Functions

Built-in functions

PHP contains lots of built-in functions
We restrict ourselves to some useful array, string and date functions

Array functions

Complete list of array functions
Open course/array_functions.php

Function	Comment
`in_array($value, $array)`	checks if a specified `$value` exists in an `$array`
`asort($array)`	sort `$array` in ascending order and maintain index association (important with associative arrays!)
`arsort($array)`	sort `$array` in descending order and maintain index association (important with associative arrays!)
`ksort($array)`	Sort `$array` by key in ascending order
`krsort($array)`	sort `$array` by key in descending order
`array_push($array, $values)`	push one or more `$values` onto the end `$array`
`array_unshift($array, $values)`	prepend one or more `$values` to the beginning of `$array`
`implode($separator, $array)`	join `$array` elements with a `$separator` string
`compact()`	create an array containing variables and their values

php

<article>
    <h2>in_array()</h2>
    <?php
    $students = ['Doe, John' => 'r0662335', 'Doe, Jane' => 'r0715283', 'Smith, Jeff' => 'r0622915'];
    $search = 'r06229152';

    $found = in_array($search, $students) ? ' found ' : ' not found ';
    echo "<p> Student with r-number $search was <b>$found</b>. </p>\n";
    ?>
</article>

<article>
    <h2>in_array()</h2>
    <?php
    $students = ['Doe, John' => 'r0662335', 'Doe, Jane' => 'r0715283', 'Smith, Jeff' => 'r0622915'];
    $search = 'r06229152';

    $found = in_array($search, $students) ? ' found ' : ' not found ';
    echo "<p> Student with r-number $search was <b>$found</b>. </p>\n";
    ?>
</article>

in_array

String functions

Complete list of string functions
Open course/string_functions.php

Function	Comment
`strlen($string)`	returns the length of `$string`
`strpos($haystack, $needle)`	returns the position of the string `$needle` in the string `$haystack`
`ucfirst($string)`	returns a string in which the first letter of $string is capitalized
`substr($string, $start, $length)`	returns a portion (with `$length` characters) of `$string`, starting from position `$start`
`str_replace($search, $replace, $string)`	returns a string with all occurrences of `$search` in `$string` replaced by `$replace`
`strtoupper($string)`	make `$string` and uppercase
`strtolower($string)`	make `$string` and lowercase
`ucwords($string)`	uppercase the first character of each word in `$string`
`explode($delimiter, $string)`	returns an array of strings, each of which is a substring of `$string` and which are separated by `$delimiter`
`number_format($number, $decimals, $decimalPoint, $thousandsSeparator)`	returns a string with a formatted version of `$number`, specified by the number of `$decimals`, the `$decimalPoint` and the `$thousandsSeparator`
`str_starts_with($haystack, $needle)` (PHP 8)	determine if a `$haystack` starts with a given `$needle`
`str_contains($haystack, $needle)` (PHP 8)	determine if a `$haystack` contains a given `$needle`
`str_ends_with($haystack, $needle)` (PHP 8)	determine if a `$haystack` ends with a given `$needle`

php

<article>
    <?php
    $testString = 'this is a random string to illustrate PHP string functions';

    echo "<p> Length of \$testString = " . strlen($testString) . "</p>\n";
    echo "<p> Position (first occurrence!) of 'is' in \$testString = " . strpos($testString, 'is') . "</p>\n";

    $testString = ucfirst($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $subString = substr($testString, strpos($testString, 'P'), 3);
    echo "<p> \$subString = <code>$subString</code></p>\n";

    $testString = str_replace('PHP', 'some', $testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";
    
    $testString = strtoupper($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $testString = strtolower($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $testString = ucwords($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $words = explode(' ', $testString);
    echo "<p> \$words = </p>\n";
    var_dump($words);
    ?>
</article>

<article>
    <?php
    $testString = 'this is a random string to illustrate PHP string functions';

    echo "<p> Length of \$testString = " . strlen($testString) . "</p>\n";
    echo "<p> Position (first occurrence!) of 'is' in \$testString = " . strpos($testString, 'is') . "</p>\n";

    $testString = ucfirst($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $subString = substr($testString, strpos($testString, 'P'), 3);
    echo "<p> \$subString = <code>$subString</code></p>\n";

    $testString = str_replace('PHP', 'some', $testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";
    
    $testString = strtoupper($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $testString = strtolower($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $testString = ucwords($testString);
    echo "<p> \$testString = <code>$testString</code></p>\n";

    $words = explode(' ', $testString);
    echo "<p> \$words = </p>\n";
    var_dump($words);
    ?>
</article>

