Some interesting behavior (tested with PHP5), using the static-scope-keyword inside of class-methods.
<?php
class sample_class
{
public function func_having_static_var($x = NULL)
{
static $var = 0;
if ($x === NULL)
{ return $var; }
$var = $x;
}
}
$a = new sample_class();
$b = new sample_class();
echo $a->func_having_static_var()."\n";
echo $b->func_having_static_var()."\n";
// this will output (as expected):
// 0
// 0
$a->func_having_static_var(3);
echo $a->func_having_static_var()."\n";
echo $b->func_having_static_var()."\n";
// this will output:
// 3
// 3
// maybe you expected:
// 3
// 0
?>
One could expect "3 0" to be outputted, as you might think that $a->func_having_static_var(3); only alters the value of the static $var of the function "in" $a - but as the name says, these are class-methods. Having an object is just a collection of properties, the functions remain at the class. So if you declare a variable as static inside a function, it's static for the whole class and all of its instances, not for each object.
Maybe it's senseless to post that.. cause if you want to have the behaviour that I expected, you can simply use a variable of the object itself:
<?php
class sample_class
{ protected $var = 0;
function func($x = NULL)
{ $this->var = $x; }
} ?>
I believe that all normal-thinking people would never even try to make this work with the static-keyword, for those who try (like me), this note maybe helpfull.
Geltungsbereich von Variablen
Der Geltungsbereich einer Variablen ergibt sich aus dem Zusammenhang, in dem sie definiert wurde. Meistens besteht dieser aus einem einzigen Bereich. Dieser beinhaltet auch den Bereich für Dateien, die per "include"- oder "require"-Anweisung eingebunden wurden, z.B.:
<?php
$a = 1;
include 'b.inc';
?>
Die Variable $a ist auch in der eingebundenen Datei b.inc verfügbar. In benutzerdefinierten Funktionen wird jedoch ein auf die Funktion beschränkter Geltungsbereich eingeführt. Jede in einer Funktion benutzte Variable ist zunächst auf den lokalen Bereich der Funktion beschränkt, z.B.:
<?php
$a = 1; // globaler Geltungsbereich
function test () {
echo $a; // Referenz auf ein Variable im lokalen Geltungsbereich
}
test ();
?>
Dieses Skript erzeugt keine Bildschirm-Ausgabe, da sich die Echo- Anweisung auf eine lokale Variable namens $a bezieht, und dieser kein Wert im lokalen Geltungsbereich zugewiesen worden ist. Dies ist ein kleiner Unterschied zu C, wo globale Variablen auch in Funktionen vorhanden sind, es sei denn, sie werden durch eine funktionsinterne Definition überschrieben. Das kann zu Problemen führen, so dass in PHP global geltende Variablen innerhalb von Funktionen als solche deklariert werden müssen.
Das global Schlüsselwort
Zunächst ein Beispiel für die Verwendung von global:
Beispiel #1 Verwendung von global
<?php
$a = 1;
$b = 2;
function Sum()
{
global $a, $b;
$b = $a + $b;
}
Sum();
echo $b;
?>
Das obige Skript gibt 3 aus. Durch das Deklararieren der Variablen $a und $binnerhalb der Funktion als global, weisen alle Referenzen zu beiden Variablen auf die nun globalen Werte. Es gibt keine Beschränkungen bei der Anzahl an globalen Variablen, die durch eine Funktion verändert werden können.
Eine weitere Möglichkeit besteht in der Verwendung des speziellen $GLOBALS PHP-Array. Das obige Beispiel kann damit auch so geschrieben werden:
Beispiel #2 Verwendung von $GLOBALS statt global
<?php
$a = 1;
$b = 2;
function Sum()
{
$GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
}
Sum();
echo $b;
?>
Das $GLOBALS-Array ist ein assoziatives Array mit dem Bezeichner der globalen Variablen als Schlüssel und dem Inhalt dieser Variablen als Wert des Array-Elements. Beachten Sie, dass $GLOBALS in jedem Geltungsbereich existiert, weil $GLOBALS eine Superglobale ist. Hier ist ein Beispiel, das die Stärke von Superglobalen demonstriert:
Beispiel #3 Beispiel zur Demonstration von Superglobalen und Geltungsbereich
<?php
function test_superglobal()
{
echo $_POST['name'];
}
?>
Hinweis:
Die Verwendung des global-Schlüsselworts außerhalb einer Funktion ist kein Fehler. Es kann verwendet werden, wenn die Datei von innerhalb einer Funktion eingebunden wird.
Die Verwendung von static Variablen
Ein weiterer wichtiger Anwendungszweck von Variablen-Bereichen ist die statische-Variable. Eine statische Variable existiert nur in einem lokalen Funktions-Geltungsbereich, der Wert geht beim Verlassen dieses Bereichs aber nicht verloren. Schauen Sie das folgende Beispiel an:
Beispiel #4 Beispiel, das die Notwendigkeit von statischen Variablen demonstriert
<?php
function test ()
{
$a = 0;
echo $a;
$a++;
}
?>
Diese Funktion ist sinnlos, da sie bei jedem Aufruf $a auf 0 setzt und 0 ausgibt. Die Anweisung $a++, welche den Wert erhöht, ergibt hier keinen Sinn, da der Wert von $a beim Verlassen der Funktion verloren geht. Um eine sinnvolle Zählfunktion zu implementieren, die ihren aktuell gesetzten Wert nicht vergisst, müssen Sie die Variable $a als statisch deklarieren:
Beispiel #5 Beispiel zur Verwendung statischer Variablen
<?php
function test()
{
static $a = 0;
echo $a;
$a++;
}
?>
Nun wird $a nur beim ersten Aufruf der Funktion initialisiert, und jedes mal wenn die test()-Funktion aufgerufen wird, wird sie den Wert von $a ausgeben, und den Variablenwert erhöhen.
