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# PHP
[PHP Docs](https://www.php.net/docs.php)
```php
declare(strict_types=1); # activates variable type checking on function arguments
# single line comment
//single line comment
/* multi line comment */
```
## Include, Require
```php
include "path\\file.php"; # import an external php file, E_WARNING if fails
include_once "path\\file.php"; # imports only if not already loaded
require "path\\file.php"; # import an external php file, E_COMPILE_ERROR if fails
require_once "path\\file.php"; # imports only if not already loaded
```
### Import configs from a file with `include`
In `config.php`:
```php
//config.php
//store configuration options in associative array
return [
setting => value,
setting = value,
]
```
```php
$config = include "config.php"; // retrieve config and store into variable
```
## Namespace
[PSR-4 Spec](https://www.php-fig.org/psr/psr-4/)
```php
namespace Foo\Bar\Baz; # set namespace for all file contents, \ for nested namespaces
use <PHP_Class> # using a namespace hides standard php classes (WHY?!?)
# namespace for only a block of code
namespace Foo\Bar\Baz {
function func() {
# coded here
}
};
Foo\Bar\Baz\func(); # use function from Foo\Bar\Baz without USE instruction
use Foo\Bar\Baz\func; # import namespace
func(); # use function from Foo\Bar\Baz
use Foo\Bar\Baz\func as f; # use function with an alias
f(); # use function from Foo\Bar\Baz
use Foo\Bar\Baz as fbb # use namespace with alias
fnn\func(); # use function from Foo\Bar\Baz
```
## Basics
```php
declare(strict_types=1); # activates type checking
# single line comment
//single line comment
/* multi line comment */
```
### Screen Output
```php
echo "string"; # string output
echo 'string\n'; # raw string output
printf("format", $variables); # formatted output of strings and variables
sprintf("format", $variables); # return formatted string
```
### User Input
```php
$var = readline("prompt");
# if readline is not installed
if (!function_exists('readline')) {
function readline($prompt)
{
$fh = fopen('php://stdin', 'r');
echo $prompt;
$userInput = trim(fgets($fh));
fclose($fh);
return $userInput;
}
}
```
## Variables
```php
$variableName = value; # weakly typed
echo gettype(&variable); # output type of variable
var_dump($var); # prints info of variable (bit dimension, type & value)
```
### Integers
```php
&max = PHP_INT_MAX; # max value for int type -> 9223372036854775807
&min = PHP_INT_MIN; # min value for int type -> -9223372036854775808
&bytes = PHP_INT_SIZE; # bytes for int type -> 8
&num = 255; # decimal
&num = 0b11111111; # binary
&num = 0377; # octal
&num = 0xff; # hexadecimal
```
### Double
```php
$a = 1.234; // 1.234
$b = 1.2e3; // 1200
$c = 7E-10; // 0.0000000007
```
### Mathematical Operators
| Operator | Operation |
| -------- | -------------- |
| `-` | Subtraction |
| `*` | Multiplication |
| `/` | Division |
| `%` | Modulo |
| `**` | Exponentiation |
| `var++` | Post Increment |
| `++var` | Pre Increment |
| `var--` | Post Decrement |
| `--var` | Pre Decrement |
### Mathematical Functions
- `sqrt($x)`
- `sin($x)`
- `cos($x)`
- `log($x)`
- `round($x)`
- `floor($x)`
- `ceil($x)`
## Strings
A string is a sequence of ASCII characters. In PHP a string is an array of characters.
### String Concatenation
```php
$string1 . $string2; # method 1
$string1 .= $string2; # method 2
```
### String Functions
```php
strlen($string); # returns the string length
strpos($string, 'substring'); # position of substring in string
substr($string, start, len); # extract substring of len from position start
strtoupper($string); # transform to uppercase
strtolower($string); # transform to lowercase
explode(delimiter, string); # return array of substrings
$var = sprintf("format", $variables) # construct and return a formatted string
```
## Constants
```php
define ('CONSTANT_NAME', 'value')
```
### Magic Constants `__NAME__`
- `__FILE__`: script path + script filename
- `__DIR__`: file directory
- `__LINE__`: current line number
- `__FUNCTION__`: the function name, or {closure} for anonymous functions.
