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++ 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

C++ Call by Value C++ Call by Reference C++ Recursion Function C++ Inline function C++ Friend function

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

Miscellaneous

C Vs C++ 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 std::min in C++ External merge sort in C++ Remove duplicates from sorted array in C++ Precision of floating point numbers Using these functions floor(), ceil(), trunc(), round() and setprecision() in C++ C++ References C++ Friend Functions C++ Mutable keyword Unary Operators in C++ Initialize Array of objects with parameterized constructors in C++ Differences between #define & const in C/C++ C++ Program to Implement Shell Sort C++ Program to Implement Merge Sort Storage Classes in C Vector resize() in C++ Passing by Reference Vs. Passing by the pointer in C++ Free vs delete() in C++ goto statement in C and C++ C++ program to read string using cin.getline() C++ String Concatenation Heap Sort in C++ Swap numbers in C++ Input Iterators in C++ Fibonacci Series in C++ C ++ Program: Alphabet Triangle and Number Triangle C++ Program: Matrix Multiplication C++ Program to Print Fibonacci Triangle Stack in C++ Maps in C++ Queue in C++ C++ Bitset C++ Algorithms Priority Queue in C++ C++ Multimap C++ Deque Function Pointer in C++ Sizeof() Operators in C++ C++ array of Pointers free() Vs delete in C Timsort Implementation Using C++ CPP Templates C++ Aggregation C++ Enumeration C++ Math Functions C++ Object Class C++ Queue Initialize Vector in C++ Vector in C++ C++ STL Components Function overloading in C++ C++ Maximum Index Problem C++ find missing in the second array 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 Constructor Vs Destructor C++ Namespaces C++ OOPs Concept C++ Static C++ Structs C++ Try-Catch C++ User Defined Exceptions C++ Virtual Destructor C++ vs C# Malloc() and new in C++ Palindrome Number Program in C++ Snake Code in C++ Splitting a string in C++ Structure Vs Class in C++ Virtual Function Vs Pure Virtual Function C++ Bidirectional Iterators C++ Forward Iterators C++ Iterators C++ Output Iterators C++ Range-based For Loop Converting string into integer in C++ LCM Program in C++ Type conversion in C++ Add two numbers using the function in C++ Advantage and disadvantage friend function C++ Armstrong Number Program in C++ ATM machine program in C++ using functions 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++ Factorial Program in C++ Function in C++ Hexadecimal to Decimal in C++ Octal to Decimal in C++ Reverse a Number in C++ Structure Vs Class in C++ C++ Forward Iterators C++ Output Iterators C++ Prime number program 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++ Program to convert infix to postfix expression in C++ SET Data Structure in C++ Upcasting and Downcasting in C++ Reverse an Array in C++ Fast Input and Output in C++ Delete Operator in C++ Copy elision in C++ C++ Date and Time C++ Bitwise XOR Operator Array of sets in C++ Binary Operator Overloading in C++ Binary Search in C++ Implementing the sets without C++ STL containers Scope Resolution Operator in C++ Smart pointers in C++ Types of polymorphism in C++ Exception Handling in C++ vs Java Const Keyword in C++ Type Casting in C++ Static keyword in C++ vs Java Inheritance in C++ vs Java How to concatenate two strings in C++ Programs to Print Pyramid Patterns in C++ swap() function in C++ Structure of C++ Program Stringstream in C++ and its applications rand() and srand() in C / C++ C++ Ternary Operator C++ Scope of Variables While Loop Examples in C++ Star pattern in C++ using For Loops For Loop Examples in C++ Do-While Loop Examples in C++ 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 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 Infinite loop in C++ Loops in C++ Returning Multiple Values from a Function using Tuple and Pair in C++ wcscpy(), wcslen(), wcscmp() Functions in C++ Auto keyword in C++ C++ 11 vs C++ 14 vs C++ 17 C++ STL (Standard Template Library) Differences Between C Structures and C++ Structures Divide by Zero Exception in C++ Dynamic Constructor in C++ Dynamic Memory Allocation in C++ Find the Size of Array in C/C++ without using sizeof() function Floating Point Operations and Associativity in C, C++ and Java Hello World Program in C++ How to create a table in C++ How to Setup Environment for C++ Programming on Mac Implementation of a Falling Matrix in C++ Message Passing in C++ Pointer to Object in C++ Templates in C++ vs Generics in Java Ways to Copy a Vector in C++ What does Buffer Flush mean in C++ sort() function in C++ Structure Sorting (By Multiple Rules) in C++ Similarities between C++ and Java std::distance in C++ Array program in C++ 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++ C++ vardiac() function Difference between Two Sets in C++ Difference between Exit and Return Structured Binding in C++ Differences between Local and Global Variable Bitwise Operator vs Logical Operator Difference between OOP and POP in C++ Fork in C++ Functors in C++ 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++ Lambda Expression in C++ Pattern programs 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++ Auto Keyword in C++ Features of OOPS in C++ Hospital Management Project in C++ How to Declare Unordered Sets in C++ How to Sort an Array in C++ Include Guards in C++ Iostream in C++ Method overriding in C++ How to run program in turbo c++ How to Use Getline in C++ Leap Year Program in C++ Naming Convention in C++ New Operator in C++ Nullptr in C++ Object Slicing in C++ Principles of Object-Oriented Programming in C++ Processing strings using std string stream in C++ Pure Virtual Function in C++ With Example Program Random Number Generator in C++ Singleton Design Pattern in C++ Size_t Data Type in C++ Skyline Problem in C++ System() function in C++ Web Development in C++ Data Hiding in C++ Difference between exit() and _Exit() 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++ Returning a Function Pointer from a Function in C/C++ RTTI in C++ Pthreads or POSIX Threads in C++ Reserved Keywords in C++ Passing a Vector to a