PHP Australia Conference 2015

Ámbito de las variables

El ámbito de una variable es el contexto dentro del que la variable está definida. La mayor parte de las variables PHP sólo tienen un ámbito simple. Este ámbito simple también abarca los ficheros incluídos y los requeridos. Por ejemplo:

<?php
$a 
1;
include 
'b.inc';
?>

Aquí, la variable $a estará disponible al interior del script incluido b.inc. Sin embargo, al interior de las funciones definidas por el usuario se introduce un ámbito local a la función. Cualquier variable usada dentro de una función está, por omisión, limitada al ámbito local de la función. Por ejemplo:

<?php
$a 
1/* ámbito global */

function test()
{
    echo 
$a/* referencia a una variable del ámbito local */
}

test();
?>

Este script no producirá salida, ya que la sentencia echo utiliza una versión local de la variable $a, a la que no se ha asignado ningún valor en su ámbito. Puede que usted note que hay una pequeña diferencia con el lenguaje C, en el que las variables globales están disponibles automáticamente dentro de la función a menos que sean expresamente sobreescritas por una definición local. Esto puede causar algunos problemas, ya que la gente puede cambiar variables globales inadvertidamente. En PHP, las variables globales deben ser declaradas globales dentro de la función si van a ser utilizadas dentro de dicha función.

La palabra clave global

En primer lugar, un ejemplo de uso de global:

Ejemplo #1 Uso de global

<?php
$a 
1;
$b 2;

function 
Suma()
{
    global 
$a$b;

    
$b $a $b;
}

Suma();
echo 
$b;
?>

El script anterior producirá la salida 3. Al declarar $a y $b globales dentro de la función, todas las referencias a tales variables se referirán a la versión global. No hay límite al número de variables globales que se pueden manipular dentro de una función.

Un segundo método para acceder a las variables desde un ámbito global es usando el array $GLOBALS. El ejemplo anterior se puede reescribir así:

Ejemplo #2 Uso de $GLOBALS en lugar de global

<?php
$a 
1;
$b 2;

function 
Suma()
{
    
$GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
}

Suma();
echo 
$b;
?>

El array $GLOBALS es un array asociativo con el nombre de la variable global como clave y los contenidos de dicha variable como el valor del elemento del array. $GLOBALS existe en cualquier ámbito, esto ocurre ya que $GLOBALS es una superglobal. Aquí hay un ejemplo que demuestra el poder de las superglobales:

Ejemplo #3 Ejemplo que demuestra las superglobales y el ámbito

<?php
function test_global()
{
    
// La mayoría de variables predefinidas no son "super" y requieren
    // 'global' para estar disponibles al ámbito local de las funciones.
    
global $HTTP_POST_VARS;

    echo 
$HTTP_POST_VARS['name'];

    
// Las superglobales están disponibles en cualquier ámbito y no
    // requieren 'global'. Las superglobales están disponibles desde
    // PHP 4.1.0, y ahora HTTP_POST_VARS se considera obsoleta.
    
echo $_POST['name'];
}
?>

Nota:

Utilizar una clave global fuera de una función no es un error. Esta puede ser utilizada aún si el fichero está incluido desde el interior de una función.

Uso de variables static

Otra característica importante del ámbito de las variables es la variable estática. Una variable estática existe sólo en el ámbito local de la función, pero no pierde su valor cuando la ejecución del programa abandona este ámbito. Consideremos el siguiente ejemplo:

Ejemplo #4 Ejemplo que demuestra la necesidad de variables estáticas

<?php
function test()
{
    
$a 0;
    echo 
$a;
    
$a++;
}
?>

Esta función tiene poca utilidad ya que cada vez que es llamada asigna a $a el valor 0 e imprime un 0. La sentencia $a++, que incrementa la variable, no sirve para nada, ya que en cuanto la función finaliza, la variable $a desaparece. Para hacer una función útil para contar, que no pierda la pista del valor actual del conteo, la variable $a debe declararse como estática:

Ejemplo #5 Ejemplo del uso de variables estáticas

<?php
function test()
{
    static 
$a 0;
    echo 
$a;
    
$a++;
}
?>

Ahora, $a se inicializa únicamente en la primera llamada a la función, y cada vez que la función test() es llamada, imprimirá el valor de $a y lo incrementa.

