What are the functions in php?

The real power of PHP comes from its functions.

PHP has more than 1000 built-in functions, and in addition you can create your own custom functions.

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.

Please check out our PHP reference for a complete overview of the PHP built-in functions.

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 User Defined Function in PHP

A user-defined function declaration starts with the word function:

Syntax

function functionName() {
  code to be executed;
}

Note: A function name must start with a letter or an underscore. Function names are NOT case-sensitive.

Tip: Give the function a name that reflects what the function does!

In the example below, we create a function named "writeMsg()". The opening curly brace ( { ) indicates the beginning of the function code, and the closing curly brace ( } ) indicates the end of the function. The function outputs "Hello world!". To call the function, just write its name followed by brackets ():

Example

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

writeMsg(); // call the function
?>

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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.

The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:

Example

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

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

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The following example has a function with two arguments ($fname and $year):

Example

function familyName($fname, $year) {
  echo "$fname Refsnes. Born in $year
";
}

familyName("Hege", "1975");
familyName("Stale", "1978");
familyName("Kai Jim", "1983");
?>

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PHP is a Loosely Typed Language

In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.

In PHP 7, type declarations were added. This gives us an option to specify the expected data type when declaring a function, and by adding the strict declaration, it will throw a "Fatal Error" if the data type mismatches.

In the following example we try to send both a number and a string to the function without using strict:

Example

function addNumbers(int $a, int $b) {
  return $a + $b;
}
echo addNumbers(5, "5 days");
// since strict is NOT enabled "5 days" is changed to int(5), and it will return 10
?>

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To specify strict we need to set declare(strict_types=1);. This must be on the very first line of the PHP file.

In the following example we try to send both a number and a string to the function, but here we have added the strict declaration:

Example

function addNumbers(int $a, int $b) {
  return $a + $b;
}
echo addNumbers(5, "5 days");
// since strict is enabled and "5 days" is not an integer, an error will be thrown
?>

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The strict declaration forces things to be used in the intended way.

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

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

setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
?>

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PHP Functions - Returning values

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

Example

function sum(int $x, int $y) {
  $z = $x + $y;
  return $z;
}

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

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PHP Return Type Declarations

PHP 7 also supports Type Declarations for the return statement. Like with the type declaration for function arguments, by enabling the strict requirement, it will throw a "Fatal Error" on a type mismatch.

To declare a type for the function return, add a colon ( : ) and the type right before the opening curly ( { )bracket when declaring the function.

In the following example we specify the return type for the function:

Example

function addNumbers(float $a, float $b) : float {
  return $a + $b;
}
echo addNumbers(1.2, 5.2);
?>

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You can specify a different return type, than the argument types, but make sure the return is the correct type:

Example

function addNumbers(float $a, float $b) : int {
  return (int)($a + $b);
}
echo addNumbers(1.2, 5.2);
?>

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Passing Arguments by Reference

In PHP, arguments are usually passed by value, which means that a copy of the value is used in the function and the variable that was passed into the function cannot be changed.

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:

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

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

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PHP Exercises

What are the types of functions in PHP?

How many types of functions are there in PHP?

What is the function name in PHP?

WHAT IS function and method in PHP?