Passed by value and passed by reference in php

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What is Pass By Reference and Pass By Value in PHP?

In this article, we will learn about pass by value and pass by reference in PHP.

Now, let’s understand these two concepts in detail.

In PHP generally, we followed to pass the arguments to the function with passed by value approach. We are following this practice because if the value of the argument within the function is changed, it does not get changed outside of the function.

In some cases we may need to modify function arguments, So to allow a function to modify its arguments, they must be passed by reference.

Let’s begin with passed by reference. As it is already mentioned we can pass a variable by reference to a function so the function can modify the variable. To begin the process of passing the parameters passed by reference, prepend an ampersand (&) to the argument name in the function definition.

Example

Let’s test this with a simple example.

Output

Explanation

Here we have declared variable $a and passing it as pass by reference to the function calculate(). So as the principle says if the value of the $a gets changed inside the function then it will be also going to change outside the function.

Note

There is no reference sign on a function call — only on function definitions. Function definitions alone are enough to correctly pass the argument by reference. This is deprecated in 5.4 version of PHP when you use to calculate(&$a); it throws an error.

Example

Let’s test an example to understand pass by value.

Output

Explanation

Here we have passed the value to the function calculate() as pass by value. Its value gets changed inside the function but that is not reflected outside the function. The value of the variable remains the same outside the function.

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PHP Passing by Reference

In PHP, arguments to a function can be passed by value or passed by reference. By default, values of actual arguments are passed by value to formal arguments which become local variables inside the function. Hence, modification to these variables doesn’t change value of actual argument variable.

When arguments are passed by reference, change in value of formal argument is reflected in actual argument variable because the former is a reference to latter. Thus pass by reference mechanism helps in indirectly manipulating data in global space. It also helps in overcoming the fact that a function can return only one variable.

Pass by Value

In following example, two variables are passed to swap() function. Even though swapping mechanism takes place inside the function it doesn’t change values of variables that were passed

Example

"; $temp=$arg1; $arg1=$arg2; $arg2=$temp; echo "inside function after swapping: arg1=$arg1 arg2=$arg2
"; > $arg1=10; $arg2=20; echo "before calling function : arg1=$arg1 arg2=$arg2
"; swap($arg1, $arg2); echo "after calling function : arg1=$arg1 arg2=$arg2
"; ?>

Output

This example gives following output

before calling function : arg1=10 arg2=20 inside function before swapping: arg1=10 arg2=20 inside function after swapping: arg1=20 arg2=10 after calling function : arg1=10 arg2=20

Pass by reference

In order to receive arguments by reference, variable used formal argument must be prefixed by & symbol. It makes reference to variables used for calling the function. Hence, result of swapping inside function will also be reflected in original variables that were passed

Example

"; $temp=$arg1; $arg1=$arg2; $arg2=$temp; echo "inside function after swapping: arg1=$arg1 arg2=$arg2
"; > $arg1=10; $arg2=20; echo "before calling function : arg1=$arg1 arg2=$arg2
"; swap($arg1, $arg2); echo "after calling function : arg1=$arg1 arg2=$arg2
"; ?>

Output

Result of swapping will be shown as follows

before calling function : arg1=10 arg2=20 inside function before swapping: arg1=10 arg2=20 inside function after swapping: arg1=20 arg2=10 after calling function : arg1=20 arg2=10

In following example, array element are references to individual variables declared before array initialization. If element is modified, value of variable also changes

Example

Output

Values of $a, $b and $c also get incremented

It is also possible to pass by reference an array to a function

Example

 $arr=[1,2,3,4,5]; arrfunction($arr); foreach ($arr as $i) echo $i . " "; ?>

Output

Modified array will be displayed as follows

Object and reference

In PHP, objects are passed by references by default. When a reference of object is created, its reference is also sent as argument in the form of $this which is also reference to first object

Example

name; > function setname($name)< $this->name=$name; > > $obj1=new test1(); $obj2=&$obj1; $obj1->setname("Amar"); echo "name: " .$obj2->getname(); ?>

Output

Above code will display following output

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