Local vs Global Variables: Difference and Comparison

Since computers have become a huge aspect of our lives now and, as we all are aware of, have enslaved us, it never hurts to know a few of the details that help us on a day-to-day basis.

To delve into a topic that is quite technical and deep, we should take a look at the concept of variables and the difference between their types- local and global.

Key Takeaways

1. Local variables exist within a specific function, limiting their scope and accessibility to that function alone.
2. Global variables are accessible throughout the program, allowing data sharing among multiple functions.
3. The use of local variables can enhance code readability and maintainability, while global variables should be used sparingly to avoid potential conflicts.

Local vs Global Variables

A local variable is defined within a function and can only be accessed within that function. It disappears after the function is executed. A global variable is defined outside of any function and can be accessed by any function in the program

A local variable happens to be a kind of variable. It is declared inside the function, and its lifetime ranges from its execution to its termination.

Its scope is also limited within the function in which it has been declared. It can store the “garbage value” if it is uninitialized.

On the other hand, a global variable is also a type of variable. It is characterized by being declared outside the function.

It is created even before the program’s execution begins; however, it ends with the termination of the program. If it is uninitialized, then it stores zero as default.

Comparison Table

Parameters of Comparison	Local Variables	Global Variables
Data Sharing	This is impossible here, as only one function can access the data.	As multiple functions can access it, this feature is possible
Parameter	The passing of parameters to access value is of utmost necessity	The passing of parameters is not of utmost necessity as the value can be accessed throughout the program.
Modifications	If the value is modified in one of the functions, then such modifications do not reflect in the other functions.	If the value is modified in one of the functions, t.hen such modifications reflect throughout the program
Accessibility	This can be accessed through the statements contained inside a function.	This can be accessed through any statement that is there in the program.
Storage	This is stored in an unspecified location unless specified.	This is stored in a specified location.

What are Local Variables?

This is a kind of variable. Its features are that it is declared within or inside a certain function, and the value of it can only be accessed by such a statement that has been incorporated into the function.

Its shelf-life commences when the execution of the program begins and ends with its termination of it.

Another aspect is that its scope is also limited within the function in which it has been declared. It can store the “garbage value” if it is uninitialized.

For this, data sharing isn’t possible, and this is because the data can only be accessed by one function. Also, the passing of parameters to access value is of utmost necessity.

Another factor that is to be noted is that if the value is modified in one of the functions, then such modifications do not reflect in the other functions.

This can be accessed through the statements contained inside a function.

It has a few advantages, such as guaranteeing that the values will be intact even when the task is running. As each task creates its local variable, the results will still be predictable.

They are deleted with the completion of any function, thereby releasing the previously occupied memory space.

What are Global Variables?

This, too, is a kind of variable. It is characterized by being declared outside the function. It is created even before the program’s execution begins; however, it ends with the termination of the program.

If it is uninitialized, then it stores zero as default. Data-sharing is possible here because multiple functions can access it. This feature is possible.

The passing of parameters is not of utmost necessity as the value can be accessed all through by virtue of the variables being declared outside the functions.

If the value is modified in one of the functions, then such modifications reflect throughout the program. This can be accessed through any statement that is there in the program.

It has certain advantages, such as it can be accessed from all the functions of the program. It is pivotal in storing “constants” and aids in maintaining consistency.

This is most useful when multiple functions access the same data. Its downsides are that several variables remain in the memory until the execution of the program, which in turn can lead to the “Out of Memory” problem.

Furthermore, sometimes the results can be unreliable and unpredictable as any function can change or alter the data.

Main Differences Between Local and Global Variables

1. While Local Variables have acquired their name based on how they perform, that is, they are inside functions, Global Variables, too, have acquired their name from the fact that they are outside functions.
2. The life of the variable for Local Variables commences with the execution of the program and ends with its termination of it. In contrast, the life of the variable in Global Variable commences even before the execution of the program. However, it ends with its termination.
3. Local variables have their storage in unspecified stacks if they aren’t specified. On the other hand, Global variables’ storage is at a fixed location.
4. Where the results produced in Local Variables have no scope for alteration, the results can be unreliable and unpredictable as the data can be changed or altered by any function in the case of Global Variables.
5. While data-sharing cannot be possible in the case of Local Variables, it is just the opposite in the case of Global Variables.

References

1. https://onlinelibrary.wiley.com/doi/full/10.1111/cogs.12831
2. https://www.sciencedirect.com/science/article/pii/S1878029615001905

Last Updated : 11 June, 2023