Las variables estáticas también proporcionan una forma de manejar funciones recursivas. Una función recursiva es la que se llama a sí misma. Se debe tener cuidado al escribir una función recursiva, ya que puede ocurrir que se llame a sí misma indefinidamente. Hay que asegurarse de implementar una forma adecuada de terminar la recursión. La siguiente función cuenta recursivamente hasta 10, usando la variable estática $count para saber cuándo parar:

Ejemplo #6 Variables estáticas con funciones recursivas

<?php
function test()
{
    static 
$count 0;

    
$count++;
    echo 
$count;
    if (
$count 10) {
        
test();
    }
    
$count--;
}
?>

Nota:

Las variables estáticas pueden ser declaradas como se ha visto en los ejemplos anteriores. Al tratar de asignar valores a estas variables que sean el resultado de expresiones, causará un error de análisis sintáctico.

Ejemplo #7 Declaración de variables estáticas

<?php
function foo(){
    static 
$int 0;          // correcto
    
static $int 1+2;        // incorrecto  (ya que es una expresión)
    
static $int sqrt(121);  // incorrecto  (es una expresión también)

    
$int++;
    echo 
$int;
}
?>

Nota:

Las declaraciones estáticas son resueltas en tiempo de compilación.

Referencias con variables global y static

El motor Zend 1, utilizado por PHP 4, implementa los modificadores static y global para variables en términos de referencias. Por ejemplo, una variable global verdadera importada dentro del ámbito de una función con global crea una referencia a la variable global. Esto puede ser causa de un comportamiento inesperado, tal y como podemos comprobar en el siguiente ejemplo:

<?php
function prueba_referencia_global() {
    global 
$obj;
    
$obj = &new stdclass;
}

function 
prueba_no_referencia_global() {
    global 
$obj;
    
$obj = new stdclass;
}

prueba_referencia_global();
var_dump($obj);
prueba_no_referencia_global();
var_dump($obj);
?>

El resultado del ejemplo sería:


NULL
object(stdClass)(0) {
}

Un comportamiento similar se aplica a static. Las referencias no son almacenadas estáticamente.

<?php
function &obtener_instancia_ref() {
    static 
$obj;

    echo 
'Objeto estático: ';
    
var_dump($obj);
    if (!isset(
$obj)) {
        
// Asignar una referencia a la variable estática
        
$obj = &new stdclass;
    }
    
$obj->property++;
    return 
$obj;
}

function &
obtener_instancia_no_ref() {
    static 
$obj;

    echo 
'Objeto estático: ';
    
var_dump($obj);
    if (!isset(
$obj)) {
        
// Asignar el objeto a la variable estática
        
$obj = new stdclass;
    }
    
$obj->property++;
    return 
$obj;
}

$obj1 obtener_instancia_ref();
$aun_obj1 obtener_instancia_ref();
echo 
"\n";
$obj2 obtener_instancia_no_ref();
$aun_obj2 obtener_instancia_no_ref();
?>

El resultado del ejemplo sería:


Objeto estático: NULL
Objeto estático: NULL

Objeto estático: NULL
Objeto estático: object(stdClass)(1) {
["property"]=>
int(1)
}

Este ejemplo demuestra que al asignar una referencia a una variable estática, esta no es recordada cuando se invoca la funcion &obtener_instancia_ref() por segunda vez.

add a note add a note

User Contributed Notes 60 notes

up
29
warhog at warhog dot net
8 years ago
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.
up
13
HOSSEIN doesn&#39;t want spam at TAKI.IR
4 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 />';
}
?>
up
9
Stephen Dewey
5 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');

?>
up
6
jakub dot lopuszanski at nasza-klasa dot pl
4 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.
up
4
ddarjany at yahoo dot com
6 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";
}

?>
up
6
Anonymous
6 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' );

?>
up
5
php at keith tyler dot com
3 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.
up
3
Leigh Harrison
5 years ago
External variables in a function

I needed to access dynamically-created variables from an included file within a helper function. Because the list of $path_* variables I needed to access from the other file is itself dynamic, I didn't want to have to declare all possible variables within the function, and I was concerned at the overhead of declaring =all= members of $GLOBALS[] as global. However the following code worked for me:

<?php
 
function makePath($root, $atom) {
   
$pos = strrpos($atom, '/');
    if (
$pos === false) {
      global ${
'path_'.$atom}; 
     
$path = ${'path_'.$atom};
    }
    else {
      global ${
'path_'.substr($atom, 0, $pos)};
     
$path = ${'path_'.substr($atom, 0, $pos)};
    }
    if (
$path)
      return (
$pos === false)
        ?
$root.$path
       