Regular sting functions

Date/time functions

Complete list of date/time functions
Open course/date_functions.php

Function	Comment
`mktime($hour,$minute,$second,$month,$day,$year)`	get Unix timestamp for a date
`date("format", $timestamp)`	format a local time/date
`time()`	return current Unix timestamp

php

<article>
    <?php
    $timestamp = mktime(0, 0, 0, 12, 25, 2022); //25-12-2022, 0u00
    echo "<p> Christmas 2022 (" . date("d/m/Y", $timestamp) . ") falls on a " . date("l", $timestamp) . "</p>\n";

    echo "<p> Now, we are " . date("D d-m-Y, H:i:s") . "<br>"
      . time() . " seconds have passed since January 1, 1970, 00:00:00 </p>\n";

    $within4weeks = mktime(0, 0, 0, date("m"), date("d") + 28, date("Y"));
    echo "<p> Within 4 weeks, we are " . date("l d F 'y", $within4weeks) . "</p>\n";
    ?>
</article>

<article>
    <?php
    $timestamp = mktime(0, 0, 0, 12, 25, 2022); //25-12-2022, 0u00
    echo "<p> Christmas 2022 (" . date("d/m/Y", $timestamp) . ") falls on a " . date("l", $timestamp) . "</p>\n";

    echo "<p> Now, we are " . date("D d-m-Y, H:i:s") . "<br>"
      . time() . " seconds have passed since January 1, 1970, 00:00:00 </p>\n";

    $within4weeks = mktime(0, 0, 0, date("m"), date("d") + 28, date("Y"));
    echo "<p> Within 4 weeks, we are " . date("l d F 'y", $within4weeks) . "</p>\n";
    ?>
</article>

With the date("format", $timestamp) function, this $timestamp is converted into a readable format
- Using date("format") - without timestamp - we get the current date/time on the server
- Some format characters:

format character	description	values
d	day of the month with leading zeros	01 - 31
D	textual representation (three letters) of the day	Mon - Sun
j	day of the month without leading zeros	1 - 31
l	full textual representation of the day	Monday - Sunday
F	full textual representation of the month	January - December
m	numerical representation of the month with leading zeros	01 - 12
M	textual representation (three letters) of the month	Jan - Dec
n	numerical representation of the month without leading zeros	1 - 12
Y	numerical representation (4 digits) of a year	1970, 2019
y	numerical representation (2 digits) of a year	70, 19
h	12-hour format with leading zeros	01 - 12
H	24-hour format with leading zeros	00 - 23
i	minutes with leading zeros	00 - 59
s	seconds with leading zeros	00 - 59

REMARK

Probably, there is a time difference between the depicted time (on the server) and the local time, because the timezone on the server is incorrect. You can set the default timezone on the server to the correct timezone by adding the statement date_default_timezone_set('Europe/Brussels'), e.g. to the file shared/meta.php (included on every page).

User-defined functions

Open course/user_defined_functions.php

php

<?php
function writeMessage(): void
{
    echo "<p> We hope you like this PHP course! </p>\n";
}

function writePersonalMessage(string $name): void
{
    echo "<p> Dear $name, we hope you like this PHP course! </p>\n";
}

function writePersonalMessageWithDefault(string $name = 'Mr./Mrs.'): void
{
    echo "<p> Dear $name, we hope you like this PHP course! </p>\n";
}

function subtractReduction20(float $price): void
{
    $price *= 0.8;
}

function subtractReduction30(float &$price): void
{
    $price *= 0.7;
}

function average(float $number1, float $number2): float
{
    return ($number1 + $number2) / 2;
}
?>

<article>
    <?php
    writeMessage();
    writePersonalMessage('John');
    writePersonalMessageWithDefault('Jane');
    writePersonalMessageWithDefault();


    $price = 1000;
    subtractReduction20($price);
    echo "<p> Price with 20% reduction = " . $price . "</p>\n";

    $price = 1000;
    subtractReduction30($price);
    echo "<p> Price with 30% reduction = " . $price . "</p>\n";

    echo "<p> Average of 10 and 100 = " . average(10, 100) . "</p>\n";
    ?>
</article>

<?php
function writeMessage(): void
{
    echo "<p> We hope you like this PHP course! </p>\n";
}

function writePersonalMessage(string $name): void
{
    echo "<p> Dear $name, we hope you like this PHP course! </p>\n";
}

function writePersonalMessageWithDefault(string $name = 'Mr./Mrs.'): void
{
    echo "<p> Dear $name, we hope you like this PHP course! </p>\n";
}

function subtractReduction20(float $price): void
{
    $price *= 0.8;
}

function subtractReduction30(float &$price): void
{
    $price *= 0.7;
}

function average(float $number1, float $number2): float
{
    return ($number1 + $number2) / 2;
}
?>

