Once you’ve learned the basics of C++, it’s time to go deeper. These advanced C++ interview questions help you understand concepts that real companies test during coding interviews.
Let’s learn them in simple and clear language 👇

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1. What are pointers in C++ and why are they used?

Answer:
A pointer is a variable that stores the memory address of another variable.
It helps in dynamic memory allocation, passing large data efficiently, and building data structures like linked lists.

Example:

int a = 10;
int* ptr = &a;
cout << "Value: " << *ptr; // Output: 10

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2. What is dynamic memory allocation in C++?

Answer:
Dynamic memory allocation means assigning memory at runtime instead of compile-time.
In C++, we use new and delete operators for this.

Example:

int* num = new int(5);
cout << *num;   // 5
delete num;     // free memory

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3. What is the difference between shallow copy and deep copy?

Type	Description
Shallow Copy	Copies only the pointer, not the actual data.
Deep Copy	Creates a new copy of the data as well.

Example:

class Demo {
    int* data;
public:
    Demo(int val) { data = new int(val); }
    // Deep copy constructor
    Demo(const Demo &d) { data = new int(*d.data); }
};

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4. What is the difference between reference and pointer in C++?

Feature	Pointer	Reference
Reassignment	Can be reassigned	Cannot be reassigned
Null	Can be null	Cannot be null
Syntax	Uses * and &	Uses & only

Example:

int a = 5;
int* ptr = &a;
int& ref = a;

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5. What are virtual destructors in C++?

Answer:
A virtual destructor ensures the derived class destructor runs when deleting an object through a base class pointer.
Without it, only the base destructor executes — causing memory leaks.

Example:

class Base {
public:
    virtual ~Base() { cout << "Base destroyed\n"; }
};
class Derived : public Base {
public:
    ~Derived() { cout << "Derived destroyed\n"; }
};

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6. What is the difference between abstract class and interface in C++?

Answer:
C++ doesn’t have a direct “interface” keyword, but we can create it using pure virtual functions.

Feature	Abstract Class	Interface
Methods	Can have normal and pure virtual functions	All pure virtual functions
Data	Can have data members	No data members

Example:

class Interface {
public:
    virtual void show() = 0;  // pure virtual
};

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7. What are pure virtual functions?

Answer:
A pure virtual function is declared but not defined in the base class.
It forces derived classes to provide their own implementation.

Syntax:

virtual void functionName() = 0;

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8. What is multiple inheritance in C++?

Answer:
Multiple inheritance allows a class to inherit from more than one base class.

Example:

class A { };
class B { };
class C : public A, public B { };

👉 However, it may cause ambiguity, known as the Diamond Problem, which can be resolved using virtual inheritance.

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9. What is the Diamond Problem in C++?

Answer:
When two base classes inherit from the same grandparent class, and a derived class inherits from both, it creates ambiguity.
To fix this, use virtual base classes.

Example:

class A { public: void show() { cout << "A"; } };
class B : virtual public A { };
class C : virtual public A { };
class D : public B, public C { };

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10. What are friend functions in C++?

Answer:
A friend function is not a member of a class but can access its private and protected data.
It’s declared using the friend keyword.

Example:

class Box {
private:
    int width;
public:
    friend void printWidth(Box b);
};

void printWidth(Box b) {
    cout << b.width;
}

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11. What is function overriding?

Answer:
Function overriding allows a derived class to redefine a base class method.
The function must have the same name, parameters, and return type.

Example:

class Base {
public:
    virtual void show() { cout << "Base"; }
};
class Derived : public Base {
public:
    void show() override { cout << "Derived"; }
};

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12. What is the difference between ‘new/delete’ and ‘malloc/free’?

Feature	new/delete	malloc/free
Type Safety	Type safe	Not type safe
Constructor/Destructor	Called automatically	Not called
Operator/Function	Operator	Function

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13. What is an inline function?

Answer:
Inline functions suggest the compiler to insert the function code directly at the place of the function call to reduce function call overhead.

Example:

inline int square(int x) { return x * x; }

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14. What is the difference between stack and heap memory?

Feature	Stack	Heap
Managed by	Compiler	Programmer
Lifetime	Ends when function ends	Until manually freed
Speed	Faster	Slower

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15. What is an iterator in C++ STL?

Answer:
An iterator is an object that points to elements inside containers like vector, list, or map.
It behaves like a pointer.

Example:

#include <vector>
#include <iostream>
using namespace std;

int main() {
    vector<int> v = {10, 20, 30};
    for (auto it = v.begin(); it != v.end(); ++it)
        cout << *it << " ";
}

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16. What is a lambda function in C++?

Answer:
Lambda functions are anonymous functions defined within code blocks.
They’re useful for short tasks.

Example:

auto add = [](int a, int b) { return a + b; };
cout << add(3, 5);

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17. What is smart pointer in C++?

Answer:
Smart pointers are objects that automatically manage memory. They delete the object when no longer used.

Types:

• unique_ptr — owns one object only
• shared_ptr — shared ownership
• weak_ptr — non-owning reference

Example:

#include <memory>
using namespace std;

int main() {
    unique_ptr<int> p = make_unique<int>(10);
    cout << *p;
}

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18. What is move semantics in C++11?

Answer:
Move semantics allow resources to be transferred from one object to another instead of copying, improving performance.

Example:

string s1 = "Hello";
string s2 = move(s1);

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19. What are function templates and class templates?

Answer:
Templates help write generic code.

Function Template:

template <typename T>
T add(T a, T b) { return a + b; }

Class Template:

template <class T>
class Box {
    T value;
public:
    Box(T v) : value(v) {}
};

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20. What are STL containers?

Answer:
STL containers store collections of data.
Main types:

• Sequence Containers: vector, list, deque
• Associative Containers: map, set
• Unordered Containers: unordered_map, unordered_set

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21. What is the difference between map and unordered_map?

Feature	map	unordered_map
Order	Sorted	Unsorted
Time Complexity	O(log n)	O(1) average
Implementation	Red-black tree	Hash table

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22. What is the difference between const and constexpr?

Keyword	Meaning
const	Value can’t change after initialization
constexpr	Evaluated at compile-time

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23. What is RTTI (Run-Time Type Information)?

Answer:
RTTI allows finding the type of an object at runtime using operators like typeid and dynamic_cast.

Example:

Base* b = new Derived();
cout << typeid(*b).name();

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24. What is the difference between pass by value and pass by reference?

Type	Description
Pass by Value	A copy of data is passed; changes don’t affect original
Pass by Reference	Original data is passed; changes affect original

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25. What is the difference between static and dynamic binding?

Binding Type	When Decided	Example
Static	Compile-time	Function overloading
Dynamic	Run-time	Virtual functions

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✅ Final Tips for Freshers

• Practice STL and smart pointers.
• Revise OOPs and templates carefully.
• Understand memory management concepts.
• Write small code snippets to test yourself daily.

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