: $root.$path.substr($atom, $pos + 1);
    else
      return
NULL;
  }
?>

Regards,

::Leigh
up
1
Jonathan Kenigson
9 months 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".
up
2
danno at wpi dot edu
13 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
up
3
andrew at planetubh dot com
5 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().
up
1
marcin
8 years ago
Sometimes in PHP 4 you need static variabiles in class. You can do it by referencing static variable in constructor to the class variable:

<?php
class test  {

   var
$var;
   var
$static_var;
    function
test()
    {
        static
$s;
       
$this->static_var =& $s;
    }
 
}

$a=new test();

$a->static_var=4;
$a->var=4;

$b=new test();

echo
$b->static_var; //this will output 4
echo $b->var; //this will output nul
?>
up
1
admin at essentialhost dot com
12 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.
up
3
dodothedreamer at gmail dot com
3 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.
up
1
eduardo dot ferron at zeion dot net
3 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".
up
1
pedro at worcel dot com
4 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
up
2
Anonymous
2 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
up
1
tc underline at gmx TLD ch
9 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
up
1
moraesdno at gmail dot com
4 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>";
?>
up
1
nullhility at gmail dot com
5 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.]
up
0
akam at akameng dot com
5 years ago
Many Times Globality of variables will be the small issue, after long time I decided to use super globals.

Super globals exists any where:
$_SERVER, $_GET, $_POST .....

Now for example:

<?php
$foo
[] = range(0, 3);
$_POST['foo'] = $foo;
a(); //no parameters needed.
b();
$foo = $_POST['foo'];

Print_r($foo);
/* out

Array
(
    [0] => Array
        (
            [0] => 0
            [1] => 1
            [2] => 2
            [3] => 3
        )

    [1] => Array
        (
            [0] => 4
            [1] => 5
            [2] => 6
            [3] => 7
        )

    [2] => Array
        (
            [0] => 8
            [1] => 9
            [2] => 10
        )

)

*/
function a(){
   
$_POST['foo'][] = range(4, 7);
}

function
b(){
$_POST['foo'][] = range(8, 10);
}
?>
Note: the key must not be passed by the page via _POST method by the form, else the value will be over written
up
-1
Tomas Binek
11 months ago
Be careful when using autoloaders:
Any variables that are declared in autoloaded files in global context are in fact local variables to the autoload function.
Suggestion:
Use explicit global keyword even in global context of a file.
up
-1
Anonymous
1 year 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
$var never changed from hello
up
0
lgrk
6 years ago
Useful function:
<?php
function cycle($a, $b, $i=0) {
    static
$switches = array();
    if (isset(
$switches[$i])) $switches[$i] = !$switches[$i]; else !$switches[$i] = true;
    return (
$switches[$i])?$a:$b;
}
?>

Exeample

<?php
for ($i = 1; $i<3; $i++) {
    echo
$i.cycle('a', 'b').PHP_EOL;
    for (
$j = 1; $j<5; $j++) {
        echo
' '.$j.cycle('a', 'b', 1).PHP_EOL;
        for (
$k = 1; $k<3; $k++) {
            echo
'  '.$k.cycle('c', 'd', 2).PHP_EOL;
        }
    }
}
/**
Output:
1a
1a
  1c
  2d
2b
  1c
  2d
3a
  1c
  2d
4b
  1c
  2d
2b
1a
  1c
  2d
2b
  1c
  2d
3a
  1c
  2d
4b
  1c
  2d
*/

?>
up
0
alan
8 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.
up
0
larax at o2 dot pl
8 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";
up
0
thomas at pixtur dot de
9 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.
up
0
jameslee at cs dot nmt dot edu
9 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
up
0
kouber at php dot net
9 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

}
?>
up
0
Anonymous
9 years ago
Be careful if your static variable is an array and you return
one of it's elements: Other than a scalar variable, elements
of an array are returned as reference (regardless if you
didn't define them to be returned by reference).

<?php
function incr(&$int) {
  return
$int++;
}

function
return_copyof_scalar() {
  static
$v;
  if (!
$v)  
   
$v = 1;
  return(
$v);
}

function
return_copyof_arrayelement() {
  static
$v;
  if (!
$v) {
   
$v = array();
   
$v[0] = 1;
  }
  return(
$v[0]);
}

echo
"scalar: ".
    
incr(return_copyof_scalar()).
    
incr(return_copyof_scalar()).
    
"\n";
echo
"arrayelement: ".
    
incr(return_copyof_arrayelement()).
    
incr(return_copyof_arrayelement()).
    
