C++ Tutorial index

C++ Tutorial C++ History C++ installation C++ First Program C++ cin and cout C++ Data type C++ Variable C++ operator C++ Keywords C++ OOPS Concepts C++ Comments C++ Data Abstraction C++ Identifier C++ Memory Management C++ Storage Classes C++ Void Pointer C++ Array to function C++ Expressions C++ Features C++ Interfaces C++ Encapsulation

C++ Control Statements

C++ If C++ Nested if C++ If-else C++ If-else-if C++ Switch C++ Break C++ Continue C++ Goto C++ for loop C++ While loop C++ Do while loop

C++ functions

function in C++ C++ Call by Value C++ Call by Reference C++ Recursion function C++ inline function C++ Friend function C++ Friend functions function Pointer in C++ Sizeof() Operators in C++ C++ Math functions swap() function in C++ rand() and srand() in C / C++ wcscpy(), wcslen(), wcscmp() functions in C++ sort() function in C++ C++ vardiac() function System() function in C++ Fread function in C++ Programming Fscanf function in The C++ Gmtime function in C/C++ abs() function in C++ Sleep function in C++ Stoi function in C++ String erase() in C++ String Trim in C++ isprint() function in c++ is_trivial function in C++ div() function in C++ Set insert function in C++ rint(), rintf(), rintl() in C++ String append() function in C++ String push_back() in C++ String replace() in C++ Transform function in C++ exit() and _Exit() in C and C++ Std partition_point in C++ unique() in C++ ctime() function in C++ Gets() and Puts() in C++ Hypot(), hypotf() and hypotl() in C++ Log function in C++ Nearbyint() function in C++ setf() function in C++ Fill Function in C++ Map Find Function in C++ Malloc and Calloc in C++ Operator Function in C++ cin.get() in C++ seekp() Function in C++ eof() Function in C++ Emplace Back in C++ C++ macro function C_str in C++ Clock() in C/C++ round() function in C++ scalbn() function in C++ Stable Sort function in C++ Rotate in C++ Std:: Sort_heap in C++ Std::includes() in C++ STL std::memset() function in C++ Wcscmp() function in C++ Static Member function in C++ atof() function in C++ C++ Sin() function with Example cin.ignore() function in C++ Member function in C++ Pop_front Vector in C++ Vector resize() in C++ Malloc() and new in C++ std::distance in C++ C++ Date and Time fork() in C++ std::min in C++ isprint() in C++ rdbuf() in C++ fixed() Function in C++ setw() in C++ seekg() Function in C++ isdigit() Function in C++

C++ Function Miscellaneous

Precision of floating point numbers Using these functions floor(), ceil(), trunc(), round() and setprecision() in C++ function overloading in C++ Add two numbers using the function in C++ Advantage and disadvantage friend function C++ ATM machine program in C++ using functions Returning Multiple Values from a function using Tuple and Pair in C++ Find the Size of Array in C/C++ without using sizeof() function Pure Virtual function in C++ With Example Program Returning a function Pointer from a function in C/C++ Passing a Vector to a function in C++ functions in C++ With Types and Examples C++ Macro function Example Using Default Arguments with Virtual functions Virtual functions and Runtime Polymorphism Fesetround() and Fegetround() in C++ and their application Object as function Argument in C++ Private Member function in C++ Function Overriding in C++ C++ Program for Addition of Two Numbers Using functions function Object in C++ Elements of User Defined function in C++ Inline Functions in C++ Virtual Function in C++

C++ Arrays

Single dimension array Two dimension array

C++ Strings

C++ Strings

C++ Inheritance

C++ inheritance Single level inheritance Multilevel inheritance Multiple inheritance Hierarchical inheritance Hybrid inheritance

C++ Polymorphism

C++ Polymorphism C++ Overloading C++ Overriding C++ Virtual function

C++ Pointers

C++ Pointers C++ this pointer

C++ Exception Handling

C++ Exception Handling

C++ Constructors

C++ Constructors Default Constructor Parameterize Constructor Copy constructor Constructor Overloading Destructor

