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Изрази> <Константи
Last updated: Fri, 27 Jun 2008

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Вълшебни константи

PHP предоставя голям брой предварително-дефинирани константи във всеки скрипт, който изпълнява. Много от тези константи, все пак, са създадени от различни разширения и ще бъдат налични единствено, в случай че тези разширения са налични, било то чрез динамично зареждане или защото са били компилирани.

Има пет вълшебни константи, които се променят според мястото, на което са използвани. Например, стойността на __LINE__ зависи от реда, на който се използва в скрипта ви. Тези специални константи не са чувствителни към регистъра и са както следва:

Няколко "вълшебни" PHP константи
Име Описание
__LINE__ Текущия номер на реда във файла.
__FILE__ Пълния път и име на файла. Ако се използва вътре във включен (include) файл, ще бъде върнато името на включвания файл. След PHP 4.0.2, __FILE__ винаги съдържа абсолютен път, докато в по-стари версии, при определени обстоятелства, съдържаше относителен път.
__DIR__ Директорията на файла. Ако се използва вътре във включен (include) файл, ще бъде върната директорията на включвания файл. Това е равносилно на dirname(__FILE__). Това име на директория няма последваща наклонена черта, освен ако не е коренната директория. (Добавена в PHP 5.3.0.)
__FUNCTION__ Името на функцията. (Това беше добавено в PHP 4.3.0) След PHP 5 тази константа връща името на функцията така, както е била дефинирана (чувствително към регистъра). В PHP 4 стойността й винаги е с малки букви.
__CLASS__ Името на класа. (Това беше добавено в PHP 4.3.0) След PHP 5 тази константа връща името на класа така, както е бил дефиниран (чувствително към регистъра). В PHP 4 стойността му винаги е с малки букви.
__METHOD__ Името на метода. (Това беше добавено в PHP 5.0.0) Връща името на метода така, както е бил дефиниран (чувствително към регистъра).
__NAMESPACE__ Името на текущото пространство от имена (чувствително към регистъра). Тази константа се дефинира по време на компилация (Добавена в PHP 5.3.0).

Вж. също get_class(), get_object_vars(), file_exists() и function_exists().



Изрази> <Константи
Last updated: Fri, 27 Jun 2008
 
add a note add a note User Contributed Notes
Вълшебни константи
me at jamessocol dot com
25-Jun-2008 06:11
We need an eighth magic constant, something along the lines of __STATIC__. This should return the name of the class from which a static method was called, regardless of where in the inheritance tree the method was defined.

PHP 5.3 has the new use of the static keyword which will help, but it isn't perfect. You still have to repeat yourself frequently.

For example, trying to implement Active Record:

<?php

// In PHP 5.3

class Model
{
    public static function find()
    {
        echo static::$class;
    }
}

class Product extends Model
{
    protected static $class = __CLASS__;
}

class User extends Model
{
    protected static $class = __CLASS__;
}

Product::find(); // "Product"
User::find(); // "User"

?>

<?php

// With __STATIC__ keyword. (Would be better.)

class Model
{
    public static function find()
    {
        echo __STATIC__;
    }
}

class Product extends Model {}

class User extends Model {}

Product::find(); // "Product"
User::find(); // "User"

?>
php at kennel17 dot co dot uk
20-Jun-2007 07:29
Further to my previous note, the 'object' element of the array can be used to get the parent object.  So changing the get_class_static() function to the following will make the code behave as expected:

<?php
    function get_class_static() {
        $bt = debug_backtrace();
   
        if (isset($bt[1]['object']))
            return get_class($bt[1]['object']);
        else
            return $bt[1]['class'];
    }
?>

HOWEVER, it still fails when being called statically.  Changing the last two lines of my previous example to

<?php
  foo::printClassName();
  bar::printClassName();
?>

...still gives the same problematic result in PHP5, but in this case the 'object' property is not set, so that technique is unavailable.
php at kennel17 dot co dot uk
20-Jun-2007 06:12
In response to stangelanda at gmail dot com, (who suggested a possible fix to get the actual class name of the object, when being called statically).

in PHP5, this fix no longer works. 

Here is some example code:

<?php

  function get_class_static() {
    $bt = debug_backtrace();
    $name = $bt[1]['class'];
    return $name;
  }

  class foo {
    function printClassName() {
      print(get_class_static() . "<br>");
     }
  }

  class bar extends foo {
  }

$f = new foo();
$b = new bar();
$f->printClassName();
$b->printClassName();

?>

In PHP4, it outputs
  foo
  bar
as you described.

However, in PHP5, due to the way the debug_backtrace() function has been modified (see http://bugs.php.net/bug.php?id=30828) the output is now
  foo
  foo

I have yet to figure out a way to get the original output in PHP5.  Any suggestions would be very useful, and if I find an answer I'll post it here.
Tomek Perlak [tomekperlak at tlen pl]
10-Nov-2006 11:16
The __CLASS__ magic constant nicely complements the get_class() function.

Sometimes you need to know both:
- name of the inherited class
- name of the class actually executed

Here's an example that shows the possible solution:

<?php

class base_class
{
    function say_a()
    {
        echo "'a' - said the " . __CLASS__ . "<br/>";
    }

    function say_b()
    {
        echo "'b' - said the " . get_class($this) . "<br/>";
    }

}

class derived_class extends base_class
{
    function say_a()
    {
        parent::say_a();
        echo "'a' - said the " . __CLASS__ . "<br/>";
    }

    function say_b()
    {
        parent::say_b();
        echo "'b' - said the " . get_class($this) . "<br/>";
    }
}

$obj_b = new derived_class();

$obj_b->say_a();
echo "<br/>";
$obj_b->say_b();

?>

The output should look roughly like this:

'a' - said the base_class
'a' - said the derived_class

'b' - said the derived_class
'b' - said the derived_class
stangelanda at gmail dot com
06-Sep-2006 06:17
claude noted that __CLASS__ always contains the class that it is called in, if you would rather have the class that called the method use get_class($this) instead.  However this only works with instances, not when called statically.

