Can I share variables between different functions in PHP?

Question

I'll try to explain with an example...

Let's say I have two different functions, and one of them has a defined variable. In the second function, I don't wanna write the same variable again, can I simply use the variable from the first function in the second one WITHOUT redefining it in the second function?

Something like:

function a()
{
  $var = "my variable";
}

function b()
{
 echo $var;
}

Sorry if this questions is a bit silly, but I'm still a beginner =).

Answer 1

$a = 1;
function a(){
  global $a;
  $a = 2;
  }
function b(){
  global $a;
  echo $a;
  }

a();
b();

output:

2

Answer 2

Sure you can do globals, but of PHP 5.3.0+ has anonymous functions, so you can also do closures:

<?php

function a(){
  $a = 1;  
  echo "First: $a, ";
  ++$a;

    // This is a closure. It can gain access to the variables of a() with the 
    // use option.
  $b = function() use ($a) {
      echo "second: $a";  
  };  
  $b();
};
a(); // Outputs: First: 1, second: 2
?>

Try it out at this Codepad example

or probably more useful:

<?php

function a(){
  $a = 1;  
  echo "First: $a, ";
  ++$a;
  $b = function() use ($a) {
      echo "second: $a";  
  };        
  return $b;
};
$fun = a();     // $fun is now $b & $b has access to $a!
$fun();
// Outputs: First: 1, second: 2
?>

Try it out at this Codepad example

From the docs:

Closures may also inherit variables from the parent scope. Any such variables must be declared in the function header. Inheriting variables from the parent scope is not the same as using global variables. Global variables exist in the global scope, which is the same no matter what function is executing. The parent scope of a closure is the function in which the closure was declared (not necessarily the function it was called from).

Answer 3

The cleanest solution here is to make A and B methods of a class and have the common variables as private static variables. This removes the messiness of globals and allows both functions to be globally accessible.

class SomeClass
{
    private static $a = 1;

    public static function a() {
        self::$a = 2;
    }

    public static function b() {
        echo self::$a;
    }
}

You can then call the functions:

SomeClass::a();
SomeClass::b();

Answer 4

I'd do it like this. This is a more common implementation. Remember that functions can be passed parameters and can return values.

// Main
$a = a();
b($a);

function a()
{
  return "my variable";
}

function b(a$)
{
 echo $a;
}

You have the main body of a program, and the variable a$ remains in scope there. Globals are rarely used, and technically never needed.