PHP Functions
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 Function
A user-defined function declaration starts with the keyword function
,
followed by the name of the function:
Example
function myMessage() {
echo "Hello world!";
}
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!
Call a Function
To call the function, just write its name followed by parentheses
()
:
In our example, we create a function named myMessage()
.
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!".
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 "$fname Refsnes.<br>";
}
familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
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The following example has a function with two arguments ($fname, $year)
:
Example
function familyName($fname, $year) {
echo "$fname Refsnes. Born in $year <br>";
}
familyName("Hege", "1975");
familyName("Stale", "1978");
familyName("Kai Jim", "1983");
Try it Yourself »
PHP Default Argument Value
The following example shows how to use a default parameter. If we call the
function setHeight()
without arguments it takes the default value as argument:
Example
function setHeight($minheight = 50) {
echo "The height is : $minheight <br>";
}
setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
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PHP Functions - Returning values
To let a function return a value, use the return
statement:
Example
function sum($x, $y) {
$z = $x + $y;
return $z;
}
echo "5 + 10 = " . sum(5, 10) . "<br>";
echo "7 + 13 = " . sum(7, 13) . "<br>";
echo "2 + 4 = " . sum(2, 4);
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Passing Arguments by Reference
In PHP, arguments are usually passed by value, which means that a copy of the value is used in the function and the variable that was passed into the function cannot be changed.
When a function argument is passed by reference, changes to the argument also change
the variable that was passed in. To turn a function argument into a reference, the &
operator is used:
Example
Use a pass-by-reference argument to update a variable:
function add_five(&$value) {
$value += 5;
}
$num = 2;
add_five($num);
echo $num;
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Variable Number of Arguments
By using the ...
operator in front of the function parameter, the function
accepts an unknown number of arguments. This is also called a variadic function.
The variadic function argument becomes an array.
Example
A function that do not know how many arguments it will get:
function sumMyNumbers(...$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 $a;
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You can only have one argument with variable length, and it has to be the last argument.
Example
The variadic argument must be the last argument:
function myFamily($lastname, ...$firstname) {
txt = "";
$len = count($firstname);
for($i = 0; $i < $len; $i++) {
$txt = $txt."Hi, $firstname[$i] $lastname.<br>";
}
return $txt;
}
$a = myFamily("Doe", "Jane", "John", "Joey");
echo $a;
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If the variadic argument is not the last argument, you will get an error.
Example
Having the ...
operator on the first of two arguments, will raise an error:
function myFamily(...$firstname, $lastname) {
$txt = "";
$len = count($firstname);
for($i = 0; $i < $len; $i++) {
$txt = $txt."Hi, $firstname[$i] $lastname.<br>";
}
return $txt;
}
$a = myFamily("Doe", "Jane", "John", "Joey");
echo $a;
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PHP is a Loosely Typed Language
In the examples 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
<?php declare(strict_types=1); // strict requirement
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 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
<?php declare(strict_types=1); // strict requirement
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
<?php declare(strict_types=1); // strict requirement
function addNumbers(float $a, float $b) : int {
return (int)($a + $b);
}
echo addNumbers(1.2, 5.2);
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