Statische Variablen ermöglichen auch einen Weg zum Umgang mit rekursiven Funktionen. Das sind Funktionen, die sich selbst aufrufen. Hierbei besteht die Gefahr, so genannte Endlos- Schleifen zu programmieren. Sie müssen also einen Weg vorsehen, diese Rekursion zu beenden. Die folgende einfache Funktion zählt rekursiv bis 10. Die statische Variable $count wird benutzt, um die Rekursion zu beenden:
Beispiel #6 Statische Variablen in rekursiven Funktionen
<?php
function test()
{
static $count = 0;
$count++;
echo $count;
if ($count < 10) {
test();
}
$count--;
}
?>
Hinweis:
Statische Variablen werden wie in oben stehenden Beispielen deklariert. Von PHP 5.6 an ist es möglich diesen Variablen Werte zuzuweisen, die das Ergebnis von Ausdrücken sind, aber es dürfen hier keine Funktion verwendet werden, was einen Parse-Fehler auslöst.
Beispiel #7 Statische Variablen deklarieren
<?php
function foo(){
static $int = 0; // korrekt
static $int = 1+2; // korrekt (von PHP 5.6 an)
static $int = sqrt(121); // falsch (da es eine Funktion ist)
$int++;
echo $int;
}
?>
Hinweis:
Statische Deklarationen werden zur Übersetzungszeit aufgelöst.
Referenzen bei global und static Variablen
PHP implementiert die static- und global-Modifikatoren für Variablen als Referenzen. Zum Beispiel erzeugt eine echte globale Variable, die mit der Anweisung global in den Funktions-Geltungsbereich importiert wurde, tatsächlich eine Referenz zur globalen Variable. Das kann zu einem unerwarteten Verhalten führen, auf das im folgenden Beispiel eingegangen wird:
function test_global_ref() {
global $obj;
$new = new stdclass;
$obj = &$new;
}
function test_global_noref() {
global $obj;
$new = new stdclass;
$obj = $new;
}
test_global_ref();
var_dump($obj);
test_global_noref();
var_dump($obj);
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
NULL
object(stdClass)#1 (0) {
}
Ein ähnliches Verhalten gilt auch für die Anweisung static. Referenzen werden nicht statisch gespeichert:
<?php
function &get_instance_ref() {
static $obj;
echo "Statisches Objekt: ";
var_dump($obj);
if (!isset($obj)) {
$new = new stdclass;
// Der statischen Variablen eine Referenz zuweisen
$obj = &$new;
}
if (!isset($obj->property)) {
$obj->property = 1;
} else {
$obj->property++;
}
return $obj;
}
function &get_instance_noref() {
static $obj;
echo "Statisches Objekt: ";
var_dump($obj);
if (!isset($obj)) {
$new = new stdclass;
// Der statischen Variablen ein Objekt zuweisen
$obj = $new;
}
if (!isset($obj->property)) {
$obj->property = 1;
} else {
$obj->property++;
}
return $obj;
}
$obj1 = get_instance_ref();
$still_obj1 = get_instance_ref();
echo "\n";
$obj2 = get_instance_noref();
$still_obj2 = get_instance_noref();
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
Statisches Objekt: NULL
Statisches Objekt: NULL
Statisches Objekt: NULL
Statisches Objekt: object(stdClass)#3 (1) {
["property"]=>
int(1)
}
Dieses Beispiel demonstriert, dass die Referenz, die einer statischen Variablen zugewiesen wird, beim zweiten Aufruf der Funktion &get_instance_ref() vergessen ist.
add a note
User Contributed Notes 47 notes
warhog at warhog dot net ¶
14 years ago
dodothedreamer at gmail dot com ¶
9 years ago
Note that unlike Java and C++, variables declared inside blocks such as loops or if's, will also be recognized and accessible outside of the block, so:
<?php
for($j=0; $j<3; $j++)
{
if($j == 1)
$a = 4;
}
echo $a;
?>
Would print 4.
HOSSEIN doesn't want spam at TAKI.IR ¶
10 years ago
Please note for using global variable in child functions:
This won't work correctly...
<?php
function foo(){
$f_a = 'a';
function bar(){
global $f_a;
echo '"f_a" in BAR is: ' . $f_a . '<br />'; // doesn't work, var is empty!
}
bar();
echo '"f_a" in FOO is: ' . $f_a . '<br />';
}
?>
This will...
<?php
function foo(){
global $f_a; // <- Notice to this
$f_a = 'a';
function bar(){
global $f_a;
echo '"f_a" in BAR is: ' . $f_a . '<br />'; // work!, var is 'a'
}
bar();
echo '"f_a" in FOO is: ' . $f_a . '<br />';
}
?>
larax at o2 dot pl ¶
14 years ago
About more complex situation using global variables..
