Detailed introduction and examples of PHP magic constants, magic functions, and predefined constants

1. Magic constants

1、__construct()

Instantiation object, when __construct and a function with the class name and function name exist at the same time, __construct will be called and the other will not be called.

2, __destruct()

Called when an object is deleted or the object operation terminates

3, __call()

The object calls a method. If the method exists, it will be called directly; if it does not exist, the __call function will be called

4, __get()

When reading the attributes of an object, if the attribute exists, the attribute value will be returned directly; if it does not exist, the __get function will be called.

5. __set()
When setting the attributes of an object, if the attribute exists, the value will be assigned directly; if it does not exist, the __set function will be called.

6. __toString()
Called when printing an object. Such as echo $obj; or print $obj;

7, __clone()
is called when cloning an object. For example: $t=new Test();$t1=clone $t;

8, __sleep()
serialize was called before. If the object is relatively large and you want to delete a little bit before serializing it, you can consider this function.

9. __wakeup()
is called when unserialize and does some object initialization work.

10. __isset()
Called when detecting whether an object's attributes exist. For example: isset($c->name).

11. __unset()
Called when unsetting the properties of an object. For example: unset($c->name).

12. __set_state()
Called when var_export is called. Use the return value of __set_state as the return value of var_export.

13. __autoload()
When instantiating an object, if the corresponding class does not exist, this method is called.

Example:

1, __get() Called when trying to read a property that does not exist.

If you try to read a property that does not exist in an object, PHP will give an error message. If we add the __get method to the class, we can use this function to implement various operations similar to reflection in Java.

class Test 
{ 
     public function __get($key) 
    { 
         echo $key . " 不存在"; 
    } 
} 

$t = new Test(); 
echo $t->name; 
输出：name不存在

2, __set() Called when trying to write a value to a property that does not exist.

class Test 
{ 
    public function __set($key, $value) 
    { 
         echo '对' . $key . "附值" . $value; 
    } 
} 

$t = new Test(); 
$t->name = "aninggo"; 
输出：对name赋值aninggo

3, __call() This method is called when trying to call a method that does not exist on the object.

class Test 
{ 
    public function __call($Key, $Args) 
    { 
         echo "您要调用的 {$Key} 方法不存在。你传入的参数是：" . print_r($Args, true); 
    } 
} 

$t = new Test(); 
$t->getName(aning, go);

程序将会输出：
您要调用的 getName 方法不存在。参数是：Array
(
     [0] => aning
     [1] => go
)

4, __toString() is called when printing an object. This method is similar to java's toString method. This function is called back when we print the object directly.

class Test 
{ 
     public function __toString() 
     { 
         return "打印 Test"; 
     } 
} 

$t = new Test(); 
echo $t;

When echo $t; is run, $t->__toString(); will be called and the program will output: print Test;

5,__clone() Called when the object is cloned.

class Test 
{ 
     public function __clone() 
     { 
         echo "我被复制了！"; 
     }
}

$t = new Test(); 
$t1 = clone $t;

程序输出：我被复制了！

2. Magic constants

1. __LINE__
Returns the current line number in the file.
2, __FILE__
Return the full path and file name of the file. If used in an include file, returns the include file name. As of PHP 4.0.2, __FILE__ always contains an absolute path, while versions before that sometimes contained a relative path.

3, __DIR__
The directory where the file is located. If used within an included file, returns the directory where the included file is located. It is equivalent to dirname(__FILE__). Directory names do not include the trailing slash unless they are the root directory. (New in PHP 5.3.0)
4, __FUNCTION__
Returns the function name (New in PHP 4.3.0). Since PHP 5 this constant returns the name of the function as it was defined (case sensitive). In PHP 4 this value is always lowercase.
5, __CLASS__
Returns the name of the class (newly added in PHP 4.3.0). Since PHP 5 this constant returns the name of the class when it was defined (case sensitive). In PHP 4 this value is always lowercase.

6, __TRAIT__
The name of Trait (newly added in PHP 5.4.0). Since PHP 5.4 this constant returns the name of the trait as it was defined (case-sensitive). The trait name includes the scope in which it is declared (e.g. Foo\Bar).
7, __METHOD__
Returns the method name of the class (newly added in PHP 5.0.0). Returns the name of the method as it was defined (case-sensitive). Format: Class name::Method name

8, __NAMESPACE__
The name of the current namespace (case-sensitive). This constant is defined at compile time (new in PHP 5.3.0)

3. Predefined constants

PHP_VERSION The version of the PHP program, such as 4.0.2
PHP_OS The name of the operating system that executes the PHP interpreter, such as Windows
PHP_SAPI It is used to determine whether it is executed by a command line or a browser. #                                                                                                                                                                                                                                                                   
PHP_EOL System newline character, Windows is (\r\n), Linux is (/n), MAC is (\r), available since PHP 4.3.10 and PHP 5.0.2
DIRECTORY_SEPARATOR System Directory separators, Windows is anti -slope (\), linux is oblique line (/)
Path_Separat Multi -path interval symbol, Windows is anti -slope (), linux is a slash ( :)
Qp_int_max int value, the 32 -bit platform value is 2147483647, from PHP 4.4.0 and PHP 5.0.5 can be available from
» The value for 32-bit platforms is 4 (4 bytes), available from PHP 4.4.0 and PHP 5.0.54. PHP running environment detection function
php_sapi_name()
This function returns a lowercase string describing the interface between PHP and the WEB server. Returns a lowercase string describing the interface type used by PHP (the Server API, SAPI). For example, under CLI PHP this string will be "cli", under Apache there may be several different values, depending on the specific SAPI used.
Possible values ​​are listed below: aolserver, apache, apache2filter, apache2handler, caudium, cgi (until PHP 5.3), cgi-fcgi, cli, continuity, embed, isapi, litespeed, milter, nsapi, phttpd , pi3web, roxen, thttpd, tux and webjames. SAPI: Server-side API, seems to be the same thing as CGI. The API provided by each server may be different, but they all provide CGI.
So it can be understood that CGI is a SAPI that every server should have. Apache has its own SAPI, and IIS also has its own. But php can work on these different servers because php supports their respective SAPIs. PHP-CLI: php command line interface, php can work in this mode or CGI mode. It is a kind of SAPI, which has similar functions to CGI.

If you want to know more about the relevant content or want to better master these functions and constants, please visit the PHP Chinese website:

PHP Video Tutorial

The above is the detailed content of Detailed introduction and examples of PHP magic constants, magic functions, and predefined constants. For more information, please follow other related articles on the PHP Chinese website!