Variable scope

The scope of a variable is the context within which it is defined. For the most part all PHP variables only have a single scope. This single scope spans included and required files as well. For example:

<?php
$a 
1;
include 
'b.inc';
?>

Here the $a variable will be available within the included b.inc script. However, within user-defined functions a local function scope is introduced. Any variable used inside a function is by default limited to the local function scope. For example:

<?php
$a 
1/* global scope */ 

function test()

    echo 
$a/* reference to local scope variable */ 


test();
?>

This script will not produce any output because the echo statement refers to a local version of the $a variable, and it has not been assigned a value within this scope. You may notice that this is a little bit different from the C language in that global variables in C are automatically available to functions unless specifically overridden by a local definition. This can cause some problems in that people may inadvertently change a global variable. In PHP global variables must be declared global inside a function if they are going to be used in that function.

The global keyword

First, an example use of global:

Example #1 Using global

<?php
$a 
1;
$b 2;

function 
Sum()
{
    global 
$a$b;

    
$b $a $b;


Sum();
echo 
$b;
?>

The above script will output 3. By declaring $a and $b global within the function, all references to either variable will refer to the global version. There is no limit to the number of global variables that can be manipulated by a function.

A second way to access variables from the global scope is to use the special PHP-defined $GLOBALS array. The previous example can be rewritten as:

Example #2 Using $GLOBALS instead of global

<?php
$a 
1;
$b 2;

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


Sum();
echo 
$b;
?>

The $GLOBALS array is an associative array with the name of the global variable being the key and the contents of that variable being the value of the array element. Notice how $GLOBALS exists in any scope, this is because $GLOBALS is a superglobal. Here's an example demonstrating the power of superglobals:

Example #3 Example demonstrating superglobals and scope

<?php
function test_global()
{
    
// Most predefined variables aren't "super" and require 
    // 'global' to be available to the functions local scope.
    
global $HTTP_POST_VARS;
    
    echo 
$HTTP_POST_VARS['name'];
    
    
// Superglobals are available in any scope and do 
    // not require 'global'. Superglobals are available 
    // as of PHP 4.1.0, and HTTP_POST_VARS is now
    // deemed deprecated.
    
echo $_POST['name'];
}
?>

Note:

Using global keyword outside a function is not an error. It can be used if the file is included from inside a function.

Using static variables

Another important feature of variable scoping is the static variable. A static variable exists only in a local function scope, but it does not lose its value when program execution leaves this scope. Consider the following example:

Example #4 Example demonstrating need for static variables

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

This function is quite useless since every time it is called it sets $a to 0 and prints 0. The $a++ which increments the variable serves no purpose since as soon as the function exits the $a variable disappears. To make a useful counting function which will not lose track of the current count, the $a variable is declared static:

Example #5 Example use of static variables

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

Now, $a is initialized only in first call of function and every time the test() function is called it will print the value of $a and increment it.

Static variables also provide one way to deal with recursive functions. A recursive function is one which calls itself. Care must be taken when writing a recursive function because it is possible to make it recurse indefinitely. You must make sure you have an adequate way of terminating the recursion. The following simple function recursively counts to 10, using the static variable $count to know when to stop:

Example #6 Static variables with recursive functions

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

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

Note:

Static variables may be declared as seen in the examples above. From PHP 5.6 you can assign values to these variables which are the result of expressions, but you can't use any function here, what will cause a parse error.

Example #7 Declaring static variables

<?php
function foo(){
    static 
$int 0;          // correct 
    
static $int 1+2;        // correct (as of PHP 5.6)
    
static $int sqrt(121);  // wrong  (as it is a function)

    
$int++;
    echo 
$int;
}
?>

Note:

Static declarations are resolved in compile-time.

