Do you think IIT Guwahati certified course can help you in your career?
Introduction
In PHP, functions can pass arguments using Call by Value or Call by Reference. In Call by Value, a copy of the variable is passed, so changes inside the function do not affect the original variable. In Call by Reference, the actual variable is passed using the & symbol, allowing the function to modify its value.
In this article, you will learn the differences between Call by Value and Call by Reference in PHP with examples to understand their usage.
Call By Value
Call by value is the default way of passing arguments to a function in PHP. When a variable is passed using call by value, a copy of the variable’s value is sent to the function. This means that any changes made to the variable inside the function do not affect the original variable.
Example of Call By Value
<?php
function increaseValue($num) {
$num += 10; // Increase the value by 10
echo "Value inside function: $num\n";
}
$originalValue = 20;
increaseValue($originalValue);
echo "Original value after function call: $originalValue\n";
?>
You can also try this code with Online PHP Compiler
Value inside function: 30
Original value after function call: 20
Explanation:
The function increaseValue takes a parameter $num.
The value of $num is increased by 10 inside the function.
However, the original variable $originalValue remains unchanged because only a copy was modified inside the function.
Call by Reference
In call by reference, instead of passing a copy of the variable, the actual memory address of the variable is passed. This means that any changes made inside the function directly affect the original variable.
To pass a variable by reference, we use the ampersand (&) before the parameter name in the function definition.
Example of Call By Reference
<?php
function increaseValueByReference(&$num) {
$num += 10; // Increase the value by 10
echo "Value inside function: $num\n";
}
$originalValue = 20;
increaseValueByReference($originalValue);
echo "Original value after function call: $originalValue\n";
?>
You can also try this code with Online PHP Compiler
Value inside function: 30
Original value after function call: 30
Explanation:
The function increaseValueByReference takes a parameter by reference using &$num.
The value of $num is increased by 10 inside the function.
Since the variable is passed by reference, changes made inside the function affect the original variable $originalValue.
When to Use Call by Value and Call by Reference in PHP?
Choosing between call by value & call by reference depends on the specific requirements of your program. Let’s discuss when to use each method:
When to Use Call by Value
Call by value is the default behavior in PHP, & it’s ideal in the following situations:
1. Preserving Original Data: If you want to ensure that the original data remains unchanged, use call by value. This is useful when you’re working with sensitive or critical data that should not be modified accidentally.
2. Working with Simple Data Types: For simple data types like integers, floats, or strings, call by value is often sufficient. Since these data types are small in size, creating a copy doesn’t significantly impact performance.
3. Avoiding Side Effects: Call by value prevents unintended side effects because changes inside the function don’t affect the original variable. This makes your code more predictable & easier to debug.
When to Use Call by Reference
Call by reference is useful in specific scenarios where you need to modify the original data directly. Let’s take a look at a few common use cases:
1. Modifying Original Data: If your function needs to update the original variable, use call by reference. This is common in functions that perform operations like sorting, filtering, or updating values.
2. Working with Large Data Structures: For large data structures like arrays or objects, call by reference can improve performance. Instead of creating a copy of the entire data structure, PHP works directly with the original, saving memory & processing time.
3. Returning Multiple Values:PHPfunctions can only return one value directly. If you need to return multiple values, you can use call by reference to modify multiple variables passed to the function.
Differences Between Call By Value and Call By Reference
Parameters
Call By Value
Call By Reference
Passing Method
Passes a copy of the variable
Passes the actual variable reference
Effect on Original Variable
No change
Changes reflect in the original variable
Memory Usage
Uses more memory (creates a copy)
Uses less memory (no duplication)
Performance
Slower for large data structures
Faster for large data structures
Use Case
When data should not be modified
When changes should persist outside the function
Frequently Asked Questions
When should I use call by value in PHP?
Use call by value when you do not want the original variable to be modified by the function.
What is the advantage of using call by reference?
Call by reference saves memory and allows functions to modify variables directly, making it useful for handling large datasets.
How can I prevent a function from modifying my original variable?
Use call by value (default method) to ensure that a function receives a copy of the variable, keeping the original data intact.
Conclusion
In this article, we explored Call by Value and Call by Reference in PHP and how they affect function arguments. Call by Value passes a copy of the variable, keeping the original unchanged, while Call by Reference passes the actual variable, allowing modifications. Understanding these concepts helps in writing efficient and optimized PHP code with better memory management.
34+ registered 
