Last Updated on March 28, 2023 by Prepbytes
In C, a global variable is one that is defined outside the scope of all functions. Because global variables have a global scope, they can be accessed and modified by any function, structure, or scope in C. Global variables are set before the main() function is called. They are not allowed to be defined within or after the main() function. Here we will discuss the global variable in c, the use of the global variable in c, advantages, and disadvantages of the global variable in c. You can also refer to a local and global variables in python.
What is the Global Variable in C
The Global Variable in c is usually declared just before the main function. To use memory efficiently, each programming language has different variables and their usage and syntaxes. A variable in a programming language is very useful. However, it is generally advised to avoid using global variables. Global variables can cause unaccounted problems in our programs because their values can be changed by any function.
Implementing singleton patterns and accessing registers in embedded systems are two examples of how global variables are used. Global variables can also be used to store constant values like pi in a program, or if a variable is used by multiple functions, we can declare it as global.
Example of a Global Variable in C in which we Declaring a Global Variable in C
A global variable can be declared by placing the variable outside of any function but within the scope of the entire program. For example, consider the following program:
Code Implementation
#include <stdio.h>
int num = 10;
void display();
int main()
{
printf("Value of num: %d\n", num);
display();
return 0;
}
void display()
{
printf("Value of num inside display function: %d\n", num);
}
Output
Value of num: 10
Value of num inside display function: 10Explanation
In the above program, the variable num is declared outside of any function, making it a global variable. The value of num is set to 10. The main() function prints the value of num, which is 10, and then calls the display() function. The display() function also prints the value of num, which is still 10.
The global variable num is accessible from both the main() function and the display() function, as it has been declared outside of any function. The main() function sets the value of num to 10 and prints it using printf(). The display() function also has access to the global variable num, so it can print the value of num using printf() as well.
Use of Global Variable in C
We now know that global variables are useful because we discussed their definition. At the very beginning of the program, we define a global variable. These variables retain their value throughout the program’s lifespan.
The global variables can be accessed by any block or function in the program. This means that once declared, we can use global variables as often as needed, and they are available for use throughout the program’s lifetime.
Advantages of a Global Variable in C
Here are the advantages of a global variable in c
- Accessibility: Global variables can be accessed from anywhere within a program, making them useful for sharing data between functions.
- Scope: Global variables have a scope that extends throughout the entire program. This means that they can be accessed from any function within the program, including functions that are called from other functions.
- Persistence: Global variables are initialized only once when the program starts and can retain their values throughout the lifetime of the program. This makes them useful for storing data that needs to be accessed by multiple functions over time.
- Simplification: Global variables can simplify programming by reducing the number of parameters that need to be passed between functions. So this makes code simple and clear to read and also reduces the amount of memory needed
- Initialization: Global variables can be initialized with a value when they are declared, which can make the code more efficient and reduce the number of lines of code needed to initialize the variable.
Disadvantages of a Global Variable in C
Here are the disadvantages of a global variable in c
- Security: Global variables can make it difficult to enforce data security because they are accessible from any part of the program, which makes it easier for malicious code to change sensitive data
- Readability and maintainability: Global variables can make it difficult to understand the code and its behavior because they can be modified by any part of the program.
- So we can say global variables make code harder to debug especially when multiple developers are working.
- Dependency: Global variables can create dependencies between different parts of the program, which can make it harder to make changes to the code. This can result in bugs, errors, and other problems that can be difficult to identify and fix.
- Scalability: Global variables can make it difficult to scale a program as it grows in complexity or size. This is because global variables can introduce unexpected interactions between different parts of the program, which can result in performance issues, memory leaks, or other problems.
- Testing: Global variables can make it harder to test a program because they can introduce unpredictable behavior that is difficult to control.
Conclusion
Global variable in c is an important concept in C programming, allowing data to be shared between functions and persist throughout the lifetime of a program. By using global variables wisely, programmers can simplify their code and make it easier to maintain and understand. Global variables can be accessed from anywhere within a program, making them useful for sharing data between functions. Global variables can be used to store data that needs to persist throughout the lifetime of a program. Global variables can lead to unintended consequences when multiple functions try to modify the same global variable at the same time. Global variables can make it difficult to understand the flow of a program, as it may not always be clear which functions are modifying the global variable.
Frequently Asked Questions(FAQ)
Here are the FAQs on the global variable in c
Q1. Can two global variables in different files have the same name?
Ans. Yes, two global variables in different files can have the same name without causing any conflicts. This is because each global variable has a unique scope that extends throughout the entire program, so the variables are separate and can be accessed independently.
Q2. What is the lifetime of a global variable in C?
Ans. The lifetime of a global variable in C is the entire lifetime of the program. Global variables are initialized before the program starts and remain in memory until the program terminates.
Q3. How do you avoid using global variables in C?
Ans. To avoid using global variables in C, you can use local variables instead or pass data between functions using parameters. You can also use other programming constructs like structs, arrays, and pointers to share data between functions in a more controlled and modular way.
Q4. Can a global variable be declared as const in C?
Ans. Yes, a global variable can be declared as const in C. Declaring a global variable as const means that its value cannot be modified throughout the program, providing an additional level of security and preventing accidental modification of the variable.