<?php
  class A {
     function showclass() {
         echo get_class($this);
     }
  }

  class B extends A {}

  $a = new A();
  $b = new B();

  $a->showclass();
  $b->showclass();
  A::showclass();
  B::showclass();

  //results in "a", "b", false, false
?>

I tried keeping track of the class manually within the properties, but the following doesn't work either:

<?php
  class A {
     var $class = __CLASS__;
     function showclass() {
         echo $this->class;
     }
  }

  class B extends A {
     var $class = __CLASS__;
  }

  //results in "a", "b", NULL, NULL
?>

The best solution I could come up with was using debug_backtrace.  I assume there is a better way somehow, but I can't find it.  However the following works:

<?php
  class A {
     function showclass() {
        $backtrace = debug_backtrace();
        echo $backtrace[0]['class'];
     }
  }

  class B extends A {}

  //results in "a", "b", "a", "b"
?>
warhog at warhog dot net
18-Dec-2005 10:33
There is another magic constant not mentioned above: __COMPILER_HALT_OFFSET__ - contains where the compiler halted - see http://www.php.net/manual/function.halt-compiler.php for further information.
vijaykoul_007 at rediffmail dot com
22-Sep-2005 06:59
the difference between
__FUNCTION__ and __METHOD__ as in PHP 5.0.4 is that

__FUNCTION__ returns only the name of the function

while as __METHOD__ returns the name of the class alongwith the name of the function

class trick
{
      function doit()
      {
                echo __FUNCTION__;
      }
      function doitagain()
      {
                echo __METHOD__;
      }
}
$obj=new trick();
$obj->doit();
output will be ----  doit
$obj->doitagain();
output will be ----- trick::doitagain
karl __at__ streetlampsoftware__dot__com
03-Mar-2005 10:39
Note that the magic constants cannot be included in quoted strings.

For instance,
echo "This is the filename: __FILE__";
will return exactly what's typed above.

echo "This is the filename: {__FILE__}";
will also return what's typed above.

The only way to get magic constants to parse in strings is to concatenate them into strings:
echo "This is the filename: ".__FILE__;
csaba at alum dot mit dot edu
03-Mar-2005 01:04
Sometimes you might want to know whether a script is the top level script or whether it has been included.  That could be useful if you want to reuse the routines in another script, but you don't want to separate them out.  Here's a way that seems to be working for me (for both Apache2 module and CLI versions of PHP) on my Win XP Pro system.

By the way, if __FILE__ is within a function call, its value corresponds to the file it was defined in and not the file that it was called from.  Also, I used $script and strtolower instead of realpath because if the script is deleted after inclusion but before realpath is called (which could happen if the test is deferred), then realpath would return empty since it requires an extant file or directory.

Csaba Gabor from Vienna

<?php
if (amIincluded()) return;    // if we're included we only want function defs
function amIincluded() {
//    returns true/false depending on whether the currently
//    executing script is included or not
//    Don't put this function in an include file (duh)!
    $webP = !!$_SERVER['REQUEST_METHOD'];    // a web request?
    $script = preg_replace('/\//',DIRECTORY_SEPARATOR,
                           $_SERVER['SCRIPT_FILENAME']);
    return ($webP) ? (strtolower(__FILE__)!=strtolower($script)) :
           !array_key_exists("_REQUEST", $GLOBALS);
}
?>
lm arobase bible point ch
08-Dec-2004 11:17
in reply to x123 at bestof dash inter:
I believe, this is not a bug, but a feature.
__FILE__ returns the name of the include file, while $PHP_SELF returns the relative name of the main file.
It is then easy to get the file name only with substr(strrchr($PHP_SELF,'/'),1)
claude at NOSPAM dot claude dot nl
18-Jul-2004 05:29
Note that __CLASS__ contains the class it is called in; in lowercase. So the code:

class A
{
    function showclass()
    {
        echo __CLASS__;
    }
}

class B extends A
{
}

$a = new A();
$b = new B();

$a->showclass();
$b->showclass();
A::showclass();
B::showclass();

results in "aaaa";
ulrik
04-Mar-2004 04:44
note that __FUNCTION__ define gives the the function name in lowercase
warhog at warhog dot net
06-Feb-2004 09:49
just to read out the filename of the currently proceeded file use
<?php basename(__FILE__); ?>
hixon at colorado dot edu
16-May-2003 02:21
You can use the following in files that you want to include, but not run directly.  The script will exit if it's run as the top-level script, but will not exit if it's included from another script.  Of course this won't work in the command line mode.

if (realpath(__FILE__) == realpath($_SERVER['SCRIPT_FILENAME'])) {
  exit;
}
kop at meme dot com
14-Feb-2003 12:34
The keywords TRUE and FALSE (case insensitive), which represent their respective boolean values, are worth noting here.
darwin[at]buchner[dot]net
15-Mar-2002 01:54
As of version 4.0.6, there is also a handy predefined DIRECTORY_SEPARATOR constant which you can use to make you scripts more portatable between OS's with different directory structures.
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Изрази> <Константи
Last updated: Fri, 27 Jun 2008
 
 
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