- `__CLASS__`: name of the class
- `__NAMESPACE__`: the name of the current namespace.
## Array
Heterogeneous sequence of values.
```php
$array = (sequence_of_items); # array declaration and valorization
$array = [sequence_of_items]; # array declaration and valorization
# index < 0 selects items starting from the last
$array[index]; # access to the items
$array[index] = value; # array valorization (can add items)
$array[] = value; # value appending
```
### Multi Dimensional Array (Matrix)
Array of array. Can have arbitrary number of nested array
```php
$matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
];
```
### Array Printing
Single instruction to print whole array is ``
```php
$array = [1, 2, 3];
print_r($array); # print all the array values
```
### Array Functions
```php
count($array); # returns number of items in the array
array_sum($array) # sum of the array value
sort($array); # quick sort
in_array($item, $array); // check if item is in the array
array_push($array, $item); // append item to the array
unset($array[index]); # item (or variable) deletion
# array navigation
current();
key();
next();
prev();
reset();
end();
# sorting
sort($array, $sort_flags="SORT_REGULAR");
array_values($array); # regenerates the array fixing the indexes
list($array1 [, $array2, ...]) = $data; # Python-like tuple unpacking
```
### Associative Arrays
Associative arrays have a value as an index. Alternative names are _hash tables_ or _dictionaries_.
```php
$italianDay = [
'Mon' => 'Lunedì',
'Tue' => 'Martedì',
'Wed' => 'Mercoledì',
'Thu' => 'Giovedì',
'Fri' => 'Venerdì',
'Sat' => 'Sabato',
'Sun' => 'Domenica'
];
$italianDay["Mon"]; # evaluates to Lunedì
```
## Conditional Instructions
### Conditional Operators
| Operator | Operation |
| ----------- | ------------------------ |
| $a `==` $b | value equality |
| $a `===` $b | value & type equality |
| $a `!=` $b | value inequality |
| $a `<>` $b | value inequality |
| $a `!==` $b | value or type inequality |
| $a `<` $b | less than |
| $a `>` $b | greater than |
| $a `<=` $b | less or equal to |
| $a `>=` $b | greater or equal to |
| $a `<=>` $b | spaceship operator |
With `==` a string evaluates to `0`.
### Logical Operators
| Operator | Example | Result |
| -------- | ----------- | ---------------------------------------------------- |
| `and` | `$a and $b` | TRUE if both `$a` and `$b` are TRUE. |
| `or` | `$a or $b` | TRUE if either `$a` or `$b` is TRUE. |
| `xor` | `$a xor $b` | TRUE if either `$a` or `$b` is TRUE, but _not both_. |
| `not` | `!$a` | TRUE if `$a` is _not_ TRUE. |
| `and` | `$a && $b` | TRUE if both `$a` and `$b` are TRUE. |
| `or` | `$a || $b` | TRUE if either `$a` or `$b` is TRUE. |
### Ternary Operator
```php
condition ? result_if_true : result_if_false;
condition ?: result_if_false;
```
### NULL Coalesce
```php
$var1 = $var2 ?? value; # if variable == NULL assign value, otherwise return value of $var2
# equivalent to
$var1 = isset($var2) ? $var2 : value
```
### Spaceship Operator
```php
$a <=> $b;
# equivalent to
if $a > $b
return 1;
if $a == $b
return 0;
if $a < $b
return -1;
```
### `If` - `Elseif` - `Else`
```php
if (condition) {
# code here
} elseif (condition) {
# code here
} else {
# code here
}
if (condition) :
# code here
elseif (condition):
# code here
else:
# code here
endif;
```
### Switch Case
```php
# weak comparison
switch ($var) {
case value:
# code here
break;
default:
# code here
}
# strong comparison
switch (true) {
case $var === value:
# code here
break;
default:
# code here
}
```
### Match Expression (PHP 8)
`match` can return values, doesn't require break statements, can combine conditions, uses strict type comparisons and doesn't do any type coercion.
