PHP system constant magic method description and magic variable usage example summary

System constants

FILE Current file name
LINE Current line number
FUNCTION Current function name
CLASS Current class name
METHOD Current object method Name

Detailed analysis

1. FILE

The full path and file name of the file. If used in an included file, returns the included file name. Since PHP 4.0.2, FILE always contains an absolute path (or the resolved absolute path in the case of a symbolic link), while versions before that sometimes contained a relative path.
PHP constant dirname(file)
FILE: Known as PHPmagic constant, returns the full path and file name of the currently executing PHP script, including an absolute path

1 ) The dirname(FILE) function returns the path where the script is located. Update the network
For example, the file b.php contains the following content:

<?php   
$basedir = dirname(FILE);   
echo $basedir  
//将在页面打印出一个这个文件所在绝对路径!  
?>

This is equivalent to the usage of server.mappth in asp
If b.php is required by the a.php file in other directories Or include to quote. The content of the variable $basedir is still the path to the folder where b.php is located. Instead of becoming the directory where the a.php file is located.

2) dirname(FILE) generally returns a directory structure from the current directory where the file is located to the system root directory.
The current file name will not be returned. dirname(FILE) may also return one. (current directory) [The reason is that the b.php file is in the default WEB directory of http.conf or PHP Configure development environment

<?php
/**
在你的公用的配置文件中，来设置你的根目录，这样就不用担心经常搬家了。
*/
define(&#39;ROOT_PATH&#39;, dirname(FILE) . DIRECTORY_SEPARATOR);
echo ROOT_PATH;
echo "<br>";
echo FILE;
echo "<br>";
echo dirname(FILE);
echo "<br>";
echo dirname(dirname(FILE));
?>

2. LINE

The current line number in the file. This variable is quite useful when debugging errors. At other times, it is of little use.

<?php
echo LINE;  //显示，LINE所在的行号
?>

3. CLASS
The name of the class, the result returned by PHP5 It is case-sensitive

<?php
class base_class
{
function say_a()
{
echo "&#39;a&#39; – said the " . CLASS . "<br/>";
}
function say_b()
{
echo "&#39;b&#39; – said the " . get_class($this) . "<br/>";
}
}
class derived_class extends base_class
{
function say_a()
{
parent::say_a();
echo "&#39;a&#39; – said the " . CLASS . "<br/>";
}
function say_b()
{
parent::say_b();
echo "&#39;b&#39; – said the " . get_class($this) . "<br/>";
}
}
$obj_b = new derived_class();
$obj_b->say_a();
echo "<br/>";
$obj_b->say_b();
?>

The result is:

'a' – said the base_class
'a' – said the derived_class
'b' – said the  derived_class
'b' – said the derived_class

Sometimes, we can use get_class instead of CLASS

4. FUNCTION and METHOD

FUNCTION: Function name, the result returned in php5 is case-sensitive
METHOD: Function name in the method, the result returned in php5 is case-sensitive
Two They are both the names of the methods, what's the difference?

<?php
class test
{
function a()
{
echo FUNCTION;
echo "<br>";
echo METHOD;
}
}
function good (){
echo FUNCTION;
echo "<br>";
echo METHOD;
}
$test = new test();
$test->a();
echo "<br>";
good();
?>

Return result:

a
test::a
good
good

Compared with the isolated function, both can take out the function name, there is no difference. If it is a method in the class, FUNCTION can only Get the method name of the class, and METHOD can not only get the method name, but also the directory where the class name

5. DIR

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)
If you want to use DIR in versions before 5.3, you can do this

<?php
if(!defined(&#39;DIR&#39;)) {
$iPos = strrpos(FILE, "/");
define("DIR", substr(FILE, 0, $iPos) . "/");
}
?>

6. NAMESPACE

currentThe name of the namespace (case sensitive). This constant is defined at compile time (new in PHP 5.3.0)

7. STATIC

#When you call the static method of class, return the class name, case sensitive. If called in inheritance, the inherited class name can be returned regardless of whether it is defined in inheritance.

<?php
//php5.3
class Model
{
public static function find()
{
echo STATIC;
}
}
class Product extends Model {}
class User extends Model {}
Product::find(); // "Product"
User::find(); // "User"
?>

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