PHP Fatal error: Using $this when not in object context

In my index.php I'm loading maybe foobarfunc() like this:

 foobar::foobarfunc();  // Wrong, it is not static method

but can also be

$foobar = new foobar;  // correct$foobar->foobarfunc();

You can not invoke method this way because it is not static method.

foobar::foobarfunc();

You should instead use:

foobar->foobarfunc();

If however you have created a static method something like:

static $foo; // your top variable set as staticpublic static function foo() {    return self::$foo;}

then you can use this:

foobar::foobarfunc();

You are calling a non-static method :

public function foobarfunc() {    return $this->foo();}

Using a static-call :

foobar::foobarfunc();

When using a static-call, the function will be called (even if not declared as static), but, as there is no instance of an object, there is no $this.

So :

• You should not use static calls for non-static methods
• Your static methods (or statically-called methods) can't use $this, which normally points to the current instance of the class, as there is no class instance when you're using static-calls.

Here, the methods of your class are using the current instance of the class, as they need to access the $foo property of the class.

This means your methods need an instance of the class -- which means they cannot be static.

This means you shouldn't use static calls : you should instanciate the class, and use the object to call the methods, like you did in your last portion of code :

$foobar = new foobar();$foobar->foobarfunc();

For more informations, don't hesitate to read, in the PHP manual :

• The Classes and Objects section
• And the Static Keyword page.

Also note that you probably don't need this line in your __construct method :

global $foo;

Using the global keyword will make the $foo variable, declared outside of all functions and classes, visibile from inside that method... And you probably don't have such a $foo variable.

To access the $foo class-property, you only need to use $this->foo, like you did.

If you are invoking foobarfunc with resolution scope operator (::), then you are calling it statically, e.g. on the class level instead of the instance level, thus you are using $this when not in object context. $this does not exist in class context.

If you enable E_STRICT, PHP will raise a Notice about this:

Strict Standards: Non-static method foobar::foobarfunc() should not be called statically

Do this instead

$fb = new foobar;echo $fb->foobarfunc();

On a sidenote, I suggest not to use global inside your classes. If you need something from outside inside your class, pass it through the constructor. This is called Dependency Injection and it will make your code much more maintainable and less dependant on outside things.