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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 thePHP 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 "$fname Refsnes.<br>";
}
familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
The following example has a function with two arguments ($fname, $year):
Example
function familyName($fname, $year) {
echo "$fname Refsnes. Born in $year <br>";
}
familyName("Hege", "1975");
familyName("Stale", "1978");
familyName("Kai Jim", "1983");
PHP Default Argument Value
The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:
Example
function setHeight($minheight = 50) {
echo "The height is : $minheight <br>";
}
setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
PHP Functions - Returning values
To let a function return a value, use the return statement:
Example
function sum($x, $y) {
<span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">z = </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal" style="margin-right:0.04398em;">z</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>x + $y;
return $z;
}
echo "5 + 10 = " . sum(5, 10) . "<br>";
echo "7 + 13 = " . sum(7, 13) . "<br>";
echo "2 + 4 = " . sum(2, 4);
Passing Arguments by Reference
In PHP, arguments are usually passed by value, which means that a copy of the value is used in the function and the variable that was passed into the function cannot be changed.
When a function argument is passed by reference, changes to the argument also change the variable that was passed in. To turn a function argument into a reference, the &operator is used:
Example
Use a pass-by-reference argument to update a variable:
function add_five(&$value) {
$value += 5;
}
$num = 2;
add_five($num);
echo $num;
Variable Number of Arguments
By using the ... operator in front of the function parameter, the function accepts an unknown number of arguments. This is also called a variadic function.
The variadic function argument becomes an array.
Example
A function that do not know how many arguments it will get:
function sumMyNumbers(...$x) {
$n = 0;
<span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>e</mi><mi>n</mi><mo>=</mo><mi>c</mi><mi>o</mi><mi>u</mi><mi>n</mi><mi>t</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">len = count(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">co</span><span class="mord mathnormal">u</span><span class="mord mathnormal">n</span><span class="mord mathnormal">t</span><span class="mopen">(</span></span></span></span>x);
for($i = 0; <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>i</mi><mo><</mo></mrow><annotation encoding="application/x-tex">i < </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6986em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">i</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"><</span></span></span></span>len; $i++) {
<span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>n</mi><mo>+</mo><mo>=</mo></mrow><annotation encoding="application/x-tex">n += </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6667em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">n</span><span class="mord">+</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>x[$i];
}
return $n;
}
$a = sumMyNumbers(5, 2, 6, 2, 7, 7);
echo $a;
You can only have one argument with variable length, and it has to be the last argument.
Example
The variadic argument must be the last argument:
function myFamily($lastname, ...$firstname) {
$txt = "";
<span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>e</mi><mi>n</mi><mo>=</mo><mi>c</mi><mi>o</mi><mi>u</mi><mi>n</mi><mi>t</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">len = count(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">co</span><span class="mord mathnormal">u</span><span class="mord mathnormal">n</span><span class="mord mathnormal">t</span><span class="mopen">(</span></span></span></span>firstname);
for($i = 0; <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>i</mi><mo><</mo></mrow><annotation encoding="application/x-tex">i < </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6986em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">i</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"><</span></span></span></span>len; $i++) {
<span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>x</mi><mi>t</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">txt = </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6151em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">x</span><span class="mord mathnormal">t</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>txt."Hi, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>i</mi><mi>r</mi><mi>s</mi><mi>t</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>e</mi><mo stretchy="false">[</mo></mrow><annotation encoding="application/x-tex">firstname[</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal">i</span><span class="mord mathnormal">rs</span><span class="mord mathnormal">t</span><span class="mord mathnormal">nam</span><span class="mord mathnormal">e</span><span class="mopen">[</span></span></span></span>i] $lastname.<br>";
}
return $txt;
}
$a = myFamily("Doe", "Jane", "John", "Joey");
echo $a;
If the variadic argument is not the last argument, you will get an error.
