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Call By Value in C++

In this article, you will learn about the call by value in C++ with its mechanism, examples, advantages, and disadvantages.

Introduction to Call by Value

Passing the data to functions or methods is a common thing while programming. It allows you to modularize your code, reuse functionality, and make it more organized. Call by value is one of the mechanisms used for passing data in C++, and it is essential to understand how it works and its implications.

In call by value, a copy of the passed data is created, which is what the function or method operates on. It means that any changes made to the data within the function do not affect the original data outside the function's scope. While it might sound counterintuitive initially, it has its own advantages and limitations that significantly impact program behavior.

Mechanism of Call by Value

The process of call by value involves creating a duplicate of the passed data. It ensures that any modifications made to the data within the function do not alter the original data. When a function is called with arguments passed by value, the values of these arguments are copied into the function's parameter variables. After that, this copy is used within the function's scope, leaving the original data unchanged. This behavior is particularly useful when you want to ensure the immutability of the original data.


Let's take a program to illustrate the call by value and call by reference in C++.


Call By Value in C++


In this example, a local variable sum is passed by value in function1. The function iterates through a loop ten times, adding the loop index to the sum in each iteration. However, as the sum is passed by value, the modifications to it within the function are confined to the function's scope, and the original variable remains unaffected. In the main function, the original variable retains its initial value even after calling function1.

In contrast, function2 takes an integer reference sum as an argument. It means any modifications to the sum inside the function directly affect the original variable in the main function. In function2, the loop increments the sum by the loop index, effectively modifying the original variable. Consequently, when function2 is called in the main function, the original variable's value is altered accordingly.

Finally, in the main function, an initial value of num is set to zero. After calling function1, the value of num remains unchanged, demonstrating that passing by value doesn't modify the original variable. However, after calling function2, the value of num changes because it's being passed by reference, allowing modifications within the function to directly affect the original variable.

Advantages of Call by Value:

Call by value has several advantages that make it a valuable tool in C++ programming:

  • Predictable Behavior:

As the function works on a copy of the data, the original data remains unchanged, providing a clear and predictable outcome.

  • Immutability of Original Data:

Call by value offers a convenient solution in scenarios where you want to ensure that the function does not alter the original data.

  • Enhanced Memory Management:

Call by value reduces the risk of memory leaks and unintended changes, as the function operates on isolated copies of data.

Limitations of Call by Value

There are several limitations of the call by value in C++. Some main limitations of call by value are as follows:

  • Performance Overhead:

Creating a copy of data can be resource-intensive, especially for large objects. It can impact the program's performance.

  • Inefficiency with Large Data:

For objects with significant memory footprints, passing them by value can lead to unnecessary memory consumption and slow execution.

  • Limited Impact on Original Data:

As the function operates on a copy, any changes made within the function do not affect the original data. It might not be suitable for all scenarios.

Comparing Call by Value and Call by Reference

Call by value is just one of the mechanisms for passing data in C++. Another common approach is call by reference. In call by reference, a reference to the original data is passed to the function, allowing the function to directly modify the original data.

Comparing the two approaches involves considering factors such as the desired behavior, efficiency, and data mutability. Call by value is preferable when you want to maintain the integrity of the original data and avoid unintended modifications. On the other hand, call by reference is useful when you want to directly manipulate the original data within the function.

Uses of Call by Value:

Let's explore some real-world scenarios where call by value is used in C++.

Programming: Passing Basic Data Types by Value:

Call by value is commonly used for passing basic data types like integers, floats, and characters. It ensures that the original values are not altered by the function's operations.

  • Passing Objects by Value:

Objects of user-defined classes can be passed by value to functions. It is especially useful when you want to work with a local copy of the object without modifying the original.

  • Copy-on-Write Optimization:

Some data structures and implementations use copy-on-write optimization. It means that a copy is only made when modifications are attempted, optimizing memory usage. Strings in C++ are often implemented with this optimization.

Best Practices of Call by Value:

Consider the following best practices to make the most of call by value:

  • Use Call by Value for Immutability:

Call by value is a suitable choice when you want to ensure that the original data remains unchanged.

  • Optimize Performance with Constants:

For large objects, consider passing them by constant reference (const reference) to avoid the performance overhead of copying.

  • Avoid Unnecessary Copies:

Be secure of unnecessary copies. If you only need to read the data within the function, consider using constant references instead of call by value.


Understanding call by value is a cornerstone of effective C++ programming. It governs how data is passed to functions and methods, influencing memory management, program behavior, and code efficiency. By grasping the mechanism, advantages, limitations, and real-world applications of call by value, programmers can make informed decisions about when and how to use this approach in their projects. Balancing the benefits of immutability and predictability with the performance considerations associated with copying data is essential for creating robust and optimized C++ programs.

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