"\n";
?>

Should print

scalar: 11
arrayelement: 11

but it prints:

scalar: 11
arrayelement: 12

as in the second case the arrays element was returned by
reference. According to a guy from the bug reports the
explanation for this behaviour should be somewhere here in
the documentation (in 'the part with title: "References with
global and static variables"'). Unfortunately I can't find
anything about that here. As the guys from the bug reports
are surely right in every case, maybe there is something
missing in the documentation. Sadly I don't have a good
explanation why this happens, so I decided to document at
least the behaviour.
up
0
info AT SyPlex DOT net
10 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
?>
up
0
Michael Bailey (jinxidoru at byu dot net)
10 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.
up
0
Randolpho
10 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. :)
up
-2
Anonymous
4 months ago
Exemplo #6 don't work on portuguese version.

You need to call Teste() function, not Test()
up
0
jmarbas at hotmail dot com
10 years ago
Whats good for the goose is not always good for the iterative gander. If you declare and initialize the static variable more than once inside a function ie.

<?php
function Test(){
   static
$count = 0;
   static
$count = 1;
   static
$count = 2;
   echo
$count;
}
?>

the variable will take the value of the last declaration. In this case $count=2.

But! however when you make that function recursive ie.

<?php
 
function Test(){
   static
$count = 0;
   static
$count = 1;
   static
$count = 2;

  
$count++;
   echo
$count;
   if (
$count<10){
    
Test();
   }
  }
?>

Every call to the function Test() is a differenct SCOPE and therefore the static declarations and initializations are NOT executed again. So what Im trying to say is that its OK to declare and initialize a static variable multiple times if you are in one function... but its NOT OK to declare and initialize a static variable multiple times if you call that same function multiple times. In other words the static variable is set once you LEAVE a function (even if you go back into that very same function).
up
0
Jack at soinsincere dot com
10 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();

?>
up
0
flobee at gmx dot net
10 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!
up
0
ppo at beeznest dot net
11 years ago
Even if an included file return a value using return(), it's still sharing the same scope as the caller script!

<?php
$foo
= 'aaa';
$bar = include('include.php');
echo(
$foo.' / '.$bar);
?>

where include.php is
<?php
$foo
= 'bbb';
return
$foo;
?>

The output is: bbb / bbb
Not: aaa / bbb
up
0
wjs@sympaticoDOTca
11 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/>";
      }
    }
  }

?>
up
0
carpathia_uk at mail dot com
13 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..";
}
?>
up
0
shevek at anarres dot org
14 years ago
If you include a file from within a function using include(), the included file inherits the function scope as its own global scope, it will not be able to see top level globals unless they are explicit in the function.

<?php
$foo
= "bar";
function
baz() {
    global
$foo; # NOTE THIS
   
include("qux");
}
?>
up
-1
jg at nerd-boy dot net
11 years ago
It's possible to use a variable variable when specifying a variable as global in a function. That way your function can decide what global variable to access in run-time.

<?php
function func($varname)
{
   global $
$varname;

   echo $
$varname;
}

$hello = "hello world!";
func("hello");
?>

This will print "hello world!", and is roughly the same as passing by reference, in the case when the variable you want to pass is global. The advantage over references is that they can't have default parameters. With the method above, you can do the following.

<?php
function func($varname = FALSE)
{
   if (
$varname === FALSE)
     echo
"No variable.";
   else
   {
     global $
$varname;

     echo $
$varname;
   }
}

$hello = "hello world!";
func("hello");                   // prints "hello world!"
func();                          // prints "No variable."
?>
up
-1
heatwave at fw dot hu
11 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,";
}
?>
up
-1
Anonymous
12 years ago
Seems as though when a cookie is saved and referenced as a variable of the same name as the cookie, that variable is NOT global.  If you make a function ro read the value of the cookie, the cooke variable name must be declared as a global.

example:

<?php
function ReturnCookie()
{
       
$cookieName = "Test_Cookie";
        global $
$cookieName;
        if (isset($
$cookieName))
        {
                echo (
"$cookieName is set");
               
$returnvalue = $$cookieName;
        }
        else
        {
               
$newCookieValue = "Test Value";
               
setcookie("$cookieName","$newCookieValue", (time() + 3153600));
                echo (
"made a cookie:" . $newCookieValue ."<BR>");
               
$returnvalue = $newCookieValue;
        }
        echo (
"the cookie that was set is now $returnvalue <BR>");
        return
$returnvalue;
}
?>
up
-1
steph_rondinaud at club-internet dot fr
12 years ago
I'm using PHP 4.1.1