Let's say we have two files:
a.php
<?php
function a() {
include("b.php");
}
a();
?>
b.php
<?php
$b = "something";
function b() {
global $b;
$b = "something new";
}
b();
echo $b;
?>
You could expect that this script will return "something new" but no, it will return "something". To make it working properly, you must add global keyword in $b definition, in above example it will be:
global $b;
$b = "something";
dexen dot devries at gmail dot com ¶
3 years ago
If you have a static variable in a method of a class, all DIRECT instances of that class share that one static variable.
However if you create a derived class, all DIRECT instances of that derived class will share one, but DISTINCT, copy of that static variable in method.
To put it the other way around, a static variable in a method is bound to a class (not to instance). Each subclass has own copy of that variable, to be shared among its instances.
To put it yet another way around, when you create a derived class, it 'seems to' create a copy of methods from the base class, and thusly create copy of the static variables in those methods.
Tested with PHP 7.0.16.
<?php
require 'libs.php';
require 'setup.php';
class Base {
function test($delta = 0) {
static $v = 0;
$v += $delta;
return $v;
}
}
class Derived extends Base {}
$base1 = new Base();
$base2 = new Base();
$derived1 = new Derived();
$derived2 = new Derived();
$base1->test(3);
$base2->test(4);
$derived1->test(5);
$derived2->test(6);
var_dump([ $base1->test(), $base2->test(), $derived1->test(), $derived2->test() ]);
# => array(4) { [0]=> int(7) [1]=> int(7) [2]=> int(11) [3]=> int(11) }
# $base1 and $base2 share one copy of static variable $v
# derived1 and $derived2 share another copy of static variable $v
andrew at planetubh dot com ¶
11 years ago
Took me longer than I expected to figure this out, and thought others might find it useful.
I created a function (safeinclude), which I use to include files; it does processing before the file is actually included (determine full path, check it exists, etc).
Problem: Because the include was occurring inside the function, all of the variables inside the included file were inheriting the variable scope of the function; since the included files may or may not require global variables that are declared else where, it creates a problem.
Most places (including here) seem to address this issue by something such as:
<?php
//declare this before include
global $myVar;
//or declare this inside the include file
$nowglobal = $GLOBALS['myVar'];
?>
But, to make this work in this situation (where a standard PHP file is included within a function, being called from another PHP script; where it is important to have access to whatever global variables there may be)... it is not practical to employ the above method for EVERY variable in every PHP file being included by 'safeinclude', nor is it practical to staticly name every possible variable in the "global $this" approach. (namely because the code is modulized, and 'safeinclude' is meant to be generic)
My solution: Thus, to make all my global variables available to the files included with my safeinclude function, I had to add the following code to my safeinclude function (before variables are used or file is included)
<?php
foreach ($GLOBALS as $key => $val) { global $$key; }
?>
Thus, complete code looks something like the following (very basic model):
<?php
function safeinclude($filename)
{
//This line takes all the global variables, and sets their scope within the function:
foreach ($GLOBALS as $key => $val) { global $$key; }
/* Pre-Processing here: validate filename input, determine full path
of file, check that file exists, etc. This is obviously not
necessary, but steps I found useful. */
if ($exists==true) { include("$file"); }
return $exists;
}
?>
In the above, 'exists' & 'file' are determined in the pre-processing. File is the full server path to the file, and exists is set to true if the file exists. This basic model can be expanded of course. In my own, I added additional optional parameters so that I can call safeinclude to see if a file exists without actually including it (to take advantage of my path/etc preprocessing, verses just calling the file exists function).
Pretty simple approach that I could not find anywhere online; only other approach I could find was using PHP's eval().
pogregoire##live.fr ¶
4 years ago
writing : global $var; is exactely the samething that writing : $var =& $GLOBALS['var'];
It creates a reference on $GLOBALS['var'];
<?php
$var =1;
function teste_global(){
global $var;
for ($var=0; $var<5; $var++){
}
}
teste_global();
var_dump($var);// return : int(5).
?>
Michael Bailey (jinxidoru at byu dot net) ¶
16 years ago
Static variables do not hold through inheritance. Let class A have a function Z with a static variable. Let class B extend class A in which function Z is not overwritten. Two static variables will be created, one for class A and one for class B.
Look at this example:
<?php
class A {
function Z() {
static $count = 0;
printf("%s: %d\n", get_class($this), ++$count);
}
}
class B extends A {}
$a = new A();
$b = new B();
$a->Z();
$a->Z();
$b->Z();
$a->Z();
?>
This code returns:
A: 1
A: 2
B: 1
A: 3
As you can see, class A and B are using different static variables even though the same function was being used.
ddarjany at yahoo dot com ¶
12 years ago
Note that if you declare a variable in a function, then set it as global in that function, its value will not be retained outside of that function. This was tripping me up for a while so I thought it would be worth noting.
<?PHP
foo();
echo $a; // echoes nothing
bar();
echo $b; //echoes "b";
function foo() {
$a = "a";
global $a;
}
function bar() {
global $b;
$b = "b";
}
?>
alan ¶
14 years ago
Using the global keyword inside a function to define a variable is essentially the same as passing the variable by reference as a parameter:
<?php
somefunction(){
global $var;
}
?>
is the same as:
<?php
somefunction(& $a) {
}
?>
The advantage to using the keyword is if you have a long list of variables needed by the function - you dont have to pass them every time you call the function.
zweibieren at yahoo dot com ¶
5 years ago
Take to heart this hard-won rule:
Declare AT THE TOP any variable that is to be global.
