PHP gets the __FILE__ constant of the root directory_PHP tutorial

1. PHP's __FILE__ constant (how to get the root directory)

dirname(__FILE___) function returns the path where the script is located.
For example, the file b.php contains the following content:
$basedir = dirname(__FILE__);
?>
If b.php is referenced by a.php file require or include in other directories words.
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.

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 a . (current directory)
[The reason is that the b.php file is in http.conf or the default WEB directory of the PHP configuration development environment.
For example, WEB_ROOT is: "C :/root/www/".]
The path of the b.php file is: "C:/root/www/b.php". Usage tips, if you repeat it once, you can move the directory up a level:
For example: $d = dirname(dirname(__FILE__));
In fact, it just gives a directory as a parameter to dirname(). Because dirname() returns the last directory without \＼ or /
, when it is used repeatedly, it can be considered that dirname() treats the lowest directory as a file name. Return to
the upper-level directory of the current directory as usual. Repeat this to get its upper-level directory. Include the file that obtained the upper-level directory include(dirname(__FILE__).'/../filename.php'); 2. How to use PHP files and html files together if($reguser != ""){
echo"Submit Photo
";
echo "Log Out";
}else{
echo "Login";
}
?>

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