What's better of require(dirname(__FILE__).'/'.'myParent.php') than just require('myParent.php')?

PHP needs to know the absolute path to the file. dirname(__FILE__).'/myParent.php' already is the absolute path but 'myParent.php' requires a lookup using the given paths in include_path to get an absolute path and find the file. A better choice would be './myParent.php':

However, it is more efficient to explicitly use include './file' than having PHP always check the current directory for every include.

Besides the performance increase (which is likely a pre-optimization in most cases*), it also protects from the (very odd) scenario where the environment's PHP configuration does not have the current directory (.) as part of the include path.

* Benchmark of include using a path that requires include_path lookup versus a relative path that does not. Tested over 100000 iterations each

Results

include("include.php"):   8.3664200305939sinclude("./include.php"): 8.3511519432068s(8.3664200305939 - 8.3511519432068) / 100000 = 0.000000152680874s

Unless you're including hundreds or thousands of files, 0.0000001s is negligible at best.

Test code

define("MAX", 100000);ob_start();$i = MAX;$_t = microtime(true);do {    include("include.php");} while ( --$i );$_t = microtime(true) - $_t;ob_end_clean();echo "include(\"include.php\"):  {$_t}s\n";ob_start();$i = MAX;$_t = microtime(true);do {    include("./include.php");} while ( --$i );$_t = microtime(true) - $_t;ob_end_clean();

Test was conducted on a 2.16GHz Macbook 10.5.8 with PHP Version 5.2.9 (www.entropy.ch Release 7)

Using dirname + file name is slightly faster, because PHP will not iterate through include_path searching for the file. If speed matters, you will likely type more.