Both at the top of the FILE
AND at the top of any FUNCTION where it appears.
Why AT THE TOP? So it is sure to be declared before use. Otherwise a non-global version of the variable will be created and your code will fail.
Why at the top of a FUNCTION? Because otherwise the function will refer only to its local version of the variable and your code will fail.
Why at the top of the FILE? Because someday--a day that you cannot now imagine--you will want to "include" the file. And when you do, instances of the variable outside functions will not go in the global scope and your code will fail. (When the "include" is inside a calling function, variables in the included file go into the scope of the calling function.)
Example file where variable $x is used outside and inside functions:
|<!DOCTYPE html ...>
|<html xmlns ...>
| <?php global $x; ?>
|<head>
| Some html headers
| <?php
| $x = 1;
| function bump_x() {
| global $x;
| $x += 1;
| }
| ?>
|</head>
|<body>
| More html
| <?php echo $x; bump_x(); ?>
| Yet more html.
|</body>
</html>
Randolpho ¶
16 years ago
More on static variables:
A static variable does not retain it's value after the script's execution. Don't count on it being available from one page request to the next; you'll have to use a database for that.
Second, here's a good pattern to use for declaring a static variable based on some complex logic:
<?php
function buildStaticVariable()
{
$foo = null;
// some complex expression or set of
// expressions/statements to build
// the return variable.
return $foo;
}
function functionWhichUsesStaticVar()
{
static $foo = null;
if($foo === null) $foo = buildStaticVariable();
// the rest of your code goes here.
}
?>
Using such a pattern allows you to separate the code that creates your default static variable value from the function that uses it. Easier to maintain code is good. :)
tc underline at gmx TLD ch ¶
15 years ago
Pay attention while unsetting variables inside functions:
<?php
$a = "1234";
echo "<pre>";
echo "outer: $a\n";
function testa()
{
global $a;
echo " inner testa: $a\n";
unset ($a);
echo " inner testa: $a\n";
}
function testb()
{
global $a;
echo " inner testb: $a\n";
$a = null;
echo " inner testb: $a\n";
}
testa();
echo "outer: $a\n";
testb();
echo "outer: $a\n";
echo "</pre>";
?>
/***** Result:
outer: 1234
inner testa: 1234
inner testa:
outer: 1234
inner testb: 1234
inner testb:
outer:
******/
Took me 1 hour to find out why my variable was still there after unsetting it ...
Thomas Candrian
php at keith tyler dot com ¶
9 years ago
Sometimes a variable available in global scope is not accessible via the 'global' keyword or the $GLOBALS superglobal array. I have not been able to replicate it in original code, but it occurs when a script is run under PHPUnit.
PHPUnit provides a variable "$filename" that reflects the name of the file loaded on its command line. This is available in global scope, but not in object scope. For example, the following phpUnit script (call it GlobalScope.php):
<?php
print "Global scope FILENAME [$filename]\n";
class MyTestClass extends PHPUnit_Framework_TestCase {
function testMyTest() {
global $filename;
print "Method scope global FILENAME [$filename]\n";
print "Method scope GLOBALS[FILENAME] [".$GLOBALS["filename"]."]\n";
}
}
?>
If you run this script via "phpunit GlobalScope.php", you will get:
Global scope FILENAME [/home/ktyler/GlobalScope.php]
PHPUnit 3.4.5 by Sebastian Bergmann.
Method scope global FILENAME []
Method scope GLOBALS[FILENAME] []
.
You have to -- strange as it seems -- do the following:
<?php
$GLOBALS["filename"]=$filename;
print "Global scope FILENAME [$filename]\n";
class MyTestClass extends PHPUnit_Framework_TestCase {
function testMyTest() {
global $filename;
print "Method scope global FILENAME [$filename]\n";
print "Method scope GLOBALS[FILENAME] [".$GLOBALS["filename"]."]\n";
}
}
?>
By doing this, both "global" and $GLOBALS work!
I don't know what it is that PHPUnit does (I know it uses Reflection) that causes a globally available variable to be implicitly unavailable via "global" or $GLOBALS. But there it is.
eduardo dot ferron at zeion dot net ¶
10 years ago
There're times when global variables comes in handy, like universal read only resources you just need to create once in your application and share to the rest of your scripts. But it may become quite hard to track with "variables".
Jonathan Kenigson ¶
6 years ago
Just a note about static properties declared at class level:
class Test_Class {
static $a = 0;
public function ReturnVar(){
return $this->a;
}
}
$b = new Test_Class();
echo $b->ReturnVar();
Will not output "0" because $a is declared static. Changing "static" to "public" or "private" will produce the output "0".
Anonymous ¶
8 years ago
It will be obvious for most of you: changing value of a static in one instance changes value in all instances.
