Predefined Variables
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.
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. Trying to assign values to these variables which are the result of expressions will cause a parse error.
Example #7 Declaring static variables
<?php
function foo(){
static $int = 0; // correct
static $int = 1+2; // wrong (as it is an expression)
static $int = sqrt(121); // wrong (as it is an expression too)
$int++;
echo $int;
}
?>
Note:
Static declarations are resolved in compile-time.
Note:
Using global keyword outside a function is not an error. It can be used if the file is included from inside a function.
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
User Contributed Notes
Variable scope - [62 notes]
warhog at warhog dot net ¶
7 years ago
travesty3 at gmail dot com ¶
2 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.
Anonymous ¶
5 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' );
?>
php at keith tyler dot com ¶
2 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.
HOSSEIN doesn't want spam at TAKI.IR ¶
2 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 />';
}
?>
carpathia_uk at mail dot com ¶
12 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..";
}
?>
nullhility at gmail dot com ¶
4 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.]
jakub dot lopuszanski at nasza-klasa dot pl ¶
3 years ago
If you use __autoload function to load classes' definitons, beware that "static local variables are resolved at compile time" (whatever it really means) and the order in which autoloads occur may impact the semantic.
For example if you have:
<?php
class Singleton{
static public function get_instance(){
static $instance = null;
if($instance === null){
$instance = new static();
}
return $instance;
}
}
?>
and two separate files A.php and B.php:
class A extends Singleton{}
class B extends A{}
then depending on the order in which you access those two classes, and consequently, the order in which __autoload includes them, you can get strange results of calling B::get_instance() and A::get_instance().
It seems that static local variables are alocated in as many copies as there are classes that inherit a method at the time of inclusion of parsing Singleton.
Stephen Dewey ¶
3 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');
?>
pangxiezhou at gmail dot com ¶
11 months 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
Anonymous ¶
11 months 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
$p static: changed
dodothedreamer at gmail dot com ¶
1 year ago
Note that unlike Java and C++, variables declared inside blocks such as loops or if's, will also be recognized and accessible outside of the block, so:
<?php
for($j=0; $j<3; $j++)
{
if($j == 1)
$a = 4;
}
echo $a;
?>
Would print 4.
wjs@sympaticoDOTca ¶
10 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/>";
}
}
}
?>
shevek at anarres dot org ¶
13 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 $foo; # NOTE THIS
include("qux");
}
?>
lgrk ¶
5 years ago
Useful function:
<?php
function cycle($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
*/
?>
mod ¶
6 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
sami doesn't want spam at no-eff-eks com ¶
6 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!
tc underline at gmx TLD ch ¶
7 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
vdephily at bluemetrix dot com ¶
8 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 $who";
}
?>
huntsbox at pacbell dot net ¶
11 years ago
Not sure of the implications of this but...
You can create nested functions within functions but you must make sure they aren't defined twice, e.g.:
<?php
function norm($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.
danno at wpi dot edu ¶
11 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
eduardo dot ferron at zeion dot net ¶
2 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".
pedro at worcel dot com ¶
2 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
moraesdno at gmail dot com ¶
3 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>";
?>
akam at akameng dot com ¶
3 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
emartin at sigb dot net ¶
3 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;
?>
Leigh Harrison ¶
4 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
andrew at planetubh dot com ¶
4 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().
ddarjany at yahoo dot com ¶
4 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";
}
?>
SID TRIVEDI ¶
5 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).
*/
?>
alan ¶
6 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.
larax at o2 dot pl ¶
7 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";
franp at free dot fr ¶
7 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 ...");
}
?>
marcin ¶
7 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
?>
thomas at pixtur dot de ¶
7 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.
jameslee at cs dot nmt dot edu ¶
8 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
kouber at php dot net ¶
8 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
}
?>
Anonymous ¶
8 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.
pulstar at ig dot com dot br ¶
8 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...
}
?>
info AT SyPlex DOT net ¶
8 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
?>
Michael Bailey (jinxidoru at byu dot net) ¶
9 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.
Randolpho ¶
9 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. :)
jmarbas at hotmail dot com ¶
9 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).
Jack at soinsincere dot com ¶
9 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();
?>
flobee at gmx dot net ¶
9 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!
ppo at beeznest dot net ¶
9 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 $foo;
?>
The output is: bbb / bbb
Not: aaa / bbb
jg at nerd-boy dot net ¶
10 years ago
It's possible to use a variable variable when specifying a variable as global in a function. That way your function can decide what global variable to access in run-time.
<?php
function func($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."
