template class:
A generic definition or a parameterized class not instantiated until the client provides the needed information. Its jargon for plain templates.
Class template:
A class template specifies how individual classes can be constructed much like the way a class specifies how individual objects can be constructed. Its jargon for plain classes.
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4. When does a name clash occur?
Answer: 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.
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5. Define namespace.
Answer: 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.
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6. What is the use of using declaration.
Answer: A using declaration makes it possible to use a name from a namespace without the
scope operator.
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7. List out some of the OODBMS available.
Answer: Ø GEMSTONE/OPAL of Gemstone systems.
Ø ONTOS of Ontos.
Ø Objectivity of Objectivity inc.
Ø Versant of Versant object technology.
Ø Object store of Object Design.
Ø ARDENT of ARDENT software.
Ø POET of POET software.
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8. List out some of the object-oriented methodologies.
Answer: Ø Object Oriented Development (OOD) (Booch 1991,1994).
Ø Object Oriented Analysis and Design (OOA/D) (Coad and Yourdon 1991).
Ø Object Modelling Techniques (OMT) (Rumbaugh 1991).
Ø Object Oriented Software Engineering (Objectory) (Jacobson 1992).
Ø Object Oriented Analysis (OOA) (Shlaer and Mellor 1992).
Ø The Fusion Method (Coleman 1991).
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9. What is an incomplete type?
Answer: 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.
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10. What is a dangling pointer?
Answer: 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.
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11. Differentiate between the message and method.
Answer: Message
Objects communicate by sending messages to each other.
A message is sent to invoke a method.
Method
Provides response to a message.
It is an implementation of an operation.
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12. What is an adaptor class or Wrapper class?
Answer: A class that has no functionality of its own. Its member functions hide the use of a
third party software component or an object with the non-compatible interface or a nonobject-
oriented implementation.
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13. What is a Null object?
Answer: It is an object of some class whose purpose is to indicate that a real object of that
class does not exist. One common use for a null object is a return value from a member
function that is supposed to return an object with some specified properties but cannot
find such an object.
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14. What is class invariant?
Answer: A class invariant is a condition that defines all valid states for an object. It is a
logical condition to ensure the correct working of a class. Class invariants must hold
when an object is created, and they must be preserved under all operations of the class. In
particular all class invariants are both preconditions and post-conditions for all operations
or member functions of the class.
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15. What do you mean by Stack unwinding?
Answer: It is a process during exception handling when the destructor is called for all local
objects between the place where the exception was thrown and where it is caught.
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16. Define precondition to a member function.
Answer: Precondition:
A precondition is a condition that must be true on entry to a member function. A
class is used correctly if preconditions are never false. An operation is not responsible for
doing anything sensible if its precondition fails to hold.
For example, the interface invariants of stack class say nothing about pushing yet
another element on a stack that is already full. We say that isful() is a precondition of the
push operation.
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17. Define post-condition to a member function.
Answer: Post-condition:
A post-condition is a condition that must be true on exit from a member function
if the precondition was valid on entry to that function. A class is implemented correctly if
post-conditions are never false.
For example, after pushing an element on the stack, we know that isempty() must
necessarily hold. This is a post-condition of the push operation.
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18. What are the conditions that have to be met for a condition to be an invariant of the
class?
Answer: Ø The condition should hold at the end of every constructor.
Ø The condition should hold at the end of every mutator(non-const) operation.
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19. What are proxy objects?
Answer: Objects that stand for other objects are called proxy objects or surrogates.
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20. Name some pure object oriented languages.
Answer: Ø Smalltalk,
Ø Java,
Ø Eiffel,
Ø Sather.
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22. What is a node class?
Answer: A node class is a class that,
Ø relies on the base class for services and implementation,
Ø provides a wider interface to te users than its base class,
Ø relies primarily on virtual functions in its public interface
Ø depends on all its direct and indirect base class
Ø can be understood only in the context of the base class
Ø can be used as base for further derivation
Ø can be used to create objects.
A node class is a class that has added new services or functionality beyond the services
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23. What is an orthogonal base class?
Answer: If two base classes have no overlapping methods or data they are said to be
independent of, or orthogonal to each other. Orthogonal in the sense means that two classes operate in different dimensions and do not interfere with each other in any way.The same derived class may inherit such classes with no difficulty.
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24. What is a container class? What are the types of container classes?