```php
$result = match($input) {
0 => "hello",
'1', '2', '3' => "world",
};
```
## Loops
### For, Foreach
```php
for (init, condition, increment){
# code here
}
for (init, condition, increment):
# code here
endfor;
foreach($sequence as $item) {
# code here
}
foreach($sequence as $item):
# code here
endforeach;
# foreach on dicts
foreach($sequence as $key => $value) {
# code here
}
```
### While, Do-While
```php
while (condition) {
# code here
}
while (condition):
# code here
endwhile;
do {
# code here
} while (condition);
```
### Break, Continue, exit()
`break` stops the iteration.
`continue` skips one cycle of the iteration.
`exit()` terminates the execution of any PHP code.
## Functions
[Function Docstring](https://make.wordpress.org/core/handbook/best-practices/inline-documentation-standards/php/)
Parameters with default values are optional in the function call and must be the last ones in the function declaration. Return type is optional if type checking is disabled.
```php
declare(strict_types=1); # activates type checking
/**
* Summary.
*
* Description.
*
* @since x.x.x
*
* @see Function/method/class relied on
* @link URL
* @global type $varname Description.
* @global type $varname Description.
*
* @param type $var Description.
* @param type $var Optional. Description. Default.
* @return type Description.
*/
function functionName (type $parameter, $parameter = default_value): Type
{
# code here
return <expression>;
}
```
### Void function
```php
function functionName (type $parameter, $parameter = default_value): Void
{
# code here
}
```
### Passing a parameter by reference (`&$`)
```php
function functionName (type &$parameter): Type
{
# code here
return <expression>;
}
```
### Variable number of parameters, variadic operator (`...`)
```php
function functionName (type $parameter, ...$args): Type
function functionName (type $parameter, type ...$args): Type
{
# code here
return <expression>;
}
```
### Nullable parameters
```php
function functionName (?type $parameter): ?Type
{
# code here
return <expression>;
}
```
## Anonymous Functions (Closure)
```php
# declaration and assignment to variable
$var = function (type $parameter) {
# code here
};
$var($arg);
```
### Use Operator
```php
# use imports a variable into the closure
$foo = function (type $parameter) use ($average) {
# code here
}
```
### Union Types (PHP 8)
**Union types** are a collection of two or more types which indicate that _either_ one of those _can be used_.
```php
public function foo(Foo|Bar $input): int|float;
```
### Named Arguments (PHP 8)
Named arguments allow to pass in values to a function, by specifying the value name, to avoid taking their order into consideration.
It's also possible to skip optional parameters.
```php
function foo(string $a, string $b, ?string $c = null, ?string $d = null) { /* … */ }
foo(
b: 'value b',
a: 'value a',
d: 'value d',
);
```
## Object Oriented Programming
### Scope & Visibility
`public` methods and attributes are visible to anyone (_default_).
`private` methods and attributes are visible only inside the class in which are declared.
`protected` methods and attributes are visible only to child classes.
`final` classes cannot be extended.
### Class Declaration & Instantiation
```php
# case insensitive
class ClassName
{
const CONSTANT = value; # public by default
public $attribute; # null by default if not assigned
public Type $attribute; # specifying the type is optional, it will be enforced if present
# class constructor
public function __construct(value)
{
$this->attribute = value
}
public getAttribute(): Type
{
return $this->attribute;
}
public function func(): Type
{
# code here
}
}
$object = new ClassName; # case insensitive (CLASSNAME, ClassName, classname)
$object->attribute = value;
$object->func();
$object::CONSTANT;
$var = $object; # copy by reference
$var = clone $object # copy by value
$object instanceof ClassName // check type of the object
```
### Static classes, attributes & methods
Inside static methods it's impossible to use `$this`.
A static variable is unique for the class and all instances.
```php
class ClassName {
public static $var;
public static function func(){
//code here
}
public static function other_func(){
//code here
self::func();
}
}
ClassName::func(); // use static function
$obj = new ClassName();
$obj::$var; // access to the static variable
```
### [Dependency Injection](https://en.wikipedia.org/wiki/Dependency_injection)
Parameters of the dependency can be modified before passing the required class to the constructor.
```php
class ClassName
{
private $dependency;
public function __construct(ClassName requiredClass)
{
$this->dependency = requiredClass; # necessary class is passed to the constructor
}
}
```
### Inheritance
If a class is defined `final` it can't be extended.