<?php
class example {
public static $s = 'unchanged';
public function set() {
$this::$s = 'changed';
}
}
$o = new example;
$p = new example;
$o->set();
print "$o static: {$o::$i}\n$p static: {$p::$i}";
?>
Output will be:
$o static: changed
$p static: changed
danno at wpi dot edu ¶
19 years ago
WARNING! If you create a local variable in a function and then within that function assign it to a global variable by reference the object will be destroyed when the function exits and the global var will contain NOTHING! This main sound obvious but it can be quite tricky you have a large script (like a phpgtk-based gui app ;-) ).
example:
<?php
function foo ()
{
global $testvar;
$localvar = new Object ();
$testvar = &$localvar;
}
foo ();
print_r ($testvar); // produces NOTHING!!!!
?>
hope this helps someone before they lose all their hair
kouber at php dot net ¶
15 years ago
If you need all your global variables available in a function, you can use this:
<?php
function foo() {
extract($GLOBALS);
// here you have all global variables
}
?>
gried at NOSPAM dot nsys dot by ¶
4 years ago
In fact all variables represent pointers that hold address of memory area with data that was assigned to this variable. When you assign some variable value by reference you in fact write address of source variable to recepient variable. Same happens when you declare some variable as global in function, it receives same address as global variable outside of function. If you consider forementioned explanation it's obvious that mixing usage of same variable declared with keyword global and via superglobal array at the same time is very bad idea. In some cases they can point to different memory areas, giving you headache. Consider code below:
<?php
error_reporting(E_ALL);
$GLOB = 0;
function test_references() {
global $GLOB; // get reference to global variable using keyword global, at this point local variable $GLOB points to same address as global variable $GLOB
$test = 1; // declare some local var
$GLOBALS['GLOB'] = &$test; // make global variable reference to this local variable using superglobal array, at this point global variable $GLOB points to new memory address, same as local variable $test
$GLOB = 2; // set new value to global variable via earlier set local representation, write to old address
echo "Value of global variable (via local representation set by keyword global): $GLOB <hr>";
// check global variable via local representation => 2 (OK, got value that was just written to it, cause old address was used to get value)
echo "Value of global variable (via superglobal array GLOBALS): $GLOBALS[GLOB] <hr>";
// check global variable using superglobal array => 1 (got value of local variable $test, new address was used)
echo "Value ol local variable \$test: $test <hr>";
// check local variable that was linked with global using superglobal array => 1 (its value was not affected)
global $GLOB; // update reference to global variable using keyword global, at this point we update address that held in local variable $GLOB and it gets same address as local variable $test
echo "Value of global variable (via updated local representation set by keyword global): $GLOB <hr>";
// check global variable via local representation => 1 (also value of local variable $test, new address was used)
}
test_references();
echo "Value of global variable outside of function: $GLOB <hr>";
// check global variable outside function => 1 (equal to value of local variable $test from function, global variable also points to new address)
?>
moraesdno at gmail dot com ¶
11 years ago
Use the superglobal array $GLOBALS is faster than the global keyword. See:
<?php
//Using the keyword global
$a=1;
$b=2;
function sum() {
global $a, $b;
$a += $b;
}
$t = microtime(true);
for($i=0; $i<1000; $i++) {
sum();
}
echo microtime(true)-$t;
echo " -- ".$a."<br>";
//Using the superglobal array
$a=1;
$b=2;
function sum2() {
$GLOBALS['a'] += $GLOBALS['b'];
}
$t = microtime(true);
for($i=0; $i<1000; $i++) {
sum2();
}
echo microtime(true)-$t;
echo " -- ".$a."<br>";
?>
simon dot barotte at gmail dot com ¶
3 years ago
To be vigilant, unlike Java or C++, variables declared inside blocks such as loops (for, while,...) or if's, will also be recognized and accessible outside of the block, the only valid block is the BLOCK function so:
<?php
for($j=0; $j<5; $j++)
{
if($j == 1){
$a = 6;
}
}
echo $a;
?>
Would print 6.
jakub dot lopuszanski at nasza-klasa dot pl ¶
10 years ago
If you use __autoload function to load classes' definitons, beware that "static local variables are resolved at compile time" (whatever it really means) and the order in which autoloads occur may impact the semantic.
For example if you have:
<?php
class Singleton{
static public function get_instance(){
static $instance = null;
if($instance === null){
$instance = new static();
}
return $instance;
}
}
?>
and two separate files A.php and B.php:
class A extends Singleton{}
class B extends A{}
then depending on the order in which you access those two classes, and consequently, the order in which __autoload includes them, you can get strange results of calling B::get_instance() and A::get_instance().
It seems that static local variables are alocated in as many copies as there are classes that inherit a method at the time of inclusion of parsing Singleton.
Stephen Dewey ¶
11 years ago
For nested functions:
This is probably obvious to most people, but global always refers to the variable in the global (top level) variable of that name, not just a variable in a higher-level scope. So this will not work:
<?php
// $var1 is not declared in the global scope
function a($var1){
function b(){
global $var1;
echo $var1; // there is no var1 in the global scope so nothing to echo
}
b();
}
a('hello');
?>
Anonymous ¶
12 years ago
I was pondering a little something regarding caching classes within a function in order to prevent the need to initiate them multiple times and not clutter the caching function's class properties with more values.
I came here because I remembered something about references being lost. So I made a test to see if I could pull what I wanted to off anyway. Here's and example of how to get around the references lost issue. I hope it is helpful to someone else!
