PHP Call by Reference

Call by reference is all about passing the reference of the variable as a function parameter. Since PHP does not directly support the pointer kind of mechanism, it supports a reference to deal with various operations. In PHP language, the actual value of that holding variable will be modified if the value inside any function is modified; this can’t be achieved in the call by value. The ampersand (&) symbol can be used as a prefix while passing a variable as a reference in call be a reference. & symbol itself represents that a variable is being used as a reference. A reference function can also be passed as a parameter to another function. In this topic, we are going to learn about PHP Call by Reference.

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Syntax

There is no special syntax for using this, but yes, the & sign need to be used while passing a parameter to the function.

Function declaration could be like below:

function callByref(&$var)
{
$var.= 'inside the Call By Reference function.';
}

There is no need for any special thing while calling this function; the same can be used like a normal function (call by value).

$var = 'Yes, I am';
callByref ($var);

How does call by reference work in PHP?

Before moving ahead with the working of the call by reference, there should have been requirements so that can be fitted to a function. Then, in the declaration of that specified function, we can use the reference sign to a parameter variable. Let’s understand the same with a quick example.

function callByref(&$var)
{
$var.= 'Call By Reference function.';
}
$var = 'Try to check the reference, I am inside the ';

When we try to print the $var here, this will display the above message

echo $var;
// printing variable before calling function

Calling of the function now, calling this function will modify the actual value of the variable

$var as per written inside the function.

callByref ($var);
echo $var;
// this will be print the combined value of the string.

In the PHP language below mentioned can be used as a call by reference:

• Variable – a normal variable.
• A function that returns the reference – a well-defined function that returns the reference can also be passed as a function parameter in the call by reference (see the example E3).

Examples of the call by reference

Different examples are mentioned below:

Example #1

A simple program using the call by reference to check the nature of this function. In this, we can check the actual value is being modified after using the call by reference and modifying the variable from inside the function.

Code:

<?php
function callByref(&$var)
{
$var.= ' This will be added to the function.';
}
$var = 'Value before calling the function.';
echo $var ."<br><br>"; // printing variable before callig function
callByref ($var);
echo $var;
?>

Output:

Example #2

An example code is differentiating the call by value and call by reference in PHP.

Code

<?php
// call by value function
echo "<br>Swap functionality by call be value:<br>";
function SwapCallByValue($a, $b){
$c=$a;
$a=$b;
$b=$c;
echo "";
echo "<br>Value of a and b after swap: ";
echo $a . " ".$b;
}
$a = 10;
$b = 20;
echo "Value of a and b before swap: ";
echo $a . " ".$b;
SwapCallByValue($a, $b);
// swap functionality by call be a reference
echo "<br><br>Swap functionality by call by reference:<br>";
function SwapCallByRefernce(&$a,&$b)
{
$c=$a;
$a=$b;
$b=$c;
}
$a = 10;
$b = 20;
echo "Value of a and b before swap: ";
echo $a . " ".$b;
SwapCallByRefernce($a, $b);
echo "<br>Value of a and b after swap: ";
echo $a . " ".$b;
?>

Output:

As we can see in the above example, call-by-swap will not work if we print the value of a and the b outside of that function. This is because the call by value does not change the actual copy of the variable. But in the call by reference, we can see we are printing the value of a and b immediately after calling that function, and swapping works fine. This is all about while we will be dealing with the swapping functions with call by value and the call by reference.

Example #3

Code:

<?php
// this is the main function inside which the a funtion will be passed as a parameter
function mainFunction(&$val)
{
$val++;
echo $val;
}
// this function will be used as a parameter
function &FunctionAsAParam()
{
$val = 15;
return $val;
}
echo "A value of a after calling the function: ";
$result = mainFunction(FunctionAsAParam()); // calling function, function as a reference parameter
?>

Output:

In the above example, we can see that a reference function FunctionAsAParam() is used as another function parameter. As per the code written inside this, it assigns the value of the main variable. The function mainFunction() is the main function of the above code, is increasing the value of the value after using FunctionAsAParam() as a reference function parameter. There are various ways we can use the function as a reference parameter.

Conclusion

Call by reference uses the & symbol in the parameter at the time of creation, not at this function’s calling. In the C or the C++ language, it is usually used at the time of calling of this function, unlike PHP. The PHP call by reference is all about creating or calling a function that modifies the actual copy of the variable. Therefore, there is no reference sign is required at the time of calling at will gives the error in PHP.

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