PHP Magic Constants: __FILE__, __DIR__, __LINE_

Magic constants are special built-in constants whose value depends on where in your code you use them. They start and end with two underscores.

Constant	Gives you
`__LINE__`	The current line number
`__FILE__`	The full path of the current file
`__DIR__`	The folder of the current file
`__FUNCTION__`	The name of the current function
`__CLASS__`	The name of the current class
`__METHOD__`	The class and method name
`__NAMESPACE__`	The current namespace

Example

index.php

PHP

<?php
function showWhere(): void
{
    echo "Function: " . __FUNCTION__ . "\n";
    echo "Line: " . __LINE__ . "\n";
}

showWhere();
echo "File name: " . basename(__FILE__);

Output

OUTPUT

1
2
3

Function: showWhere
Line: 5
File name: index.php

The one you will use most: DIR

When you include another file, a path like "config.php" depends on where the script was started. __DIR__ always gives a path that is relative to the current file, so it never breaks.

index.php

PHP

1
2

<?php
require __DIR__ . "/config.php";

You will use this a lot in Include and Require.

In classes

index.php

PHP

<?php
class Report
{
    public function title(): string
    {
        return __CLASS__ . " / " . __METHOD__;
    }
}

echo (new Report())->title();

Output

OUTPUT

Report / Report::title

lightbulb

Logging is a good use

A log message such as "Failed in " . __METHOD__ . " line " . __LINE__ tells you exactly where the problem happened.

Example

The one you will use most: __DIR__

In classes

Logging is a good use

The one you will use most: DIR