PHP Functions

PHP functions are reusable blocks of code that perform specific tasks. They are essential for organizing your code, improving readability, and promoting modularity in your PHP applications.

• PHP Built-in Functions

PHP has over 1000 built-in functions that can be called directly, from within a script, to perform a specific task.

• PHP User Defined Functions

Besides the built-in PHP functions, it is possible to create your own functions.

A function is a block of statements that can be used repeatedly in a program.
A function will not execute automatically when a page loads.
A function will be executed by a call to the function.

• Create a Function

A user-defined function declaration starts with the keyword function, followed by the name of the function:

Example

function myMessage() {
echo "Hello world!";
}

• Call a Function

To call the function, just write its name followed by parentheses ():

Example

<!DOCTYPE html>
<html>
<body>

<?php
function myMessage() {
  echo "Hello world!";
}

myMessage();
?> 

</body>
</html>

Output

Hello world!

• PHP Function Arguments

Information can be passed to functions through arguments. An argument is just like a variable.

Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.

Example

<!DOCTYPE html>
<html>
<body>

<?php
function familyName($fname) {
  echo "$fname Refsnes.
";
}

familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
?>

</body>
</html>

Output

Jani Refsnes.
Hege Refsnes.
Stale Refsnes.
Kai Jim Refsnes.
Borge Refsnes.

• PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

Example

<!DOCTYPE html>
<html>]==['
l36.t;body>

<?php
function setHeight($minheight = 50) {
  echo "The height is : $minheight 
";
}

setHeight(350);
setHeight();
setHeight(135);
setHeight(80);
?>

</body>
</html>

Output

The height is : 350
The height is : 50
The height is : 135
The height is : 80

• PHP Functions - Returning values

To let a function return a value, use the return statement:

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Example

<!DOCTYPE html>
<html>
<body>

<?php
function sum($x, $y) {
  $z = $x + $y;
  return $z;
}

echo "5 + 10 = " . sum(5,10) . "
";
echo "7 + 13 = " . sum(7,13) . "
";
echo "2 + 4 = " . sum(2,4);
?>

</body>
</html>

Output

5 + 10 = 15
7 + 13 = 20
2 + 4 = 6

• Passing Arguments by Reference

When a function argument is passed by reference, changes to the argument also change the variable that was passed in. To turn a function argument into a reference, the & operator is used

Example

Use a pass-by-reference argument to update a variable:

<!DOCTYPE html>
<html>
<body>

<?php
function add_five(&$value) {
  $value += 5;
}

$num = 2;
add_five($num);
echo $num;
?>

</body>
</html>

Output

• Variable Number of Arguments

By using the ... operator in front of the function parameter, the function accepts an unknown number of arguments. This is also called a variadic function.

The variadic function argument becomes an array.

Example

A function that do not know how many arguments it will get:

<!DOCTYPE html>
<html>
<body>

<?php
function sumMyNumbers(...$x) {
  $n = 0;
  $len = count($x);
  for($i = 0; $i < $len; $i++) {
    $n += $x[$i];
  }
  return $n;
}

$a = sumMyNumbers(5, 2, 6, 2, 7, 7);
echo $a;
?>

</body>
</html>