<?php
class test1{}
class test2{}
class test3{}
function cache( $class )
{
static $loaders = array();
$loaders[ $class ] = new $class();
var_dump( $loaders );
}
print '<pre>';
cache( 'test1' );
cache( 'test2' );
cache( 'test3' );
?>
info AT SyPlex DOT net ¶
16 years ago
Some times you need to access the same static in more than one function. There is an easy way to solve this problem:
<?php
// We need a way to get a reference of our static
function &getStatic() {
static $staticVar;
return $staticVar;
}
// Now we can access the static in any method by using it's reference
function fooCount() {
$ref2static = & getStatic();
echo $ref2static++;
}
fooCount(); // 0
fooCount(); // 1
fooCount(); // 2
?>
jameslee at cs dot nmt dot edu ¶
15 years ago
It should be noted that a static variable inside a method is static across all instances of that class, i.e., all objects of that class share the same static variable. For example the code:
<?php
class test {
function z() {
static $n = 0;
$n++;
return $n;
}
}
$a =& new test();
$b =& new test();
print $a->z(); // prints 1, as it should
print $b->z(); // prints 2 because $a and $b have the same $n
?>
somewhat unexpectedly prints:
1
2
jake dot tunaley at berkeleyit dot com ¶
1 year ago
Beware of using $this in anonymous functions assigned to a static variable.
<?php
class Foo {
public function bar() {
static $anonymous = null;
if ($anonymous === null) {
// Expression is not allowed as static initializer workaround
$anonymous = function () {
return $this;
};
}
return $anonymous();
}
}
$a = new Foo();
$b = new Foo();
var_dump($a->bar() === $a); // True
var_dump($b->bar() === $a); // Also true
?>
In a static anonymous function, $this will be the value of whatever object instance that method was called on first.
To get the behaviour you're probably expecting, you need to pass the $this context into the function.
<?php
class Foo {
public function bar() {
static $anonymous = null;
if ($anonymous === null) {
// Expression is not allowed as static initializer workaround
$anonymous = function (self $thisObj) {
return $thisObj;
};
}
return $anonymous($this);
}
}
$a = new Foo();
$b = new Foo();
var_dump($a->bar() === $a); // True
var_dump($b->bar() === $a); // False
?>
Hayley Watson ¶
2 years ago
static variables are implicitly initialised to NULL if no explicit initialisation is made.
<?php
function foo()
{
static $v;
echo gettype($v);
}
foo();
?>
will echo NULL without complaining that $v is undefined.
In short: "static $v;" is equivalent to "static $v = null;".
Semyon Naitur ¶
3 years ago
function f(){
global $a; // global $a is declared, local reference is created
$a = 'a'; // global $a is set
unset($a); // local reference is unset, global $a remains set
$a = 'b'; // local $a is declared and set
}
f();
echo $a; // prints 'a'
function f(){
global $a; // global $a is declared, local reference is created
$a = 'a'; // global $a is set
unset($a); // local reference $a is unset, global var $a remains set
global $a; // local reference is created again
$a .= 'b';
}
f();
echo $a; // prints 'ab'
Ganlv ¶
4 years ago
<?php
$var = 1;
function foo() {
$var = &$GLOBALS['var'];
var_dump($var);
}
function bar() {
global $var; // they are the same.
var_dump($var);
}
foo();
bar();
var_dump($var);
?>
In a function, 'global $var;' is to declare a local variant, and the local $var has the same reference to the global $var.
<?php
$var = 1;
function foo() {
global $var;
unset($var); // unset local $a, the global $a is still there.
var_dump($var); // Undefined variable: var
var_dump($GLOBALS['var']); // this is ok.
}
foo();
var_dump($var); // this is ok.
?>
<?php
$var = 1;
function bar() {
global $var;
unset($GLOBALS['var']); // unset global $a, the local $a is still here.
var_dump($var); // this is ok.
var_dump($GLOBALS['var']); // Undefined index: var
}
foo();
var_dump($var); // Undefined variable: var
?>
'unset($var);' is like 'var = NULL;'(var is a pointer) in the C language, instead of 'free(var);'
nino dot skopac at gmail dot com ¶
5 years ago
Interesting behavior in PHP 5.6.12 and PHP 7 RC3:
<?php
class Foo {
public function Bar() {
static $var = 0;
return ++$var;
}
}
$Foo_instance = new Foo;
print $Foo_instance->Bar(); // prints 1
print PHP_EOL;
unset($Foo_instance);
$Foo_instance2 = new Foo;
print $Foo_instance2->Bar(); // prints 2
print PHP_EOL;
?>
How can a 2 be printed, since we unseted the whole instance before?
Consider a similar example:
<?php
class Foo {
public static $var = 0;
public static function Bar() {
return ++self::$var;
}
}
$Foo_instance = new Foo;
print $Foo_instance->Bar(); // prints 1
print PHP_EOL;
unset($Foo_instance);
$Foo_instance2 = new Foo;
print $Foo_instance2->Bar(); // prints 2
print PHP_EOL;
?>
No idea why is this happening.
Ray.Paseur often uses Gmail ¶
6 years ago
Variable "Visibility" in PHP Object Oriented Programming is documented here:
http://php.net/manual/en/language.oop5.visibility.php
pedro at worcel dot com ¶
10 years ago
Another way of working with a large ammount of global variables could be the following.
