Learn PHP

function parameter

PHP functions can optionally accept one or more arguments, which are values passed to the function.

A parameter is a variable that holds the value passed to it when the function is called.


To specify parameters for your function, insert one or more variable names between the parentheses

	      	function myFunc( $oneParameter, $anotherParameter,... ) { 
			  // (do stuff here) 

Example - Add parameter to a function

We need to give each parameter a name to refer to it inside the function. PHP will copy the values it receives into these parameters:

			function multiply($num1, $num2) { 
			        $total = $num1 * $num2; 
			        print $num1;
			        print "\n";
			        print $num2;
			        return $total; 
			$mynum = multiply(5, 10); 
			echo $mynum;


		  	<!DOCTYPE html>
			    <h2>A function to create a definition list
			    $iterations = 10;
			    function defList( $contents ) {
			      $markup = "<dl>\n";
			      foreach ( $contents as $key => $value ) {
			        $markup .= "  <dt>$key</dt><dd>$value</dd>\n";
			      $markup .= "</dl>\n";
			      return $markup;
			    $myBook = array( "title" => "The Grapes of Wrath",
			                     "author" => "John Steinbeck",
			                     "pubYear" => 1939 );
			    echo defList( $myBook );


PHP Function Default Parameters

Default parameter can have a value if the corresponding argument is not passed when the function is called.

PHP lets you create functions with optional parameters. You define an optional parameter as follows:

		  	function myFunc( $parameterName=defaultValue ) { 
			  // (do stuff here) 

To define default parameters for a function, add the default value after the variables.


Example - optional arguments

			function calcSalesTax($price, $tax="") 
			    $total = $price + ($price * $tax);
			    echo "Total cost: $total";


PHP Variable Length Parameter

A function with variable-length parameter list can take as many parameters as user want.

We can use three functions to make a function handle variable length parameters.

  • func_num_args()
  • func_get_arg(), and
  • func_get_args()

func_num_args() and func_get_args() take no parameters.

  • func_num_args() gets the number of arguments passed into your function.
  • func_get_arg() gets the value of an individual parameter.
  • func_get_args() returns an array of the parameters that were passed in.

			function some_func($a, $b) { 
			        for ($i = 0; $i < func_num_args(); ++$i) { 
			                $param = func_get_arg($i); 
			                echo "Received parameter $param.\n"; 

			function some_other_func($a, $b) { 
			        $param = func_get_args(); 
			        $param = join(", ", $param); 
			        echo "Received parameters: $param.\n"; 


Example - variable number of argument

			  function makeList()
			    for($i=0; $i < func_num_args(); $i++)
			      print("<li>" . func_get_arg($i) . "</li>\n");

			  makeList("Linux", "HTML", "MySQL", "PHP");

PHP Function Reference Parameter

A reference is a pointer to a PHP variable.

Syntax to create reference variable

$myRef = &$myVariable;

Reference variable

We have two ways to read or change the variable's contents. We can use the variable name, or you can use the reference.

	         $myVar = 123; 
	         $myRef = &$myVar; 
	         echo $myRef . "\n";  // Displays "124" 
	         echo $myVar . "\n";  // Displays "124"   

Note the ampersand (&) symbol after the equals sign; using this symbol creates the reference.

Syntax for reference parameters

To get a function to accept an argument as a reference rather than a value, put an ampersand (&) before the parameter name within the function definition:

		  	function myFunc(  & $aReference ){ 
			  // (do stuff with $aReference) 

By passing a reference to a variable as an argument to a function, rather than the variable itself, you pass the argument by reference , rather than by value.

This means that the function can now alter the original value, rather than working on a copy.

			    function resetCounter(  & $c ) { 
			      $c = 0; 

			    $counter = 0; 
			    echo "$counter\n";  // Displays "3" 
			    resetCounter( $counter ); 
			    echo "$counter\n";  // Displays "0"   

			    $cost = 20.99;
			    $tax = 0.0575;

			    function calculateCost(&$cost, $tax)
			        // Modify the $cost variable
			        $cost = $cost + ($cost * $tax);

			        // Perform some random change to the $tax variable.
			        $tax += 4;
			    calculateCost($cost, $tax);
			    printf("Tax is %01.2f%% ", $tax*100);
			    printf("Cost is: $%01.2f", $cost);

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