C++ File Handling

C++ File Handling C++ Writing to file C++ Reading file C++ Close file

C++ Programs

Structure of C++ Program Hello World Program in C++ C++ Program to Implement Shell Sort C++ Program to Implement Merge Sort C++ program to read string using cin.getline() C ++ Program: Alphabet Triangle and Number Triangle C++ Program: Matrix Multiplication C++ Program to Print Fibonacci Triangle C++ Program to find the product array puzzle C++ Program To Find Largest Subarray With 0 Sum C++ Program To Move All Zeros To The End of The Array C++ Program to find the element that occurs once C++ Program to find the largest number formed from an array Palindrome Number Program in C++ LCM Program in C++ Armstrong Number Program in C++ Factorial Program in C++ C++ Prime number program Program to convert infix to postfix expression in C++ Programs to Print Pyramid Patterns in C++ Array program in C++ Pattern programs in C++ Leap Year Program in C++ C++ Program for FCFS Depth First Search Program to Traverse a Graph in C++ inheritance Program in C++ Program that produces different results in C and C++ Example Program in C++ for input and Output Calculator Program using Switch in C++ Program for COPY Constructor in C++ Bank Program in C++ Anagram Program in C++

C++ Operators

Unary Operators in C++ Delete Operator in C++ C++ Bitwise XOR Operator Binary Operator Overloading in C++ Scope Resolution Operator in C++ C++ Ternary Operator New Operator in C++ Overloading array index operator in C++ Operator overloading in C++ Operators that cannot be overloaded in C++ Default Assignment Operator and References in C++ Conversion Operator in C++ Unary Operator Overloading in C++ Benefits of Operator Overloading in C++ Assignment Operator Overloading in C++ New and Delete Operator in C++ Insertion Operator in C++ Increment Operator in C++ Bitwise Operator in C++

C++ Examples

C++ Programming Examples While Loop Examples in C++ for Loop Examples in C++ Do-While Loop Examples in C++ SDL library in C++ with Examples C++ tcp client server example C++ tcp server example TCP Client Server Example in C++ Example of Parameterized Constructor in C++ Example of User Defined Data Type in C++

C++ Differences

C Vs C++ free() vs delete() in C++ Constructor Vs Destructor Passing by Reference Vs. Passing by the pointer in C++ C++ vs C# Structure Vs Class in C++ Virtual function Vs Pure Virtual function Structure Vs Class in C++ Exception Handling in C++ vs Java Static keyword in C++ vs Java inheritance in C++ vs Java C++ 11 vs C++ 14 vs C++ 17 Templates in C++ vs Generics in Java Bitwise Operator vs Logical Operator Type difference of Character literals in C VS C++ Copy Constructor vs Assignment Operator in C++ Map vs unordered_map in C++ Differences between #define & const in C/C++ Differences Between C Structures and C++ Structures Difference between Two Sets in C++ Difference between Exit and Return Differences between Local and Global Variable Difference between OOP and POP in C++ Difference between exit() and _Exit() in C++ Difference between int main() and int main(void) in C/C++ Difference Between Overloading and Overriding in C++ std::set_symmetric_difference in C++ Difference between Private and Protected in C++ Difference Between Encapsulation and Abstraction in C++ Difference between Template and Macro in C++ Difference between Abstraction and Interface in C++ Differences Between C++ and Javascript Difference between POP and OOP in C++

How To

How to concatenate two strings in C++ How to Reverse a String in C++ using Do-While Loop How to Reverse a String in C++ using for Loop How to Reverse a String in C++ using While Loop How to create a table in C++ How to Setup Environment for C++ Programming on Mac How to call a void function in C++ How to create a directory or folder in C/C++ How to create a library in C++ How to create a stack in C++ How to create the Processes with fork in C++ How to Handle Divide by Zero Exception in C++ How to Declare Unordered Sets in C++ How to Sort an Array in C++ How to run program in turbo c++ How to Use Getline in C++ How is Multiset Implemented in C++ How to Build a Program in C++ How to Declare a 2d Array Dynamically in C++ How to create a button in C++ How the value is passed in C++ How to calculate size of string in C++ How to convert binary string to int in C++ How to convert string to float in C++ How to remove space from string in C++ How to use pair in C++ How to use the string find() in C++ How to Remove an Element From an Array in C++ How to Take Space Separated input in C++ How to Copy in Turbo C++ How to Use Pow in C++ How to Use Set in C++ How to Create Singleton Class in C++ How to Allocate Memory Dynamically in C++ How to Close Turbo C++ in Windows 10 How to Use Modulus in C++

