C++ interview questions and answers

C is procedural.

Encapsulation, abstraction, inheritance, and polymorphism.

Stack holds locals and is freed when the function returns

A pointer can be null and can be reseated.

New allocates on the heap and calls constructors.

A constructor sets up the object when it is created.

The only language difference is default access: public for struct, private for class.

Overloading is same name, different parameters, resolved at compile time.

If the destructor is not virtual, only the base destructor runs and the derived cleanup is skipped.

It enables dynamic dispatch through a vtable so the derived method runs on a base pointer.

Ifndef define endif, or pragma once, stops a header from being included twice in one translation unit.

It groups names to avoid clashes, like std.

A const member function promises not to mutate the object, so it can be called on a const instance.

Vector is a dynamic array: contiguous, O(1) index, amortized push_back.

List is a doubly linked list: stable iterators on insert, but poor cache use and no random access.

By value copies

A class with at least one pure virtual function, written as virtual f() = 0.

The standard gives no requirements, so the compiler may do anything: use-after-free, signed overflow, out-of-bounds.

If I write a destructor, copy constructor, or copy assignment, I likely need all three.

Resource acquisition is initialization: the constructor takes the resource, the destructor releases it.