Answer: A container class is a class that is used to hold objects in memory or external
storage. A container class acts as a generic holder. A container class has a predefined
behavior and a well-known interface. A container class is a supporting class whose
purpose is to hide the topology used for maintaining the list of objects in memory. When
a container class contains a group of mixed objects, the container is called a
heterogeneous container; when the container is holding a group of objects th
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25. What is a protocol class?
Answer: An abstract class is a protocol class if:
Ø it neither contains nor inherits from classes that contain member data, non-virtual
functions, or private (or protected) members of any kind.
Ø it has a non-inline virtual destructor defined with an empty implementation,
Ø all member functions other than the destructor including inherited functions, are
declared pure virtual functions and left undefined.
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26. What is a mixin class?
Answer: A class that provides some but not all of the implementation for a virtual base
class is often called mixin. Derivation done just for the purpose of redefining the virtual
functions in the base classes is often called mixin inheritance. Mixin classes typically
don't share common bases.
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27. What is a concrete class?
Answer: A concrete class is used to define a useful object that can be instantiated as an
automatic variable on the program stack. The implementation of a concrete class is
defined. The concrete class is not intended to be a base class and no attempt to minimize
dependency on other classes in the implementation or behavior of the class.
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28. What is the handle class?
Answer: A handle is a class that maintains a pointer to an object that is programmatically
accessible through the public interface of the handle class.
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29. What is an action class?
Answer: The simplest and most obvious way to specify an action in C++ is to write a
function. However, if the action has to be delayed, has to be transmitted 'elsewhere'
before being performed, requires its own data, has to be combined with other actions, etc
then it often becomes attractive to provide the action in the form of a class that can
execute the desired action and provide other services as well. Manipulators used with
iostreams is an obvious example.
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30. 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.
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31. 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.
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32. 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.
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33. 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.
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34. 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 whe
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35. 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.
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36. What is slicing?
Answer: Slicing means that the data added by a subclass are discarded when an object of the subclass is passed or returned by value or from a function expecting a base class object.
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37. What is name mangling?
Answer: Name mangling is the process through which your c++ compilers give each function in your program a unique name. In C++, all programs have at-least a few functions with the same name. Name mangling is a concession to the fact that linker always insists on all function names being unique.
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38. What are proxy objects?
Answer: Objects that points to other objects are called proxy objects or surrogates. Its an
object that provides the same interface as its server object but does not have any
functionality. During a method invocation, it routes data to the true server object and
sends back the return value to the object.
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39. Differentiate between declaration and definition in C++.
Answer: A declaration introduces a name into the program; a definition provides a unique
description of an entity (e.g. type, instance, and function). Declarations can be repeated in
a given scope, it introduces a name in a given scope. There must be exactly one definition
of every object, function or class used in a C++ program.
A declaration is a definition unless:
Ø it declares a function without specifying its body,
Ø it contains an extern specifier and no initializer or function body,
Ø it i
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40. What is cloning?
Answer: An object can carry out copying in two ways i.e. it can set itself to be a copy of
another object, or it can return a copy of itself. The latter process is called cloning.
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41. Describe the main characteristics of static functions.
Answer: The main characteristics of static functions include,
Ø It is without the a this pointer,
Ø It can't directly access the non-static members of its class
Ø It can't be declared const, volatile or virtual.
Ø It doesn't need to be invoked through an object of its class, although for
convenience, it may.
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42. Will the inline function be compiled as the inline function always? Justify.
Answer: An inline function is a request and not a command. Hence it won't be compiled as an inline function always.
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43. Define a way other than using the keyword inline to make a function inline.
Answer: The function must be defined inside the class.
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44. How can a '::' operator be used as unary operator?
Answer: The scope operator can be used to refer to members of the global namespace.Because the global namespace doesnt have a name, the notation :: member-name refers to a member of the global namespace. This can be useful for referring to members of global namespace whose names have been hidden by names declared in nested local scope. Unless we specify to the compiler in which namespace to search for a declaration,the compiler simple searches the current scope, and any scopes in which the current scop
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45. What is placement new?
Answer: When you want to call a constructor directly, you use the placement new.
Sometimes you have some raw memory that's already been allocated, and you need to
construct an object in the memory you have. Operator new's special version placement
new allows you to do it.
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46. What is the difference between an object and a class?
Answer: All objects possessing similar properties are grouped into class.