References with global and static variables

The Zend Engine 1, driving PHP 4, implements the static and global modifier for variables in terms of references. For example, a true global variable imported inside a function scope with the global statement actually creates a reference to the global variable. This can lead to unexpected behaviour which the following example addresses:

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

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

test_global_ref();
var_dump($obj);
test_global_noref();
var_dump($obj);
?>

The above example will output:


NULL
object(stdClass)(0) {
}

A similar behaviour applies to the static statement. References are not stored statically:

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

    echo 
'Static object: ';
    
var_dump($obj);
    if (!isset(
$obj)) {
        
// Assign a reference to the static variable
        
$obj = &new stdclass;
    }
    
$obj->property++;
    return 
$obj;
}

function &
get_instance_noref() {
    static 
$obj;

    echo 
'Static object: ';
    
var_dump($obj);
    if (!isset(
$obj)) {
        
// Assign the object to the static variable
        
$obj = new stdclass;
    }
    
$obj->property++;
    return 
$obj;
}

$obj1 get_instance_ref();
$still_obj1 get_instance_ref();
echo 
"\n";
$obj2 get_instance_noref();
$still_obj2 get_instance_noref();
?>

The above example will output:


Static object: NULL
Static object: NULL

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

This example demonstrates that when assigning a reference to a static variable, it's not remembered when you call the &get_instance_ref() function a second time.

add a note add a note

User Contributed Notes 54 notes

up
102
warhog at warhog dot net
11 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
58
dodothedreamer at gmail dot com
5 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
34
HOSSEIN doesn&#39;t want spam at TAKI.IR
7 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
4
kouber at php dot net
12 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
8
Anonymous
5 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
13
andrew at planetubh dot com
8 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
2
dexen dot devries at gmail dot com
5 months 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
up
6
larax at o2 dot pl
11 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
2
info AT SyPlex DOT net
12 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
9
php at keith tyler dot com
6 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
7
Anonymous
9 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
12
Stephen Dewey
8 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
Michael Bailey (jinxidoru at byu dot net)
13 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
4
eduardo dot ferron at zeion dot net
6 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
4
danno at wpi dot edu
16 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
2
gried at NOSPAM dot nsys dot by
1 year 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)
?>
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1
simon dot barotte at gmail dot com
9 months 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.
up
5
ddarjany at yahoo dot com
8 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";
}

?>
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3
Jonathan Kenigson
3 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".
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2
zweibieren at yahoo dot com
2 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>
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3
Randolpho
13 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
alan
10 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
2
pedro at worcel dot com
7 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
1
flobee at gmx dot net
13 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
2
moraesdno at gmail dot com
7 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
2
tc underline at gmx TLD ch
11 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
Ray.Paseur often uses Gmail
3 years ago
Variable "Visibility" in PHP Object Oriented Programming is documented here:
http://php.net/manual/en/language.oop5.visibility.php
up
1
thomas at pixtur dot de
12 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
1
jameslee at cs dot nmt dot edu
12 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
1
sami doesn't want spam at no-eff-eks com
11 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
1
jakub dot lopuszanski at nasza-klasa dot pl
7 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
0
Semyon Naitur
28 days 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'
up
0
pogregoire##live.fr
10 months 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).
?>
up
0
emartin at sigb dot net
8 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
0
nullhility at gmail dot com
8 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
franp at free dot fr
11 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
0
wjs@sympaticoDOTca
14 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
heatwave at fw dot hu
14 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
0
steph_rondinaud at club-internet dot fr
15 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
0
admin at essentialhost dot com
15 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
0
shevek at anarres dot org
17 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
carpathia_uk at mail dot com
16 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
-1
Ganlv
1 year 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);'
up
-1
Anonymous
3 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
up
-1
jmarbas at hotmail dot com
13 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
-2
Leigh Harrison
8 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
akam at akameng dot com
8 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(){
$_POST['foo'][] = range(8, 10);
}
?>
Note: the key must not be passed by the page via _POST method by the form, else the value will be over written
up
-2
lgrk
9 years ago
Useful function:
<?php
function cycle($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
*/

?>
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-2
marcin
11 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
nino dot skopac at gmail dot com
1 year 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.
up
-2
ppo at beeznest dot net
14 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
-2
jg at nerd-boy dot net
14 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
-3
jochen_burkhard at web dot de
15 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
-3
Jack at soinsincere dot com
13 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();

?>
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