If a function is declared `final` it can't be overridden.
```php
class Child extends Parent
{
public __construct() {
parent::__construct(); # call parent's method
}
}
```
### Abstract Class
Abstract classes cannot be instantiated;
```php
abstract class ClassName
{
# code here
}
```
### Interface
An interface is a "contract" that defines what methods the implementing classes **must** have and implement.
A class can implement multiple interfaces but there must be no methods in common between interface to avoid ambiguity.
```php
interface InterfaceName {
// it is possible to define __construct
// function has no body; must be implements in the class that uses the interface
public function functionName (parameters) : Type; // MUST be public
}
class ClassName implements InterfaceName {
public function functionName(parameters) : Type {
//implementation here
}
}
```
### Traits
`Traits` allows the reutilization of code inside different classes without links of inheritance.
It can be used to mitigate the problem of _multiple inheritance_, which is absent in PHP.
In case of functions name conflict it's possible to use `insteadof` to specify which function to use. It's also possible to use an _alias_ to resolve the conflicts.
```php
trait TraitName {
// code here
}
class ClassName {
use TraitName, {TraitName::func() insteadof OtherTrait}, { func() as alias }; # can use multiple traits
# code here
}
```
### Anonymous Classes
```php
$obj = new ClassName;
$obj->method(new class implements Interface {
public function InterfaceFunc() {
// code here
}
});
```
## Serialization & JSON
```php
$serialized = serialize($obj); # serialization
$obj = unserialize($serialized); # de-serialization
$var = json_decode(string $json, bool $associative); # Takes a JSON encoded string and converts it into a PHP variable.ù
$json = json_encode($value); # Returns a string containing the JSON representation of the supplied value.
```
## Files
### Read/Write on Files
```php
file(filename); // return file lines in an array
// problematic with large files (allocates memory to read all file, can fill RAM)
file_put_contents(filename, data); // write whole file
file_get_contents(filename); // read whole file
```
## Regular Expressions
```php
preg_match('/PATTERN/', string $subject, array $matches); # returns 1 if the pattern matches given subject, 0 if it does not, or FALSE if an error occurred
# $matches[0] = whole matched string
# $matches[i] = i-th group of the regex
```
## Hashing
Supported hashing algrithms:
- `md2`, `md4`, `md5`
- `sha1`, `sha224`, `sha256`, `sha384`, `sha512/224`, `sha512/256`, `sha512`
- `sha3-224`, `sha3-256`, `sha3-384`, `sha3-512`
- `ripemd128`, `ripemd160`, `ripemd256`, `ripemd320`
- `whirlpool`
- `tiger128,3`, `tiger160,3`, `tiger192,3`, `tiger128,4`, `tiger160,4`, `tiger192,4`
- `snefru`, `snefru256`
- `gost`, `gost-crypto`
- `adler32`
- `crc32`, `crc32b`, `crc32c`
- `fnv132`, `fnv1a32`, `fnv164`, `fnv1a64`
- `joaat`
- `haval128,3`, `haval160,3`, `haval192,3`, `haval224,3`, `haval256,3`, `haval128,4`, `haval160,4`, `haval192,4`, `haval224,4`, `haval256,4`, `haval128,5`, `haval160,5`, `haval192,5`, `haval224,5`, `haval256,5`
```php
hash($algorithm, $data);
```
### Password Hashes
`password_hash()` is compatible with `crypt()`. Therefore, password hashes created by `crypt()` can be used with `password_hash()`.
Algorithms currently supported:
- **PASSWORD_DEFAULT** - Use the _bcrypt_ algorithm (default as of PHP 5.5.0). Note that this constant is designed to change over time as new and stronger algorithms are added to PHP.
- **PASSWORD_BCRYPT** - Use the **CRYPT_BLOWFISH** algorithm to create the hash. This will produce a standard `crypt()` compatible hash using the "$2y$" identifier. The result will always be a 60 character string, or FALSE on failure.
- **PASSWORD_ARGON2I** - Use the **Argon2i** hashing algorithm to create the hash. This algorithm is only available if PHP has been compiled with Argon2 support.