C++ Questions

What does Buffer Flush mean in C++ What is endl in C++ What is Unary Operator Overloading in C++ Which operators cannot be overloaded in C++ What is Static Member function in C++ What is This Pointer in C++ What is Upcasting in C++ What Kind of Exceptions Are Available in C++ What is Memory Allocation for Objects in C++ What is a Linked List in C++ is assignment operator inherited in C++ When should we write own Assignment operator in C++ What is an Object in C++ What is Copy Constructor in C++ What is a Static Member Function in C++

C++ Interview Questions

Advanced C++ interview Questions Oops Interview Questions in C++

Miscellaneous

External merge sort in C++ Remove duplicates from sorted array in C++ C++ References C++ Mutable keyword initialize Array of objects with parameterized constructors in C++ Storage Classes in C goto statement in C and C++ C++ String Concatenation Heap Sort in C++ Swap numbers in C++ input Iterators in C++ Fibonacci Series in C++ Stack in C++ Maps in C++ Queue in C++ C++ Bitset C++ Algorithms Priority Queue in C++ C++ Multimap C++ Deque C++ array of Pointers Timsort Implementation Using C++ CPP Templates C++ Aggregation C++ Enumeration C++ Object Class C++ Queue initialize Vector in C++ Vector in C++ C++ STL Components C++ Maximum index Problem C++ find missing in the second array C++ Namespaces C++ OOPs Concept C++ Static C++ Structs C++ Try-Catch C++ User Defined Exceptions C++ Virtual Destructor Snake Code in C++ Splitting a string in C++ C++ Bidirectional Iterators C++ forward Iterators C++ Iterators C++ Output Iterators C++ Range-based for Loop Converting string into integer in C++ Type conversion in C++ Binary to Decimal in C++ Bit Manipulation in C++ C++ Constructor C++ Dijkstra Algorithm Using the Priority Queue C++ int into String C++ Signal Handling Decimal to Binary in C++ Decimal to Hexadecimal in C++ Decimal to Octal in C++ Hexadecimal to Decimal in C++ Octal to Decimal in C++ Reverse a Number in C++ C++ forward Iterators C++ Output Iterators Char Array to String in C++ Constructor Overloading in C++ Default arguments in C++ Different Ways to Compare Strings in C++ Dynamic Binding in C++ SET Data Structure in C++ Upcasting and Downcasting in C++ Reverse an Array in C++ Fast input and Output in C++ Copy elision in C++ Array of sets in C++ Binary Search in C++ Implementing the sets without C++ STL containers Smart pointers in C++ Types of polymorphism in C++ Const Keyword in C++ Type Casting in C++ Stringstream in C++ and its applications C++ Scope of Variables Star pattern in C++ using for Loops Top 5 IDEs for C++ That You Should Try Once Assertions in C/C++ C++ Convert int to String Continue in C++ While loop Diamond Pattern in C++ using for Loop infinite loop in C++ Loops in C++ Auto keyword in C++ C++ STL (Standard Template Library) Divide by Zero Exception in C++ Dynamic Constructor in C++ Dynamic Memory Allocation in C++ Floating Point Operations and Associativity in C, C++ and Java Implementation of a Falling Matrix in C++ Message Passing in C++ Pointer to Object in C++ Ways to Copy a Vector in C++ Structure Sorting (By Multiple Rules) in C++ Similarities between C++ and Java C++ Tricks for Competitive Programming Desired Capabilities in Selenium Web Driver in C++ Socket Programming in C++ Template Specialization in C++ Classes and Objects in C++ Convex hull Algorithm in C++ DES in C++ Structured Binding in C++ Functors in C++ Lambda Expression in C++ Roadmap to C++ Programming Substring in C++ Virtual base class in C++ Bits stdc++.h in C++ Top 14 Best Free C++ IDE (Editor & Compiler) for Windows in 2022 Bitmasking in C++ Features of OOPS in C++ Hospital Management Project in C++ include Guards in C++ Iostream in C++ Method overriding in C++ Naming Convention in C++ Nullptr in C++ Object Slicing in C++ Principles of Object-Oriented Programming in C++ Processing strings using std string stream in C++ Random Number Generator in C++ Singleton Design Pattern in C++ Size_t Data Type in C++ Skyline Problem in C++ Web Development in C++ Data Hiding in C++ Hashing in C++ Object in C++ Sum of all Elements between k1’th and k2’th Smallest Elements Virtual class in C++ Vector Size in C++ Top best IDEs for C/C++ Developers in 2022 Tensorflow in C++ Sliding Window Technique in C++ Reverse String Word-Wise in C++ RTTI in C++ Pthreads or POSIX Threads in C++ Reserved Keywords in C++ 10 Best C and C++ Books for Beginners & Advanced Programmers Add two numbers represented by two arrays in C++ Array of Object in C++ Containership in C++ Counting Frequencies of Array Elements in C++ Decltype type Specifier in C++ Dynamic _Cast in C++ Features and Use of Pointers in C/C++ int Max and int Min in C/C++ is It Fine to Write Void Main Or Main in C/C++ Compile Time Polymorphism in C++ Division in C++ Factorial of a Number in C++ using while