Example
Having the ... operator on the first of two arguments, will raise an error:
function myFamily(...$firstname, $lastname) {
$txt = "";
<span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>l</mi><mi>e</mi><mi>n</mi><mo>=</mo><mi>c</mi><mi>o</mi><mi>u</mi><mi>n</mi><mi>t</mi><mo stretchy="false">(</mo></mrow><annotation encoding="application/x-tex">len = count(</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">e</span><span class="mord mathnormal">n</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal">co</span><span class="mord mathnormal">u</span><span class="mord mathnormal">n</span><span class="mord mathnormal">t</span><span class="mopen">(</span></span></span></span>firstname);
for($i = 0; <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>i</mi><mo><</mo></mrow><annotation encoding="application/x-tex">i < </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6986em;vertical-align:-0.0391em;"></span><span class="mord mathnormal">i</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel"><</span></span></span></span>len; $i++) {
<span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>t</mi><mi>x</mi><mi>t</mi><mo>=</mo></mrow><annotation encoding="application/x-tex">txt = </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6151em;"></span><span class="mord mathnormal">t</span><span class="mord mathnormal">x</span><span class="mord mathnormal">t</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span></span></span></span>txt."Hi, <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mi>i</mi><mi>r</mi><mi>s</mi><mi>t</mi><mi>n</mi><mi>a</mi><mi>m</mi><mi>e</mi><mo stretchy="false">[</mo></mrow><annotation encoding="application/x-tex">firstname[</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal">i</span><span class="mord mathnormal">rs</span><span class="mord mathnormal">t</span><span class="mord mathnormal">nam</span><span class="mord mathnormal">e</span><span class="mopen">[</span></span></span></span>i] $lastname.<br>";
}
return $txt;
}
$a = myFamily("Doe", "Jane", "John", "Joey");
echo $a;
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 strictdeclaration, 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 <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo separator="true">,</mo><mi>i</mi><mi>n</mi><mi>t</mi></mrow><annotation encoding="application/x-tex">a, int </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.854em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">a</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">in</span><span class="mord mathnormal">t</span></span></span></span>b) {
return <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>+</mo></mrow><annotation encoding="application/x-tex">a + </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6667em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">a</span><span class="mord">+</span></span></span></span>b;
}
echo addNumbers(5, "5 days");
// since strict is NOT enabled "5 days" is changed to int(5), and it will return 10
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 strictdeclaration:
Example
<?php declare(strict_types=1); // strict requirement
function addNumbers(int <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo separator="true">,</mo><mi>i</mi><mi>n</mi><mi>t</mi></mrow><annotation encoding="application/x-tex">a, int </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.854em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">a</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal">in</span><span class="mord mathnormal">t</span></span></span></span>b) {
return <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>+</mo></mrow><annotation encoding="application/x-tex">a + </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6667em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">a</span><span class="mord">+</span></span></span></span>b;
}
echo addNumbers(5, "5 days");
// since strict is enabled and "5 days" is not an integer, an error will be thrown
?>The strict declaration forces things to be used in the intended way.
PHP Return Type Declarations
PHP 7 also supports Type Declarations for the returnstatement. 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 <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo separator="true">,</mo><mi>f</mi><mi>l</mi><mi>o</mi><mi>a</mi><mi>t</mi></mrow><annotation encoding="application/x-tex">a, float </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">a</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">o</span><span class="mord mathnormal">a</span><span class="mord mathnormal">t</span></span></span></span>b) : float {
return <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>+</mo></mrow><annotation encoding="application/x-tex">a + </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6667em;vertical-align:-0.0833em;"></span><span class="mord mathnormal">a</span><span class="mord">+</span></span></span></span>b;
}
echo addNumbers(1.2, 5.2);
?>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 <span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo separator="true">,</mo><mi>f</mi><mi>l</mi><mi>o</mi><mi>a</mi><mi>t</mi></mrow><annotation encoding="application/x-tex">a, float </annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8889em;vertical-align:-0.1944em;"></span><span class="mord mathnormal">a</span><span class="mpunct">,</span><span class="mspace" style="margin-right:0.1667em;"></span><span class="mord mathnormal" style="margin-right:0.10764em;">f</span><span class="mord mathnormal" style="margin-right:0.01968em;">l</span><span class="mord mathnormal">o</span><span class="mord mathnormal">a</span><span class="mord mathnormal">t</span></span></span></span>b) : int {
return (int)($a + $b);
}
echo addNumbers(1.2, 5.2);
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