function 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++ C++ Program For FCFS Containership in C++ Counting Frequencies of Array Elements in C++ Decltype type Specifier in C++ Dynamic _Cast in C++ Difference between int main() and int main(void) in C/C++ Depth First Search Program to Traverse a Graph in C++ Features and Use Of Pointers in C/C++ Fread Function in C++ Programming Fscanf Function in The C++ Functions in C++ With Types and Examples Gmtime Function in C/C++ How is Multiset Implemented in C++ How to Build a Program in C++ How to Declare a 2d Array Dynamically in C++ inheritance Program in C++ int Max and int Min in C/C++ is It Fine to Write Void Main Or Main in C/C++ How to create a button in C++ abs() function in 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 SDL library in C++ with Examples Pointers in C++ Abstract Factory Design Pattern in C++ Ascending order in C++ How the value is passed in C++ Call by Pointer in C++ Constexpr in C++ Deadlock in C++ Design Patterns in C++ Factory Method for Designing Pattern in C++ How to calculate size of string in C++ Name Mangling and extern in C++ Preventing Object Copy in C++ Program that produces different results in C and C++ Quick Sort in C++ Single Handling in C++ Type difference of Character literals in C VS 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++ Isprint() in C++ List and Vector in C++ List iterators in C++ Merging Two Vectors in C++ Sleep function in C++ Stoi function in C++ String erase() in C++ String Trim in C++ When should we write own Assignment operator in C++ C++ tcp client server example C++ tcp server example 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++ 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++ Dynamic Casting in C++ 2D Vector Initialization in C++ C++ GUI Visual Studio C++ IPC C++ Macro Function Example C++ Permutation Overloading Stream Insertion in C++ Overloading array Index operator in C++ Operators that cannot be overloaded in C++ Operator overloading in C++ isprint() function in c++ Is_trivial function in C++ Is assignment operator Inherited in C++ div() function in C++ Default Assignment Operator and References in C++ Copy Constructor vs Assignment Operator in C++ Conversion Operator in C++ Array sum in C++ STL C++ Define Macro C++ Design C++ Factory Pattern TCP Client Server Example in C++ Convert String to Uppercase in C++ exit() and _Exit() in C and 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++ Set insert function in C++ Std partition_point in C++ Unary Operator Overloading in C++ Using Default Arguments with Virtual Functions Virtual Functions and Runtime Polymorphism What is endl in C++ What is Unary Operator Overloading in C++ Which operators cannot be overloaded in C++ C++ Program to Divide the String Into N equal Parts Gray Code to Binary Code in C++ How to get the value of pi in C++ Multimap value_comp() function in C++ Vector of Vectors in C++ Naïve Bayes Algorithm in C++ Minimum Cost Path Problem in C++ 10 C++ Programming Tricks You Should Know btowc() function in C++ forward_list::cend() in C++ Unordered_multimap max_load_factor() function in C++ Cpp_int in c++ Dynamic Objects in C++ FLOCK() FUNCTION IN C++ Generate Random Double Numbers in C++ How to Assign Infinity to a Number in C++ Jump statements in C++ Multipath inheritance in C++ Out of Range Exception in C++ Size of Class in C++ Size of string in C++ std::binary_negate in c++ Thread_local in C++ Tokenizing a String in C++ Ancestors of a Node in Binary Search Tree C++ program for Double to String Conversion C++ Program to Demonstrate Use of Formatting Flags on Float Output Clamp in C++ K-Dimensional Tree in C++ Mutable Lambda in C++ Power Set in C++ Program to Find Sum of Geometric Progression Std::Back_inserter in C++ Strpbrk() function in C++ Size of int in C++ TYPES OF MANIPULATORS IN C++ Double colon in C++ How to sort vector in C++ How to use Setprecision in C++ How to write a Vector in C++ Insertion in Splay Tree in C++ Merge Sort Algorithm in C++ Printing a Character using ASCII value in C++ Regex in C++ Size of Data Types in C++ Sqrtf() function in C++ Static Casting in C++ Using Range in Switch Case in C++ wcstoimax() and wcstoumax() function in C++ What is float in C++ What is the Diamond Problem in C++ Best way to learn C++ ios setstate() function in C++ Nested Namespace in C++ Single Inheritance in C++ std::fixed, std::scientific, std::hexfloat, std::defaultfloat in C++ StringStream in C++ for Decimal to Hexadecimal and back The OFFSETOF() macro in C++ Difference between std::next and std::advance in C++ Hiding of all overloaded methods with same name in base class in C++ C++ program to concatenate two strings using operator overloading Difference between array::fill() and array::swap() in C++ Difference between Friend Function and Virtual Function in C++ Semaphores in C++ Seekg in C++ UDP server- client implementattion in C++ What is long long in C++ CSV file management using C++ Toggle bits of a number except first and last bits in C++ Trailing Return Type C++ 11 Binary search implementation in C++ Different Versions of C++ What is Cascading in C++ Background Colour in C++ BOOL DATATYPE IN C++ BIT VECTORS IN C++ Literals in C++ Application of pointer in C++ Index with minimum sum of prefix and suffix sums in an array in C++ Maximum sum Bi-tonic sub-sequence in C++ std::optional in C++ C/C++ program for triangular matchstick number COUT COMMAND IN C++ LANGUAGE Adjacency matrix program in C++ language Difference between Null String and Empty String in C++ Character data type in c++ Constructors in Inheritance C++ Comma Operator Overloading in C++ Structure and Class in C++ Template Definition in C++ Tree Data Structure in C++ Typename in C++ C++ program to implement the bin packing algorithm How to merge multiple std::sets into a single std::set in C++? Stack Clear C++ C++ Friend Class Seekg in C++ Semaphores in C++ C++ Exceptions Difference Between C and C++ Double-linked list program in C++ Color Code in C++ CRC Program in C++ Anti-Clockwise spiral traversal of a binary tree in C++ Advantages of OOP in C++ Cryptarithmetic Puzzle in C++ Angular sweep algorithm in C++