Example :person is a class, ram, hari are objects of person class. All have similar attributes like name, age, sex and similar operations like speak, walk.
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47. What is a class?
Answer: The objects with the same data structure (attributes) and behavior (operations) are called class.
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48. What is an object?
Answer: It is an entity which may correspond to real-world entities such as students, employees, bank account. It may be concrete such as file system or conceptual such as scheduling policies in multiprocessor operating system.
Every object will have data structures called attributes and behavior called operations.
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49. What is the difference between class and structure?
Answer: In class the data members by default are private but in structure they are by default public.
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50. Define object based programming language?
Answer: Object based programming language support encapsulation and object identity without supporting some important features of OOPs language.
Object based language=Encapsulation + object Identity
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51. Define object oriented language?
Answer: Object-oriented language incorporates all the features of object based programming languages along with inheritance and polymorphism.
Example: c++, java.
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52. Define OOPs?
Answer: OOP is a method of implementation in which programs are organized as co-operative collection of objects, each of which represents an instance of some class and whose classes are all member of a hierarchy of classes united through the property of inheritance.
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53. What is public, protected, and private?
Answer: These are access specifier or a visibility lebels .The class member that has been declared as private can be accessed only from within the class. Public members can be accessed from outside the class also. Within the class or from the object of a class protected access limit is same as that of private but it plays a prominent role in case of inheritance
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54. What is a scope resolution operator?
Answer: The 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.
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55. What do you mean by inheritance?
Answer: The mechanism of deriving a new class (derived) from an old class (base class) is called inheritance. It allows the extension and reuse of existing code without having to rewrite the code from scratch.
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56. What is abstraction?
Answer: The technique of creating user-defined data types, having the properties of built-in data types and a set of permitted operators that are well suited to the application to be programmed is known as data abstraction. Class is a construct for abstract data types (ADT).
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57. What is encapsulation?
Answer: It is the mechanism that wraps the data and function it manipulates into single unit and keeps it safe from external interference.
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58. How variable declaration in c++ differs that in c?
Answer: C requires all the variables to be declared at the beginning of a scope but in c++ we can declare variables anywhere in the scope. This makes the programmer easier to understand because the variables are declared in the context of their use.
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59. What are the c++ tokens?
Answer: c++ has the following tokens
I. keywords
II. Identifiers
III. Constants
IV. Strings
V. operators
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60. What do you mean by reference variable in c++?
Answer: A reference variable provides an alias to a previously defined variable.
Data type & reference-name = variable name
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61. What do you mean by implicit conversion?
Answer: Whenever data types are mixed in an expression then c++ performs the conversion automatically.
Here smaller type is converted to wider type.
Example- in case of integer and float integer is converted into float type.
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62. What is the difference between method overloading and method overriding?
Answer: Overloading a method (or function) in C++ is the ability for functions of the same name to be defined as long as these methods have different signatures (different set of parameters). Method overriding is the ability of the inherited class rewriting the virtual method of the base class.
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63. What is polymorphism?
Answer: Polymorphism is the idea that a base class can be inherited by several classes. A base class pointer can point to its child class and a base class array can store different child class objects.
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64. What do you mean by inline function?
Answer: An inline function is a function that is expanded inline when invoked.ie. the compiler replaces the function call with the corresponding function code. An inline function is a function that is expanded in line when it is invoked. That is the compiler replaces the function call with the corresponding function code (similar to macro).
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65. What is the difference between a NULL pointer and a void pointer?
Answer: A NULL pointer is a pointer of any type whose value is zero. A void pointer is a pointer to an object of an unknown type, and is guaranteed to have enough bits to hold a pointer to any object. A void pointer is not guaranteed to have enough bits to point to a function (though in general practice it does).
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66. What do you mean by multiple inheritance in C++ ?
Answer: Multiple inheritance is a feature in C++ by which one class can be of different types. Say class teaching Assistant is inherited from two classes say teacher and Student.
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67. What do you mean by virtual methods?
Answer: virtual methods are used to use the polymorphism feature in C++. Say class A is inherited from class B. If we declare say function f() as virtual in class B and override the same function in class A then at runtime appropriate method of the class will be called depending upon the type of the object.
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68. What do you mean by static methods?
Answer: By using the static method there is no need creating an object of that class to use that method. We can directly call that method on that class. For example, say class A has static function f(), then we can call f() function as A.f(). There is no need of creating an object of class A.
