PHP/Variable
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PHP variables are case-sensitive labels preceded by a dollar sign ("$"). Variable names can contain letters, numbers, and underscores, but must start with a letter or underscore.
Being a loosely typed language, PHP variables do not need to be declared with a type before they are first used. Variables can be assigned a value of any type at any time.
One special variable, $this, is defined by PHP and cannot be reassigned. It's used by objects to refer to themselves.
Scope [edit]
Within a function a variable has local scope by default. Variables defined outside a function or class definition are in global scope. To use a global variable within a function, the global keyword must be used.
Static [edit]
A static variable is one which retains its value across function calls. Instead of being instantiated upon each call to a function, a static variable will still have the value it was last assigned when the function was last called.
A static variable can be assigned a default value when declared.
For example:
function foo() { static $counter = 0; $non_static = 0; $counter++; $non_static++; echo 'counter: ', $counter, ', non-static: ', $non_static, "\n"; } foo(); foo(); foo(); // Output: // counter: 1, non-static: 1 // counter: 2, non-static: 1 // counter: 3, non-static: 1