While designing a database access class, I needed a static variable that will be incremented for all instances of the class each time the class connected to the database. The obvious solution was to declare a "connection" class variable with static scope. Unfortunatly, php doesn't allow such a declaration.
So I went back to defining a static variable in the connect method of my class. But it seems that the static scope is not inherited: if class "a" inherit the "db access" class, then the "connection" variable is shared among "a" instances, not among both "a" AND "db access" instances.
Solution is to declare the static variable out of the db access class, and declare "global" said variable in the connect method.
up
-1
tomek at pluton dot pl
12 years ago
When defining static variables you may use such declarations:

<?php
static $var = 1; //numbers
static $var = 'strings';
static
$var = array(1,'a',3); //array construct
?>

but these ones would produce errors:

<?php
static $var = some_function('arg');
static
$var = (some_function('arg'));
static
$var = 2+3; //any expression
static $var = new object;
?>
up
-2
pulstar at ig dot com dot br
10 years ago
If you need all your global variables available in a function, you can use this:

<?php

function foo(parameters) {
  if(
version_compare(phpversion(),"4.3.0")>=0) {
    foreach(
$GLOBALS as $arraykey=>$arrayvalue) {
      global $
$arraykey;
    }
  }
 
// now all global variables are locally available...
}

?>
up
-1
travesty3 at gmail dot com
3 years ago
I was struggling forever to figure this out and finally tried the $GLOBALS["filename"] = $filename approach, and it worked for me.

This happens on one of my machines, on which I installed Zend AMF a few months before my most recent machine. The globals worked fine when calling the PHP script directly from a browser, but when I called the function from my Flash project, which uses Zend AMF to interface with the PHP script, I was seeing this problem, but it was fixed using this approach.
up
-1
pangxiezhou at gmail dot com
2 years ago
assign after static variable declare:

<?php
       
function test() {
                static
$local_var=0;
               
$local_var=9;
                echo
$local_var++;
            }
       
test();
       
test();
       
?>

output:
99

<?php
       
function test() {
                static
$local_var=0;
               
$local_var+=3;
                echo
$local_var++;
            }
       
test();
       
test();
       
?>

output:
37
up
-1
franp at free dot fr
8 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 ...");
}
?>
up
-1
mod
7 years ago
Can not access to global variables from destructor, if obj is not unseted at the end:

<?php

 
class A
  
{
     function
__destruct()
      {
        global
$g_Obj;
        echo
"<br>#step 2: ";
       
var_dump($g_Obj);
      }

     function
start()
      {
        global
$g_Obj;
        echo
"<br>#step 1: ";
       
var_dump($g_Obj);
      }
   };

 
$g_Obj = new A();        // start here
 
$g_Obj->start();
 
$g_Obj = NULL;        // !!! comment line and result will changed !!!

?>

Result, if line is not commented:

#step 1: object(A)#1 (0) { }
#step 2: object(A)#1 (0) { }

Result, if line is commented:

#step 1: object(A)#1 (0) { }
#step 2: NULL
up
-1
sami doesn't want spam at no-eff-eks com
8 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!
up
-2
SID TRIVEDI
6 years ago
<?php
/*
VARIABLE SCOPE : GLOBAL V/S STATIC

If variable $count is defined global as under, instead of static, it does not work well as desired in repeated function calls.

$count = 1; //if not defined STATIC, in each function call, it starts countig from one to 25.
global $count;

which gives folowing output:
0123456789101112131415161718192021222324
Total 24 numbers are printed.
So far 26 function call(s) made.

26272829303132333435363738394041424344454647484950
Total 50 numbers are printed.
So far 52 function call(s) made.
*/

function print_1to50()
{
//    $count = 1;
//    global $count;
   
static $count=1; // Initial assigment of One to $count, static declarion holds the last(previous) value of variable $count in each next function calls.
       