<?php
$var = "3";
$smarty = new Smarty();
function headers_set_404() {
extract($globals);
echo $var . "<br />";
print_r($smarty);
return;
}
?>
Regards,
Droope
nullhility at gmail dot com ¶
11 years ago
Like functions, if you declare a variable in a class, then set it as global in that class, its value will not be retained outside of that class either.
<?php
class global_reference
{
public $val;
public function __construct () {
global $var;
$this->val = $var;
}
public function dump_it ()
{
debug_zval_dump($this->val);
}
public function type_cast ()
{
$this->val = (int) $this->val;
}
}
$var = "x";
$obj = new global_reference();
$obj->dump_it();
$obj->type_cast();
echo "after change ";
$obj->dump_it();
echo "original $var\n";
?>
The work-around is of course changing the assignment in the constructor to a reference assignment as such:
<?php
//....
$this->val = &var;
//....
?>
If the global you're setting is an object then no reference is necessary because of the way PHP deals with objects. If you don't want to reference to the same object however you can use the clone keyword.
<?php
//...
global $Obj;
$this->obj_copy = clone $Obj;
//...
?>
[EDIT BY danbrown AT php DOT net: Merged all thoughts and notes by this author into a single note.]
franp at free dot fr ¶
14 years ago
If you want to access a table row using $GLOBALS, you must do it outside string delimiters or using curl braces :
<?php
$siteParams["siteName"] = "myweb";
function foo() {
$table = $GLOBALS["siteParams"]["siteName"]."articles"; // OK
echo $table; // output "mywebarticles"
$table = "{$GLOBALS["siteParams"]["siteName"]}articles"; // OK
echo $table; // output "mywebarticles"
$table = "$GLOBALS[siteParams][siteName]articles"; // Not OK
echo $table; // output "Array[siteName]article"
$result = mysql_query("UPDATE $table ...");
}
?>
Or use global :
<?php
function foo() {
global $siteParams;
$table = "$siteParams[siteName]articles"; // OK
echo $table; // output "mywebarticles"
$result = mysql_query("UPDATE $table ...");
}
?>
heatwave at fw dot hu ¶
18 years ago
Some people (including me) had a problem with defining a long GLOBAL variable list in functions (very error prone). Here is a possible solution. My program parses php file for functions, and compiles GLOBAL variable lists. Then you can just remove from the list those variables which need not be global.
<?php
//parser for GLOBAL variable list
$pfile=file("myfile.php4");
for($i=0;$i<sizeof($pfile);$i++) {
if(eregi("function",$pfile[$i])) {
list($part1,$part2)=sscanf($pfile[$i],"%s %s");
echo "\n\n $part1 $part2:\nGLOBAL ";
$varlist=array();
$level=0; $end=$i;
do {
$lpar=explode("{",$pfile[$end]);
$level+=sizeof($lpar)-1;
$lpar=explode("}",$pfile[$end]);
$level-=sizeof($lpar)-1;
$end++;
} while(($end<sizeof($pfile))&&($level>0));
$pstr="";
for($j=$i;$j<=$end;$j++) $pstr.=$pfile[$j];
$lpar=explode("$",$pstr);
for($j=1;$j<sizeof($lpar);$j++) {
eregi('[a-zA-Z_][a-zA-Z0-9_]*',$lpar[$j],$cvar);
$varlist[$cvar[0]]=1;
}
array_walk($varlist,'var_print');
}
}
function var_print ($item, $key) {
echo "$key,";
}
?>
admin at essentialhost dot com ¶
18 years ago
Quick tip for beginners just to speed things up:
If you have a bunch of global variables to import into a function, it's best to put them into a named array like $variables[stuff].
When it's time to import them you just so the following;
<?php
function here() {
$vars = $GLOBALS['variables'];
print $vars[stuff];
}
?>
This really helps with big ugly form submissions.
sami doesn't want spam at no-eff-eks com ¶
14 years ago
PHP 5.1.4 doesn't seem to care about the static keyword. It doesn't let you use $this in a static method, but you can call class methods through an instance of the class using regular -> notation. You can also call instance methods as class methods through the class itself. The documentiation here is plain wrong.
<?php
class Foo {
public static function static_fun()
{
return "This is a class method!\n";
}
public function not_static_fun()
{
return "This is an instance method!\n";
}
}
echo '<pre>';
echo "From Foo:\n";
echo Foo::static_fun();
echo Foo::not_static_fun();
echo "\n";
echo "From \$foo = new Foo():\n";
$foo = new Foo();
echo $foo->static_fun();
echo $foo->not_static_fun();
echo '</pre>';
?>
You'll see the following output:
From Foo:
This is a class method!
This is an instance method!
From $foo = new Foo():
This is a class method!
This is an instance method!
emartin at sigb dot net ¶
11 years ago
If you are used to include files which declare global variables, and if you now need to include these files in a function, you will see that those globals are declared in the function's scope and so they will be lost at the end of the function.