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69. How many ways are there to initialize an int with a constant?
Answer: 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);
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70. What is a constructor?
Answer: Constructor is a special member function of a class, which is invoked automatically whenever an instance of the class is created. It has the same name as its class.
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71. What is destructor?
Answer: Destructor is a special member function of a class, which is invoked automatically whenever an object goes out of the scope. It has the same name as its class with a tilde character prefixed.
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72. What is an explicit constructor?
Answer: A conversion constructor declared with the explicit keyword. The compiler does not use an explicit constructor to implement an implied conversion of types. Its purpose is reserved explicitly for construction.
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73. What is the Standard Template Library?
Answer: 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.
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74. What problem does the namespace feature solve?
Answer: 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 librarys external declarations with a unique namespace that eliminates the potential for those collisions. This solution assumes that two library vendors dont use the same namespace identifier, of course.
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75. What is the use of ‘using declaration?
Answer: A using declaration makes it possible to use a name from a namespace
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76. What is a template?
Answer: Templates allow us to create generic functions that admit any data type as parameters and return a value without having to overload the function with all the possible data types. Until certain point they fulfill the functionality of a macro. Its prototype is any of the two following ones:
template function_declaration;
template function_declaration;
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77. Differentiate between a template class and class template?
Answer: Template class:
A generic definition or a parameterized class not instantiated until the client provides the needed information. Its jargon for plain templates.
Class template:
A class template specifies how individual classes can be constructed much like the way a class specifies how individual objects can be constructed. Its jargon for plain classes.
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78. What is the difference between a copy constructor and an overloaded assignment operator?
Answer: 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.
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79. What is a virtual destructor?
Answer: The simple answer is that a virtual destructor is one that is declared with the virtual attribute.
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80. What do you mean by Stack unwinding?
Answer: It is a process during exception handling when the destructor is called for all local objects between the place where the exception was thrown and where it is caught.
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81. What is a container class? What are the types of container classes?
Answer: A container class is a class that is used to hold objects in memory or external storage. A container class acts as a generic holder. A container class has a predefined behavior and a well-known interface. A container class is a supporting class whose purpose is to hide the topology used for maintaining the list of objects in memory. When a container class contains a group of mixed objects, the container is called a heterogeneous container; when the container is holding a group of objects that ar
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82. Name some pure object oriented languages?
Answer: Smalltalk, Java, Eiffel, Sather.
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84. What is an adaptor class or Wrapper class?
Answer: A class that has no functionality of its own. Its member functions hide the use of a third party software component or an object with the non-compatible interface or a non-object-oriented implementation.
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85. What is a Null object?
Answer: It is an object of some class whose purpose is to indicate that a real object of that class does not exist. One common use for a null object is a return value from a member function that is supposed to return an object with some specified properties but cannot find such an object.
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86. What is class invariant?
Answer: A class invariant is a condition that defines all valid states for an object. It is a logical condition to ensure the correct working of a class. Class invariants must hold when an object is created, and they must be preserved under all operations of the class. In particular all class invariants are both preconditions and post-conditions for all operations or member functions of the class.
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88. How can we access protected and private members of a class?
Answer: In the case of members protected and private, these could not be accessed from outside the same class at which they are declared. This rule can be transgressed with the use of the friend keyword in a class, so we can allow an external function to gain access to the protected and private members of a class.
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89. Can you handle exception in C++?
Answer: Yes we can handle exception in C++ using keyword: try, catch and throw. Program statements that we want to monitor for exceptions are contained in a try block. If an exception occurs within the try block, it is thrown (using throw).The exception is caught, using catch, and processed.
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90. What is virtual function?
Answer: A virtual function is a member function that is declared within a base class and
redefined by a derived class .To create a virtual function, the function declaration in the base class is preceded by the keyword virtual.
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91. What do you mean by early binding?
Answer: Early binding refers to the events that occur at compile time. Early binding occurs when
all information needed to call a function is known at compile time. Examples of early binding include normal function calls, overloaded function calls, and overloaded operators. The advantage of early binding is efficiency.
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92. what do you mean by late binding?
Answer: Late binding refers to function calls that are not resolved until run time. Virtual functions are used to achieve late binding. When access is via a base pointer or reference, the virtual function actually called is determined by the type of object pointed to by the pointer.
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