Loop Multiset in C++ 4 Pillars of OOPs Approach in C++ Backtracking Time Complexity in C++ C++ Global Variable C++ Pipe Tutorial Observer Design Pattern in C++ Private inheritance in C++ Pthread in C++ Parameters Pointers in C++ Abstract Factory Design Pattern in C++ Ascending order in C++ Call by Pointer in C++ Constexpr in C++ Deadlock in C++ Design Patterns in C++ Factory Method for Designing Pattern in C++ Name Mangling and extern in C++ Preventing Object Copy in C++ Quick Sort in C++ Single Handling in C++ Use of inheritance in C++ User-defined literals in C++ Vector methods in C++ Void * in C and C++ Zombie and Orphan Process in C++ List and Vector in C++ List iterators in C++ Merging Two Vectors in C++ Early Binding and Late Binding in C++ Factory Design Pattern in C++ Fisher-Yates shuffle algorithm in C++ for Auto in C++ Group anagrams in C++ Dynamic Casting in C++ 2D Vector initialization in C++ C++ GUI Visual Studio C++ IPC C++ Permutation Overloading Stream insertion in C++ Array sum in C++ STL C++ Define Macro C++ Design C++ Factory Pattern Convert String to Uppercase in C++ initializer list in C++ Iterator invalidation in C++ Lower bound in C++ Modulus of Two float numbers or double number Pass by value in C++ Stack size in C++ Unordered_map in C++ Binary String to int C++ Boost C++ Exception handling in constructor and destructor in C++ Explain class template in C++ Kadane Algorithm in C++ Map of Pairs in STL Pair in C++ Access Specifiers in C++ Add Two Numbers in C++ Using Class C++ Socket Programming Windows Cube root in C++ C++ Protected inheritance C++ Return Object Static Data Members in C++ Association in C++ Boost libraries in C++ Automatic Storage Class in C++ C++ Move Constructor Cast in C++ C++ 11 Lambda C++ Multithreading Bottom-up Approach in C++ C++ Static Class C++ Static Member C++ Static Variable C++ Template Class Implementation Kruskals Algorithm in C++ Kth Permutation Sequence in C++ Kth Smallest Element Using Priority Queue in C++ Min Heap in C++ Multilevel inheritance in C++ Playfair Cipher Algorithm in C++ Exception Handling in Java and C++ Sorting in C++ Time and Space Complexity for Loops in C++ Convert Vector To String in C++ Cascading in C++ Control Structure in C++ Passing Object as argument in C++ Vector Pair in C++ String Data Types in C++ Topological Sort in C++ C++ Move Semantics C++ Static Library Linking Call by Value and Call by Reference in C++ Data Structures algorithms and application in C++ Dereferencing a Pointer in C++ Linked List in C++ All Swing Components in C++ anonymous Object in C++ Cerr in C++ Control Flow Statement in C++ cstdlib in C++ Exception Objects in C++ Base Class and Derived Class in C++ Creating A Menu in C++ Escape Sequence in C++ Explicit in C++ int range in C++ Maximum Value in Vector in C++ NPTEL Programming in C++ Shared Pointer in C++ Static Member Function in C++ With Example The Diamond Pattern in C++ Const ptr C++ Const_Cast C++ Area Of Triangle in C++ Array input in C++ Cin String in C++ Coroutine in C++ Gui Design in C++ integer in C++ Advantages and Disadvantages of inheritance in C++ C++ IDE Linux C++ Mini Project With Source Code And Output C++ Variables Types Containers in C++ Dynamic Binding in C++ Explain Access Specifiers in C++ Iomanip in C++ Noexcept in C++ C++ Reference Initializer in C++ Constant Arguments in C++ Vector in C++ Stl Singleton Pattern in C++ Error Handling in C++ C++ Thread Id to Int C Str in C++ C++ Shared Ptr Scope Resolution Operator in C++ C++ Random Number Between 1 and 10 File Opening Mode in C++ New and Delete in C++ Big Integers in C++ Stack Unwinding in C++ C++ Syntax Link Map cbegin() and cend() function in C++ STL Hamming Code Implementation in C++ Files and Streams in C++ Private Destructor in C++ Semaphore in C++ Map Emplace_hint() function in C++ STL Complex Number Program in C++ Meta Classes in C++ C++ Delegates Custom Sort in C++ RAII in C++ Babylonian Square Root Algorithm in C++ File Input and output operation in C++ Sum of Digits of a Number in C++ C++ Type Traits Binary Search Tree Program in C++ Tree in C++ Built in Types in C++ Catch all Exceptions in C++ C++ Template Class Declaration and Definition C++ Generic Programming Introduction Fundamental Data Types in C++ API in C++ Menu Driven Program in C++ Exception Specification in C++ Bit Manipulation in C++ Dynamic Initialization Of Objects in C++ Returning Object from a Function in C++ Class and Structure in C++ Edmonds Karp Algorithm in C++ Flush in C++ Find Substring in C++ Input and Output Operators in C++ Final in C++ Lvalue and Rvalue in C++ C++ Singleton File Stream in C++ Has a Relationship in C++ Character Set in C++ Menu Driven Program in C++ Final Keyword in C++ Associative Containers in C++ Decltype in C++ Insert Function in C++ Metaclass in C++ Move Constructor in C++ Move Semantics in C++