- **PASSWORD_ARGON2ID** - Use the **Argon2id** hashing algorithm to create the hash. This algorithm is only available if PHP has been compiled with Argon2 support.
**Supported options for PASSWORD_BCRYPT**:
- **salt** (string) - to manually provide a salt to use when hashing the password. Note that this will override and prevent a salt from being automatically generated.
If omitted, a random salt will be generated by password_hash() for each password hashed. This is the intended mode of operation.
**Warning**: The salt option has been deprecated as of PHP 7.0.0. It is now preferred to simply use the salt that is generated by default.
- **cost** (integer) - which denotes the algorithmic cost that should be used. Examples of these values can be found on the crypt() page.
If omitted, a default value of 10 will be used. This is a good baseline cost, but you may want to consider increasing it depending on your hardware.
**Supported options for PASSWORD_ARGON2I and PASSWORD_ARGON2ID**:
- **memory_cost** (integer) - Maximum memory (in kibibytes) that may be used to compute the Argon2 hash. Defaults to PASSWORD_ARGON2_DEFAULT_MEMORY_COST.
- **time_cost** (integer) - Maximum amount of time it may take to compute the Argon2 hash. Defaults to PASSWORD_ARGON2_DEFAULT_TIME_COST.
- **threads** (integer) - Number of threads to use for computing the Argon2 hash. Defaults to PASSWORD_ARGON2_DEFAULT_THREADS.
```php
password_hash($password, $algorithm); # create a new password hash using a strong one-way hashing algorithm.
password_verify($password, $hash); # Verifies that a password matches a hash
```
## Errors
Types of PHP errors:
- **Fatal Error**: stop the execution of the program.
- **Warning**: generated at runtime, does not stop the execution (non-blocking).
- **Notice**: informative errors or messages, non-blocking.
```php
$a = new StdClass()
$a->foo(); // PHP Fatal Error: foo() does not exist
```
```php
$a = 0;
echo 1/$a; // PHP Warning: Division by zero
```
```php
echo $a; // PHP Notice: $a undefined
```
### Error Reporting
[PHP Error Constants](https://www.php.net/manual/en/errorfunc.constants.php)
Its possible to configure PHP to signal only some type of errors. Errors below a certain levels are ignored.
```php
error_reporting(E_<type>); // set error report threshold (for log file)
// does not disable PARSER ERROR
ini_set("display_errors", 0); // don't display any errors on stderr
ini_set("error_log", "path\\error.log"); // set log file
```
### Triggering Errors
```php
// generate E_USER_ errors
trigger_error("message"); // default type: E_USER_NOTICE
trigger_error("message", E_USER_<Type>);
trigger_error("Deprecated Function", E_USER_DEPRECATED);
```
### [Writing in the Log File](https://www.php.net/manual/en/function.error-log.php)
It's possible to use log files unrelated to the php log file.
```php
error_log("message", 3, "path\\log.log"); // write log message to a specified file
//example
error_log(sprintf("[%s] Error: _", date("Y-m-d h:i:s")), 3, "path\\log.log")
```
## Exception Handling
PHP offers the possibility to handle errors with the _exception model_.
```php
try {
// dangerous code
} catch(ExceptionType1 | ExceptionType2 $e) {
printf("Errore: %s", $e->getMessage());
} catch(Exception $e) {
// handle or report exception
}
throw new ExceptionType("message"); // throw an exception
```
All exceptions in PHP implement the interface `Throwable`.
```php
Interface Throwable {
abstract public string getMessage ( void )
abstract public int getCode ( void )
abstract public string getFile ( void )
abstract public int getLine ( void )
abstract public array getTrace ( void )
abstract public string getTraceAsString ( void )
abstract public Throwable getPrevious ( void )
abstract public string __toString ( void )
}
```
### Custom Exceptions
```php
/**
* Define a custom exception class
*/
class CustomException extends Exception
{
// Redefine the exception so message isn't optional
public function __construct($message, $code = 0, Exception $previous = null) {
// some code
// make sure everything is assigned properly
parent::__construct($message, $code, $previous);
}
// custom string representation of object
public function __toString() {
return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
}
public function customFunction() {
echo "A custom function for this type of exception\n";
}
}
```