You may use something like this to solve this problem:
main_file.php :
<?php
//Some innocent variables which exist before the problem
$a = 42;
$b = 33;
$c = 56;
function some_function() {
//Some variables that we don't want out of the function
$saucisse = "saucisse";
$jambon = "jambon";
//Let's include another file
$evalt = "require_once 'anothertest_include.php';";
$before_eval_vars = get_defined_vars();
eval($evalt);
//Let's extract the variables that were defined AFTER the call to 'eval'
$function_variable_names = array("function_variable_names" => 0, "before_eval_vars" => 0, "created" => 0);
//We can generate a list of the newly created variables by substracting the list of the variables of the function and the list of the variables which existed before the call to the list of current variables at this point
$created = array_diff_key(get_defined_vars(), $GLOBALS, $function_variable_names, $before_eval_vars);
//Now we globalize them
foreach ($created as $created_name => $on_sen_fiche)
global $$created_name;
//And we affect them
extract($created);
}
some_function();
print_r(get_defined_vars());
?>
included_file.php :
<?php
//Some variables that we want in the global scope of main_file.php
$included_var_one = 123;
$included_var_two = 465;
$included_var_three = 789;
?>
thomas at pixtur dot de ¶
15 years ago
Be careful with "require", "require_once" and "include" inside functions. Even if the included file seems to define global variables, they might not be defined as such.
consider those two files:
---index.php------------------------------
<?php
function foo() {
require_once("class_person.inc");
$person= new Person();
echo $person->my_flag; // should be true, but is undefined
}
foo();
?>
---class_person.inc----------------------------
<?php
$seems_global=true;
class Person {
public $my_flag;
public function __construct() {
global $seems_global;
$my_flag= $seems_global
}
}
?>
---------------------------------
The reason for this behavior is quiet obvious, once you figured it out. Sadly this might not be always as easy as in this example. A solution would be to add the line...
<?php global $seems_global; ?>
at the beginning of "class_person.inc". That makes sure you set the global-var.
best regards
tom
ps: bug search time approx. 1 hour.
Anonymous ¶
7 years ago
<?php
// if you really want to create a variable within its own scope
// that does not have access to variables outside its scope create a function
$var = "hello";
$func = function(){
// declare variables here that will only last throughout this scope
if( !isset($var) ) // var will not be set in this scope
{
$var = "i was out of scope";
}
echo $var;
};
echo "$var<br />";
$func(); // invoke the function
echo "<br />".'$var'." never changed from $var";
?>
outputs :
hello
i was out of scope
$var never changed from hello
wjs@sympaticoDOTca ¶
17 years ago
Becareful where you define your global variables:
This will work:
<?php
$MyArray = array("Dog");
function SeeArray(){
global $MyArray;
if (in_array("Dog",$MyArray)){
foreach ($MyArray as $Element){
echo "$Element <hr/>";
}
}
}
SeeArray();
?>
while this will not:
<?php
SeeArray();
$MyArray = array("Dog");
function SeeArray(){
global $MyArray;
if (in_array("Dog",$MyArray)){ // an error will generate here
foreach ($MyArray as $Element){
echo "$Element <hr/>";
}
}
}
?>
flobee at gmx dot net ¶
16 years ago
i found out that on any (still not found) reason the <?php static $val =NULL; ?> is not working when trying to extract the data form the $var with a while statment
e.g.:
<?php
funktion get_data() {
static $myarray = null;
if($myarray == NULL) {
//get some info in an array();
$myarray = array('one','two');
}
while(list($key,$val) = each( $myarray ) ) {
// do something
echo "x: $key , y: $val";
}
}
?>
when using foreach($myarray AS $key => $val) { .... instad of while then i see the result!
carpathia_uk at mail dot com ¶
19 years ago
On confusing aspect about global scope...
If you want to access a variable such as a cookie inside a function, but theres a chance it may not even be defined, you need to access it using he GLOBALS array, not by defining it as global.
This wont work correctly....
<?php
function isLoggedin()
{
global $cookie_username;
if (isset($cookie_username)
echo "blah..";
}
?>
This will..
<?php
function isLoggedin()
{
if (isset($GLOBALS["cookie_username"]))
echo "blah..";
}
?>
jordan at brownboots dot com ¶
2 years ago
Using $GLOBALS inside a function you can override all references to global variables in that function with variables passed into the function as arguments. This is useful when a function does stuff to a global object but you sometimes want it to do that stuff to a different object, and you don't want to rewrite any code.
For example, suppose there's a global object called $user that refers to the currently-logged-in user and a function that does stuff to that user object:
<?php
function example_function() {
global $user;
// do stuff with the object
echo $user->id;
}
?>
Here's how you can make that function optionally do stuff to a different user object:
<?php
function example_function(&$user = null) {
if(!isset($user)) { // if the function argument isn't provided, ...
$user = $GLOBALS['user']; // ... use the global variable
}
// do stuff with the object
echo $user->id;
}
?>
Example usage:
<?php
example_function(); // this will print the logged-in user's ID
$test_user = load_user_by_id(1453);
example_function($test_user); // this will print 1453
?>
Jack at soinsincere dot com ¶
16 years ago
Alright, so you can't set a static variable with a reference.
However, you can set a static variable to an array with an element that is a reference:
<?php
class myReference {
function getOrSet($array = null) {
static $myValue;
if (!$array) {
return $myValue[0]; //Return reference in array
}
$myValue = $array; //Set static variable with array
static $myValue;
}
}
$static = "Dummy";
$dummy = new myReference;
$dummy->getOrSet(array(&$static));
$static = "Test";
print $dummy->getOrSet();
?>