C++ storage classes

Storage Classes are used to characterize a variable's or function's characteristics. These characteristics include scope, visibility, and life-time, which allow us to track the presence of a variable over the course of a program's execution. The following syntax is used to indicate the storage class for a variable:

Syntax: 

storage_class-name variable_data_type variable_name;

C++ has five different storage classes:

  • Auto
  • Register
  • Extern
  • Static
  • Mutable
C++ Storage Classes

Auto Storage Class:

The auto keyword allows for type inference, which allows for the automated determination of the data type of an expression in a programming language. This saves time by eliminating the need to type down information that the compiler already has. Because all types are inferred in the compiler phase alone, the compilation time increases somewhat but has no effect on the program's execution time. This functionality also applies to non-type template arguments and functions. Since C++14, the return type of a function may be derived from its return statements. Since C++17, the type of non-type template parameters is derived from the argument.

Example-

{
 int date;
 auto int date;
}

In the example above, two variables ie. date with the same storage class are defined; nevertheless, auto may only be used within functions, i.e., local variables.

Register Storage Class:

Local variables that should be saved in a register rather than RAM are defined using the register storage class. This indicates that the variable's maximum size is equal to the register size (typically one word) and that it cannot be used with the unary '&' operator (as it does not have a memory location).

Example –

{
 register int distance;
}

Here in this example, we have used keyword register to save the int variable date in it.

We use the register only for variables that require immediate access, such as counters. It's also worth noting that just because 'register' is defined doesn't ensure the variable will be put in a register. It signifies that, depending on hardware and implementation constraints, it MIGHT be saved in a register.

