What's better of require(dirname(__FILE__).

问题:

Lots of famous PHP scripts including WordPress use dirname(__FILE__).'/myParent.php' instead of just 'myParent.php' when including files in the same directory of the currently running script.

Aren't they the same thing? Why do you prefer typing more?

Thanks.

回答1:

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.

回答2:

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"):   8.3664200305939s
include("./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)

回答3:

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.

回答4:

An added note about include('./file.php').

If only speed matters, then yes you can use include('./file.php'), but if you want to resolve dependencies and relative paths issues, you're better off using dirname(__ FILE __), because

include('./file.php')

will still construct paths relative to the executing script (the including script), while

include(dirname(__FILE__).'/file.php');

will resolve paths relative to the current script where this line resides (the included script).

Generally, you're better off using dirname(__ FILE __ ), since './' only gives a negligible performance increase while dirname(__ FILE __ ) gives you a lot more reliable include.

/EDIT: Also note that the benchmark done above only concerns include('./something.php'), which indeed is faster than include('something.php') because you don't have the include_path walking, but when you use dirname(__FILE__) you get the dirname() function call overhead, which makes it slower than walking the include_path (unless you have a lot paths in your include_path).