PHP Tutorial Tutorials PHP Constants

PHP Constants

Constants are used for storing fixed values. Once they are defined, they cannot be undefined or changed.
The scope of a constant is global.

Using define() function to define a constant

<?php
// Defining constant
define("WEBSITE", "http://www.lautturi.com");
 
echo 'Welcome to visit - ' . WEBSITE;
?>

A valid constant name starts with a letter or underscore, followed by any number of letters, numbers, or underscores.

// Invalid constant names
define("2FOO",    "something");

<?php
const HOST = 'Lautturi.com';

echo "Hello ".HOST;
?>

PHP provides some predefined constants,they are called "magical" constants.

Name	Description
LINE	The current line number of the file.
FILE	The full path and filename of the file with symlinks resolved. If used inside an include, the name of the included file is returned.
DIR	The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(FILE). This directory name does not have a trailing slash unless it is the root directory.
FUNCTION	The function name, or {closure} for anonymous functions.
CLASS	The class name. The class name includes the namespace it was declared in (e.g. Foo\Bar). Note that as of PHP 5.4 CLASS works also in traits. When used in a trait method, CLASS is the name of the class the trait is used in.
TRAIT	The trait name. The trait name includes the namespace it was declared in (e.g. Foo\Bar).
METHOD	The class method name.
NAMESPACE	The name of the current namespace.

ClassName::class The fully qualified class name. See also ::class.

<?php
    echo "The script file is:".__FILE__;
    echo PHP_EOL;
    echo "The current line number:".__LINE__;
?>

Output:

The script file is:D:\Apache24\htdocs\index.php
The current line number:4

Date：2019-10-01 01:06:25 From:www.Lautturi.com author：Lautturi