Static Storage Class:

The static storage class tells the compiler to keep a local variable alive for the duration of the programme, rather than creating and deleting it every time it enters and exits scope. As a result, making local variables static ensures that their values are preserved across function calls.

The static modifier may be used on global variables as well. When you do this, the scope of that variable is limited to the file in which it is defined.

When the static keyword is used to a class data member in C++, only one copy of that member is shared by all objects in that class.

Example –

#include <iostream>
using namespace std;
// Function having static variables
int staticFunc()
{
cout << "For static vars: ";
static int counting = 0;
counting++;
return counting;
}
// Function having non-static variables
int nonStaticFunc()
{
cout << "For Non-Static vars: ";
int counting = 0;
counting++;
return counting;
}
int main()
{
// Calling static parts
cout << staticFunc() << "\n";
cout << staticFunc() << "\n";
;
// Calling non-static parts
cout << nonStaticFunc() << "\n";
;
cout << nonStaticFunc() << "\n";
;
return 0;
}

Output:

For static vars: 1
For static vars: 2
For non-static vars: 1
For non-static vars: 1

In this example, we created a function staticFunc() having static variables. In that we applied a loop to count the no. of times it’s executed. Then we did the same for the non-static variables using the function called nonStaticFunc(). Then we initialised the main code and called the staticFunc() to print its values first and then the nonStaticFunc(). Thus we got the required output.

Extern Storage Class:

It's used to refer to a global variable that's viewable across all programme files. When you use 'extern,' the variable cannot be initialised since all it does is refer the variable name to a previously determined storage address.

When you have many files and you specify a global variable or function that will be used in other files as well, you'll utilise extern to offer a reference to the specified variable or function in another file. Simply said, extern is used in another code to define a global variable or function.

When two or more files share the same global variables or functions, the extern modifier is most usually used, as detailed below.

Example -

#include <iostream>
using namespace std;
// declared variable that is to be made extern
//initial value initialized to z
int z;
void externClass()
{
cout << "Showing extern class\n";
// briefing compiler that var
// z is extern var and has been
// defined elsewhere
extern int z;
// printing 'z'
cout << "The Value of var 'z'"
<< "that is declared as extern: " << z << "\n";
// value of extern var z modifying now
x = 5;
// printing modified values
cout
<< "Modified value of 'z'"
<< " that is declared as extern: \n"
<< z;
}
int main()
{
externClass();
return 0;
}

Output:

Showing extern class
The Value of var 'z' that is declared as extern: 0
Modified value of 'z' that is declared as extern: 5

In this example, we first declared a variable that is to be made external and initialized the int value to z. We created a function externClass() to show the external class present. Using extern keyword we briefed the compiler that the variable z is external variable and has been defined somewhere else and not in that class. First printed the value of external variable z and then modified its value and printed that. Finally executed the function in the int main and got the desired output.

Mutable Storage Class:

Only class objects are affected by the mutable specifier, which will be explored later in this article. It allows an object member to override the constant member function. That is, a constant member function can modify a mutable member.

#include <iostream>
using std::cout;
class Testing {
public:
int a;
mutable int b;
Test() { a = 4; b = 10; }
};
int main()
{
const Testing t1;
t1.b = 20;
cout << t1.b;
return 0;
}

Output:

20

In this Example, we created a class named Testing in public form and gave variables a and b and used b as mutable variable using keyword mutable. Then used the Testing class in main to generate the given value of mutable variable.

Storage Classes are used to characterize a variable's or function's characteristics. These characteristics include scope, visibility, and life-time, which allow us to track the presence of a variable over the course of a program's execution. The following syntax is used to indicate the storage class for a variable:

Syntax: 

storage_class-name variable_data_type variable_name;

C++ has five different storage classes:

  • Auto
  • Register
  • Extern
  • Static
  • Mutable
C++ Storage Classes

Auto Storage Class:

The auto keyword allows for type inference, which allows for the automated determination of the data type of an expression in a programming language. This saves time by eliminating the need to type down information that the compiler already has. Because all types are inferred in the compiler phase alone, the compilation time increases somewhat but has no effect on the program's execution time. This functionality also applies to non-type template arguments and functions. Since C++14, the return type of a function may be derived from its return statements. Since C++17, the type of non-type template parameters is derived from the argument.