?>
heatwave at fw dot hu ¶
10 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,";
}
?>
Anonymous ¶
11 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;
}
?>
jochen_burkhard at web dot de ¶
11 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 (!!)
steph_rondinaud at club-internet dot fr ¶
11 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.
tomek at pluton dot pl ¶
11 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;
?>
Anonymous ¶
3 months ago
I had code not too unlike this:
<?php
function foo() {
static $s = 0;
if ($s == 0) {
echo 'setting $s to "foo"<br>';
$s = "foo";
}
}
// a little test
foo();
foo();
foo();
?>
Which prints 'setting $s to "foo"' three times.
The code needs to be:
<?php
function foo() {
static $s = '';
if ($s == '') {
echo 'setting $s to "foo"<br>';
$s = "foo";
}
}
?>
Anonymous ¶
2 years ago
You can use the global function to use variables in classes when included. This means you can have a file such as "MainSettings.php" (Similar to MediaWiki's localsettings) with DB info, etc.
<?php
require("MainSettings.php");
class Foo {
function Bar() {
global $testVariable;
return $testVariable;
}
}
?>
MainSettings.php:
<?php
$testVariable = "This works!";
?>
Without the global you would get a E_NOTICE saying that $testVariable is undefined.
Thomas ¶
5 years ago
It might be worth noting in the article that you shouldn't define magic values at global level and use "global" to access them in a function - like I did in the past few years.
Use define() instead.
admin at essentialhost dot com ¶
11 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.
marc ¶
1 year ago
<?php
function foo(){
static $int = 0; // correct
static $int = 1+2; // wrong (as it is an expression)
static $int = sqrt(121); // wrong (as it is an expression too)
$int++;
echo $int;
}
?>
Please update this example it is not completely correct, it can be confusing.
<?php
function foo(){
static $int = 0; // correct
static $int = 1+2; // wrong (as it is an NON-CONSTANT expression)
static $int = sqrt(121); // wrong (as it is an NON-CONSTANT expression too)
$int++;
echo $int;
}
?>
Expressions can be assigned to static variables, they just have to be constants, nothing dynamic, no calculations etc
sideshowAnthony at googlemail dot com ¶
1 year 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 $p->template();
?>
dr_dazzit at yahoo dot co dot uk ¶
1 year ago
Functions are always global. I've had fun and games in the past with the global keyword with nested functions. So for teleporting variables between functions I've occasionally adopted this simple method.
<?php
function &teleport($vars = null){
static $toSave = array();
if($vars){
foreach($vars as $k=>&$v)
$toSave[$k] = $v;
}
return($toSave);
}
function myFuncA(){
extract(teleport(),EXTR_REFS);
$a = array('a'=>1,'b'=>2);
$b = "An arbitrary value of no consequence\n";
teleport(array('a'=>$a,'b'=>$b));
}
function myFuncB(){
extract(teleport(),EXTR_REFS);
$b = "Now this is of Consequence\n";
$c = "Another of Consequence\n";
teleport(array('c'=>$c));
}
function myFuncC(){
extract(teleport(),EXTR_REFS);
// $a,$b,$c are now in current scope
print_r(get_defined_vars());
print_r($a);
echo($b);
echo($c);
}
myFuncA();
myFuncB();
myFuncC();
?>
Purists might shout something about "USE A CLASS" etc...
Maybe but sometimes you might not want to or need to.
warbo ¶
5 months 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 $yearCounter();
// Output
// 2013
// 2014
?>
This use of closures may be familiar from Javascript's 'one-shot' functions "(function() {...})()". In PHP we can do this on 2 lines using a variable, or with 'call_user_func'.
It's useful when a regular function isn't enough, but a whole class is overkill.
carlos dot garciadm at gmail dot com ¶
2 years ago
If you will work with a lot of global variables, using extract($GLOBALS) has some problems if you will modify the global variables inside a function:
Example:
<?php
$a = 1;
function foo() {
extract($GLOBALS);
$a = 5;
}
foo();
print $a; // will print "1" instead of "5"
?>
The problem here is that when doing extract you are only getting the values of all globals in that moment, if you modify a variable, only the local variable will be modified. So you will need to use global $a .
This is what I did in a script using a lot of global variables, please note that this is the case of 20 or 30 variables. Using global would be a real pain, and I didn't want to use objects.
<?php
$a = 1;
function globals(){
$vars = array();
foreach($GLOBALS as $k => $v){
$vars[] = "$".$k;
}
return "global ". join(",", $vars).";";
}
function foo(){
eval(globals()); // just insert this line at the beggining of each function
$a = 5;
}
foo();
print $a; // will print "5"
?>
Carlos Dubus