$limit = $count+24;
        while(
$count<=$limit)
        {
        echo
"$count";
       
$count=$count+1;
        }
       
$num_count= $count-1;
        echo
"<br>\n". "Total $num_count numbers are printed.<br>";

        return;
// return statement without parenthesis()or arguments denotes end of a function rather than returning any values to subsequent function call(s).
} // end of while loop

$count=0;
print_1to50();
$count=$count+1;
print
"So far $count function call(s) made.<br><br>";

print_1to50();
$count=$count+1;
print
"So far $count function call(s) made.<br>";
/*
Which gives following output:
12345678910111213141516171819202122232425
Now I have printed 25 numbers.
I have made 1 function call(s).
26272829303132333435363738394041424344454647484950
Now I have printed 50 numbers.
I have made 2 function call(s).
*/

?>
up
-1
huntsbox at pacbell dot net
12 years ago
Not sure of the implications of this but...
You can create nested functions within functions but you must make sure they aren't defined twice, e.g.:

<?php
function norm($a, $b) {
    static
$first_time = true;
    if (
$first_time) {
        function
square($x) {
            return
$x * $x;
        }
       
$first_time = false;
    }
    return
sqrt(square($a) + square($b));
}

print
square(5); // error, not defined yet
print norm(5,4);
print
"<br>";
print
norm(3,2);
print
square(5); // OK
?>

If you don't include the if ($first_time) you get an error saying you can't define square() twice.  Note that square is not local to the function it just appears there.  The last line successfully accesses square in the page scope.  This is not terribly useful, but interesting.
up
-2
vdephily at bluemetrix dot com
9 years ago
Be carefull about nested functions :
<?php
// won't work :
function foo1()
{
 
$who = "world";
  function
bar1()
  {
    global
$who;
    echo
"Hello $who";
  }
}

// will work :
function foo2()
{
 
$GLOBALS['who'] = "world";
  function
bar2()
  {
    global
$who;
    echo
"Hello $who";
  }
}

// also note, of course :
function foo3()
{
 
$GLOBALS['who'] = "world";

 
// won't work
 
echo "Hello $who";

 
// will work
 
global $who;
  echo
"Hello $who";
}
?>
up
-1
emartin at sigb dot net
5 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;

?>
up
-1
jochen_burkhard at web dot de
12 years ago
Please don't forget:
values of included (or required) file variables are NOT available in the local script if the included file resides on a remote server:

remotefile.php:

<?PHP
$paramVal
=10;
?>

localfile.php:

<?PHP
include "http://example.com/remotefile.php";
echo
"remote-value= $paramVal";
?>

Will not work (!!)
up
-2
Ray.Paseur often uses Gmail
9 months ago
Variable "Visibility" in PHP Object Oriented Programming is documented here:
http://php.net/manual/en/language.oop5.visibility.php
up
-3
warbo
1 year ago
An alternative to static variables is to use an anonymous function. Here's an example with a simple counter which goes up on each call:

<?php

// Static version
$staticCounter = function() {
   
// Make $a static, so its value is preserved
   
static $a = 0;
   
$a++;
    return
$a;
};
echo
$staticCounter();
echo
$staticCounter();
echo
$staticCounter();
// Output:
// 1
// 2
// 3

// Closure version
$counterFactory = function () {
   
// We *assign* $a in this function
   
$a = 0;
    return function() use (&
$a) {  // Notice the &
        // We *use* $a in this function
       
$a++;
        return
$a;
    };
};
// The above is a 'counter factory'; when called it returns a counter
$closureCounter1 = $counterFactory();
echo
$closureCounter1();
echo
$closureCounter1();
echo
$closureCounter1();
// Output:
// 1
// 2
// 3

// If we call our 'factory' again, we get another counter, independent of the first
$closureCounter2 = $counterFactory();
echo
$closureCounter1();
echo
$closureCounter2();
echo
$closureCounter1();
echo
$closureCounter2();
// Output (notice that we're calling both counters)
// 4
// 1
// 5
// 2

// We can do it with arguments too
$makeCounterFrom = function($start) {
    return function() use (&
$start) {
       
$start++;
        return
$start;
    };
};
$yearCounter = $makeCounterFrom(2012);
echo
$yearCounter();
echo
$yearCounter();
// Output
// 2013
// 2014
?>

This use of closures may be familiar from Javascript's 'one-shot' functions "(function() {...})()". In PHP we can do this on 2 lines using a variable, or with 'call_user_func'.

It's useful when a regular function isn't enough, but a whole class is overkill.
up
-8
sideshowAnthony at googlemail dot com
2 years ago
It can be nice to use static variables in class member functions.
This avoids a 'class global' like $this->template.
Also, I like the system of get and set using the same function.

<?php

class my_page
{
    public function
template($name=null)
    {
        static
$template = 'templates/page.html';
        if (
$name) $template = "templates/{$name}.html";
        else return
$template;
    }
}

$p = new my_page;
$p->template('product');
include
$p->template();

?>
To Top