Example-

{
 int date;
 auto int date;
}

In the example above, two variables ie. date with the same storage class are defined; nevertheless, auto may only be used within functions, i.e., local variables.

Register Storage Class:

Local variables that should be saved in a register rather than RAM are defined using the register storage class. This indicates that the variable's maximum size is equal to the register size (typically one word) and that it cannot be used with the unary '&' operator (as it does not have a memory location).

Example –

{
 register int distance;
}

Here in this example, we have used keyword register to save the int variable date in it.

We use the register only for variables that require immediate access, such as counters. It's also worth noting that just because 'register' is defined doesn't ensure the variable will be put in a register. It signifies that, depending on hardware and implementation constraints, it MIGHT be saved in a register.

Static Storage Class:

The static storage class tells the compiler to keep a local variable alive for the duration of the programme, rather than creating and deleting it every time it enters and exits scope. As a result, making local variables static ensures that their values are preserved across function calls.

The static modifier may be used on global variables as well. When you do this, the scope of that variable is limited to the file in which it is defined.

When the static keyword is used to a class data member in C++, only one copy of that member is shared by all objects in that class.

Example –

#include <iostream>
using namespace std;
// Function having static variables
int staticFunc()
{
cout << "For static vars: ";
static int counting = 0;
counting++;
return counting;
}
// Function having non-static variables
int nonStaticFunc()
{
cout << "For Non-Static vars: ";
int counting = 0;
counting++;
return counting;
}
int main()
{
// Calling static parts
cout << staticFunc() << "\n";
cout << staticFunc() << "\n";
;
// Calling non-static parts
cout << nonStaticFunc() << "\n";
;
cout << nonStaticFunc() << "\n";
;
return 0;
}

Output:

For static vars: 1
For static vars: 2
For non-static vars: 1
For non-static vars: 1

In this example, we created a function staticFunc() having static variables. In that we applied a loop to count the no. of times it’s executed. Then we did the same for the non-static variables using the function called nonStaticFunc(). Then we initialised the main code and called the staticFunc() to print its values first and then the nonStaticFunc(). Thus we got the required output.

Extern Storage Class:

It's used to refer to a global variable that's viewable across all programme files. When you use 'extern,' the variable cannot be initialised since all it does is refer the variable name to a previously determined storage address.

When you have many files and you specify a global variable or function that will be used in other files as well, you'll utilise extern to offer a reference to the specified variable or function in another file. Simply said, extern is used in another code to define a global variable or function.

When two or more files share the same global variables or functions, the extern modifier is most usually used, as detailed below.

Example -

#include <iostream>
using namespace std;
// declared variable that is to be made extern
//initial value initialized to z
int z;
void externClass()
{
cout << "Showing extern class\n";
// briefing compiler that var
// z is extern var and has been
// defined elsewhere
extern int z;
// printing 'z'
cout << "The Value of var 'z'"
<< "that is declared as extern: " << z << "\n";
// value of extern var z modifying now
x = 5;
// printing modified values
cout
<< "Modified value of 'z'"
<< " that is declared as extern: \n"
<< z;
}
int main()
{
externClass();
return 0;
}

Output:

Showing extern class
The Value of var 'z' that is declared as extern: 0
Modified value of 'z' that is declared as extern: 5

In this example, we first declared a variable that is to be made external and initialized the int value to z. We created a function externClass() to show the external class present. Using extern keyword we briefed the compiler that the variable z is external variable and has been defined somewhere else and not in that class. First printed the value of external variable z and then modified its value and printed that. Finally executed the function in the int main and got the desired output.

Mutable Storage Class:

Only class objects are affected by the mutable specifier, which will be explored later in this article. It allows an object member to override the constant member function. That is, a constant member function can modify a mutable member.

#include <iostream>
using std::cout;
class Testing {
public:
int a;
mutable int b;
Test() { a = 4; b = 10; }
};
int main()
{
const Testing t1;
t1.b = 20;
cout << t1.b;
return 0;
}

Output:

20

In this Example, we created a class named Testing in public form and gave variables a and b and used b as mutable variable using keyword mutable. Then used the Testing class in main to generate the given value of mutable variable.