Double colon in C++

With the help of the sophisticated programming language C++, developers have access to a variety of tools. A common element of C++ is the scope resolution operator, also referred to as the double colon (::). The double colon operators, despite being crucial to the language, can be confusing for many developers, especially those who are unfamiliar with it.

The double colon (::) operator in C++ will be discussed in this lesson, along with its numerous applications.

What is the C++ equivalent:: of its purpose?

The scope resolution operator/double colon (::) in C++ is used to get variable names at different scope levels. The scope of variables and functions in programming is used for the environment in which they can be accessed.

Uses of: in C++ in Various Situations

The scope resolution operator (::) has several uses in C++, based on the context. This operator is useful in the following situations:

  • Use a variable or function from a different namespace.
  • To minimize naming conflicts, C++ uses namespaces to organize related functions, classes, and variables. The name of a variable or function defined within a namespace is only accessible within that namespace.

1)Accessing a function in different namespace:

For accessing a variable or function defined by a separate namespace, make use of the scope resolution operator (::) together via the namespace name along with the variable or function name in C++. This enables us to access the variable or function inside a namespace other than the current one. This enables you to access the variable/function within a namespace apart from the one it was generated.

See the below code as an example to understand the previous case better:

Code:

#include <iostream>


using namespace std;


namespace math {


  const double PI = 3.14159;


  double square(double s) {


    return s * s;


  }


}


int main() {


  cout <<" Value of PI is " << math::PI << endl;


  cout << "Square of 7 is " << math::square(7) << endl;


  return 0;


}

Output:

Double colon in C++

The above code makes use of the math namespace for accessing the "PI" constant and "square" function through the scope resolution operator "::". It then outputs the values to the console.

2)Program Access to Global Variable

When two variables with the same name appear in the program, the local variable can cover up the global one. In such cases, the scope resolution operator (::) can be used to access the global variable. This operator helps us to make references to the global variable explicitly based on its scope.

For example, in the following code, we have used the scope resolution operator(::) to refer to the global variable 'a' from within a function that has a local variable having a similar name:

Code:

#include <iostream>


using namespace std;


int p = 23;


int main()


{


    int p = 57;


    cout << "Value of global variable p is " << ::p << endl;


    cout << "Value of local variable p is " << p << endl; // Corrected variable name


    return 0;


}

Output:

Double colon in C++

The variable p that exists on the outside of the main function is the global variable that is used in the example above. In contrast, the variable p existing inside the main function is a local variable having the same name as the global variable. The scope resolution operator was used in the cout statement to output the global variable p.