<article>
    <?php
    writeMessage();
    writePersonalMessage('John');
    writePersonalMessageWithDefault('Jane');
    writePersonalMessageWithDefault();


    $price = 1000;
    subtractReduction20($price);
    echo "<p> Price with 20% reduction = " . $price . "</p>\n";

    $price = 1000;
    subtractReduction30($price);
    echo "<p> Price with 30% reduction = " . $price . "</p>\n";

    echo "<p> Average of 10 and 100 = " . average(10, 100) . "</p>\n";
    ?>
</article>

Functions without parameters

A user-defined function (e.g. function writeMessage(): void) starts with the keyword function, followed by( ) and his return value :void
The function code should be placed between { }

Functions with parameters

Put the parameters of a function between the round brackets, as in function writePersonalMessage(string $name): void
When a function with parameters is called (e.g. writePersonalMessage('John');), we need to supply arguments (the string 'John') to pass to the parameters ($name)
These parameters work like variables inside your function

Default values for parameters

You can set a parameter to have a default value if no argument is passed to the function, as in writePersonalMessageWithDefault(string $name = 'Mr./Mrs.'): void

By value versus by reference

By default, arguments are passed by value
- This means that the original value of a variable is not changed when you pass it as an argument to a function in which it is changed. See e.g. function subtractReduction20(float $price): void
You can pass a variable to a function by reference, meaning that the original value can be changed in the function
- In order to do so, precede the parameter in the function definition with &, as illustrated in
  subtractReduction30(float &$price): void

Functions with return value

A function can return a value using the return statement, as illustrated in
function average(float $number1, float $number2): float

Short arrow function

A short arrow function is a function with a single statement in the body
- works only for anonymous functions
- they start with the fn keyword
- the return keyword is not allowed
- arguments and return types can be type hinted

php

// long version
function(arguments)
{ 
  return expression;
}

// short version
fn(arguments) => expression;

// long version
function(arguments)
{ 
  return expression;
}

// short version
fn(arguments) => expression;

Type hinting

PHP, like many other programming languages, supports (optional) type hinting to specify the expected data type of an argument and return value in a function/class declaration
- PHP will check whether or not the arguments are of the specified type
- If not, the run-time will raise an error and execution will be halted

php

<article>
    <h2>Function with type hinting</h2>
    <?php
    function sum1(int $a, int $b): int
    {
        return $a + $b;
    }

    echo "<p>" . sum1(2, 3) . "</p>";
    echo "<p>" . sum1(2, 3.1) . "</p>";
    echo "<p>" . sum1(2, '3') . "</p>";
    ?>
</article>

<article>
    <h2>Function with type hinting</h2>
    <?php
    function sum1(int $a, int $b): int
    {
        return $a + $b;
    }

    echo "<p>" . sum1(2, 3) . "</p>";
    echo "<p>" . sum1(2, 3.1) . "</p>";
    echo "<p>" . sum1(2, '3') . "</p>";
    ?>
</article>

Function with type hinting

REMARK

Before PHP 8, union types could only be specified in phpdoc annotation comments.
Now this can be made directly as type hint by specifying the allowed value types in a list separated by the pipe symbol '|'.
Nullable types, which allow variables or return values to be either of a specific type or null, can be indicated using the ? prefix before the type name. For example, ?int represents an integer or null.
List of type hint in PHP function parameters and return values

Include

Often, you want to use your self-written functions in different PHP files
- Move the function definitions to a separate file (e.g. course/my_functions.php)
- Include the content of this file (with the function definitions) in the file course/user_defined_functions.php with the statement include_once 'my_functions.php'

REMARKS

It's a good practice to use this technique (of including files) to include a navigation menu, a footer, ... on every page of your application
- In our project, shared meta-data (shared/meta.php), a navigation bar (shared/nav.php) and a footer (shared/footer.php) are included on every page
Notice that we use relative paths in our include_once statements (e.g. include_once('../shared/meta.php')).
You might want to try include_once('/shared/meta.php'), but this doesn't work as in PHP the starting forward slash / does not correspond to the root of your project, but to the root of your filesystem on the server.
Use include_once($_SERVER['DOCUMENT_ROOT'] . '/shared/meta.php') to build up paths from the root of your project.
Read more on https://phpdelusions.net/articles/paths.

Functions ​

Built-in functions ​

Array functions ​

String functions ​

Date/time functions ​

User-defined functions ​

Functions without parameters ​

Functions with parameters ​

Default values for parameters ​

By value versus by reference ​

Functions with return value ​

Short arrow function ​

Type hinting ​

Include ​