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

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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 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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 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C++ Global Variable
2023-02-27 01:39:12

C++ Global Variable

In C++, a global variable is a variable that is defined outside of any function or class and can be accessed by any function or class in the program. Global variables are typically defined at the top of a source file before any functions or classes are defined. They are often used to store data that needs to be shared across multiple functions or classes. However, the use of global variables can lead to code that is difficult to maintain and debug, as it can be unclear where a particular variable is being modified. Additionally, global variables can also lead to naming conflicts if two or more variables have the same name.

C++ Global Variable

Use of Global Variable

The use of global variables can lead to a number of problems, However, one of the main issues with global variables is that they can make code difficult to maintain and debug. Because global variables can be accessed and modified from anywhere in the program, it can be unclear where a particular variable is being modified, and this can make it difficult to track down bugs. Additionally, global variables can also lead to naming conflicts if two or more variables have the same name.

Another issue with global variables is that they can introduce tight coupling between different parts of the program. When a global variable is used in multiple functions or classes, changes to the value of that variable can have unintended consequences in other parts of the program. This can make it difficult to make changes to the program without breaking other parts of the code.

In general, it is considered best practice to minimize the use of global variables and to use them only when necessary. Instead of using global variables, it is often better to pass data as function arguments or to use class variables and methods to encapsulate data and behavior. Additionally, it can also be useful to use the "const" keyword to define read-only global variables, to prevent the value of the variable from being accidentally modified.

In conclusion, while global variables can be useful in certain situations, they should be used with caution. The use of global variables can lead to code that is difficult to maintain and debug and can introduce tight coupling between different parts of the program. It is generally considered best practice to minimize the use of global variables, and to use them only when necessary. Instead of using global variables, it is often better to pass data as function arguments or to use class variables and methods to encapsulate data and behavior.

Example of C++ global variable

Here is an example of a global variable in C++:

#include <iostream>


// Global variable
int g_counter = 0; // Initial value is 0


void incrementCounter()
{
    g_counter++;
}


int main()
{
    std::cout << "Counter: " << g_counter << std::endl; // Outputs "Counter: 0"
    incrementCounter();
    std::cout << "Counter: " << g_counter << std::endl; // Outputs "Counter: 1"
    return 0;
}

Output:

Counter: 0
Counter: 1

In this example, the variable "g_counter" is a global variable that is defined at the top of the file, before any functions or classes. The variable is assigned an initial value of 0. The function "incrementCounter" increments the value of the global variable by 1. The main function then prints the value of the global variable to the console. As the global variable is accessible to all functions, the main function can access and modify the value of the global variable.

Also, it is important to note that the use of global variables may lead to naming conflicts, and tight coupling between different parts of the program and can make code difficult to maintain and debug.

Scope of C++ Global Variable

The scope of a global variable in C++ is the entire program. This means that a global variable can be accessed and modified from any function or class in the program, regardless of where it is defined. Global variables are typically defined at the top of a source file before any functions or classes are defined, but they can also be defined in a header file and included in multiple source files.

It is worth noting that global variables are also global to all compilation units (i.e files) if they are defined in the header files, so it is important to be mindful of the scope in which global variables are defined. If a global variable is defined in a header file and included in multiple source files, it will be accessible from all of those source files, creating a global variable that can be accessed and modified from multiple compilation units.

It is also worth noting that global variables can also be accessed and modified by other source files that are linked to the program. This means that if a global variable is defined in one source file and then another source file is linked to the program that also defines a global variable with the same name, the two variables will refer to the same memory location.