3)Create a Function Outside of the Class

Outside of the class definition, you may define a class function in C++ through the use of the scope resolution operator (::) to indicate which class the function belongs to. This is required since the function has been defined outside of the scope of the class.

Here's some code that explains how you can use the scope resolution operator:

Code:

#include <iostream>


using namespace std;


 class Class {


public:


  void Function();


};


void Class::Function() {


  cout << "Function() Called !";


}


int main()


{


  Class classobject;


  classobject.Function();


  return 0;


}

Output:

Double colon in C++

The scope resolution operator:: is used in the following code to denote that the member function Function() belongs to the Class class.

4)Static Class Members

When a class has a local variable with the same name as a static member, the static members will be found using the scope resolution operator (::). Now that the local variable and static member are distinct, the program can do so. This helps the program to tell the difference between a local variable and a static member. Here's some code that demonstrates how to utilize the scope resolution operator in this situation:

Code:

#include <iostream>


using namespace std;


class myClass {


public:


  static int myStatVar;


};


int myClass::myStatVar = 5;


int main() {


  // Removed the local variable with the same name


  cout << "Class variable myStatVar: " << myClass::myStatVar << endl;


  // Added a new value assignment to the static class variable


  myClass::myStatVar = 15;


  cout << "Updated Class variable myStatVar: " << myClass::myStatVar << endl;


  return 0;


}

Output:

Double colon in C++

Explanation:

  • To deal with input and output functions, we include the appropriate input/output library (#include iostream>).
  • We declare myClass, which contains a public static integer variable called myStatVar.
  • Within myClass, we use int myClass::myStatVar = 5; to set the static variable myStatVar to a value of 5. This signifies that all instances of myClass will share this variable.
  • We use cout to print the value of myClass::myStatVar in the main method directly. This displays the static variable's initial value, which is 5.
  • The static variable myClass::myStatVar is then set to 15 with myClass::myStatVar = 15;
  • Finally, we publish the static variable's updated value, 15, indicating that changes to a static variable affect all instances of the class.

5)With Multiple Inheritance

If a C++ class comes from multiple parent classes, the scope resolution operator (::) also serves to identify which version of a member to utilize. We can differentiate between different versions of similar members through the use of the scope resolution operator with the parent class name as well as the member's name.

Code:

#include <iostream>


using namespace std;


// Define the first parent class


class Parent1 {


public:


  void show() {


    cout << "This is class Parent1's show function." << endl;


  }


};


// Define the second parent class


class Parent2 {


public:


  void display() {


    cout << "This is class Parent2's display function." << endl;


  }


};


// Define a child class that inherits from both Parent1 and Parent2


class Child : public Parent1, public Parent2 {


private:


  int value1;


  int value2;


public:


  Child(int v1, int v2) {


    value1 = v1;


    value2 = v2;


  }


  void printValues() {


    Parent1::show();     // Call Parent1's show function


    Parent2::display();  // Call Parent2's display function


    cout << "Value 1: " << value1 << endl;


    cout << "Value 2: " << value2 << endl;


  }


};


int main() {


  Child obj(10, 20);   // Create an object of Child with values 10 and 20


  obj.printValues();    // Call the printValues() function of the object


  return 0;


}

Output:

Double colon in C++

Explanation:

  • There are two parent classes: Parent1 and Parent2. Each parent class has a unique function: show() in Parent1 and display() in Parent2.
  • Then, we define a child class called Child, which inherits from both Parent1 and Parent2. That is, it can use functions from both parent classes.
  • Within the Child class, we have two private variables, value1, and value2, which hold integer values. These serve as data containers for the child class.
  • When we construct a Child class object in the main() function with the values 10 and 20, we set value1 to 10 and value2 to 20.
  • There is also a printValues() function in the Child class. Within the scope of this function:
  • It invokes the show() function of Parent1 to display a message particular to Parent1.
  • It invokes the display() method of Parent2 to display a message particular to Parent2.
  • The values of values 1 and 2 are then printed to the screen.
  • We create an instance (object) of the Child class with the values 10 and 20 in the main() function and use its printValues() function to see all the messages and values printed out.

This code demonstrates how a child class can inherit and use functions from multiple parent classes, along with managing its data, making it a powerful feature in object-oriented programming.

Conclusion:

The scope resolution operator (::) is a crucial component in C++ that allows you to make use of variable names across various scope levels. The operator can be used to access variables or functions in a separate namespace, access a global variable, define a function inside the class, access static members of a class, and utilize multiple inheritances. Although it can be confusing for new developers, using the scope resolution operator (::) is fundamental for good programming practice.