Best practices for usage of PHP’s Magic Constants

Question

What are the best practices for usage of PHP’s Magic Constants, such as __LINE__ , __FILE__, __FUNCTION__, __CLASS__ and __METHOD__?

For example I use __LINE__ and __CLASS__ to locate the SQL Error like this :

$result = mysql_query($query)
or die("Error SQL line ".__LINE__ ." class ".__CLASS__." : ".mysql_error());

Is this an acceptable practice?

Answer 1

The practice you show has two shortcomings:

• You are not showing the file the error occurs in - you'd have to have a very strict file structure that maps classes to files 1:1 for this to be useful

• __CLASS__ will show you the wrong result if the error occurs in an inherited class. Use get_class($this) to get the actual current class.

Other than that, using these constants is perfectly acceptable. Note that

• __FUNCTION__ and __CLASS__ were added in PHP 4.3

• __METHOD__ is available since PHP 5.0.0

• __DIR__ and __NAMESPACE__ are available since PHP 5.3.

docs

Answer 2

The purpose for these constants is debugging and logging. This is exactly what you are doing.

__FILE__ can also be used for relative file paths (e.g. dirname(__FILE__)).

Answer 3

The only advice I can give is that not all magic constants are defined. So, when in doubt, use if(defined('__MAGIC_CONSTANT__'))