What beginners should know about PHP

Start and end tags

1. Two commonly used ones: ,

2. ##Short tag:

   , you need to open the short_open_tag command of the php.ini file

3. ASP style tag:

   <% %>, you need to open the asp_tags directive of the php.ini file

##php data type (9 Kinds)

Four scalar types

• integer

• float

• string

• object

• callable

##resource

• NULL (no type)

Pseudo-type

mixed )

• number (number type)

• callback (callback type, also called callable)

• array|object

• void

• ##pseudovariable$...

1. Type detection function (is_type), eg:

   is_string($str)

2. ##Super global variable

$GLOBALS

$_SERVER: Save information about headers, paths, script locations, etc.

• ##$_REQUEST: Collect data submitted by html forms

• $_POST

• $_GET

• $_FILES

• $_ENV

• $_COOKIE

• $_SESSION

• Access global variables within the function body

• global $variable_name

• Set constants

• define(const_name, const_value, boolean)

• boolean: constant names are case-sensitive, default false is sensitive, true is insensitive

• Create array
array()

• Get the array length

  count($arr)

• Array sorting : ascending order

  sort(), descending order rsort()

• Array key sorting: ascending order ksort(), descending order krsort()

• Array value sorting: ascending asort(), descending arsort()

• foreach loop (only for arrays)

foreach($array as $value) {}

• foreach($array as $key => $value) {}

• Magic variable

__LINE__

• __FILE__: Full path and file name of the file

• __DIR__: The directory where the file is located

• __FUNCTION__: Function name

• __METHOD__: The method name of the class

• __NAMESPACE__: The name of the current namespace

• Object-oriented
  Classes are defined using the class keyword followed by the class name

• Variables of the class are declared using var. Variables can also be initialized with values.

• Function definition is similar to the definition of the PHP function, but can only be passed This class and its instantiated objects access

• Constructor
function __construct($arg1, $arg2, ...)
• , mainly used to initialize objects

• Destructor

  function __destruct(), called at the end of the object’s life cycle, can destroy variables

• Inheritance

  extends, PHP does not support multiple inheritance

• Method rewriting, subclasses can rewrite parent class methods to meet needs
  Yes Access control of properties or methods:
public
• ,

  protected

  ,
private

• Interfaceinterface

• Constants are defined with

  const, no need for $

##Abstract class

• Attributes or methods declared as static can be accessed directly without instantiating the class

• The parent class method is declared final and cannot be overridden or inherited by subclasses

• Subclass calls parent class constructor method

  parent::__construct()

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