Return value of static functions

trexx

I'm playing around with recursive functions and static variables. can anyone explain, why this function does not return the value of $count, even if it displays $count correctly inside the function?

function staticTest()
{
	static $count = 0;
	if( ++$count < 10 )
	{
		echo "in function: $count<br>\n";
		staticTest();
	}
	else
		return $count;
}

echo "function returns: ".staticTest();

daphreeek

The reason for this is that you are calling a function from within a function.

Here is a quick diagram of whats happening and the value of $count the whole way through:

(this aint code - i just want spacing)

echo.... calls staticTest
$count = 0
++ --> $count = 1
1 displayed
staticTest calls static Test (with value of 1 passed on)
      $count = 1
      ++ --> $count = 2
      2 displayed
      staticTest calls static Test (with value of 2 passed on)
            $count = 2
            ++ --> $count = 3
            3 displayed
            staticTest calls static Test (with value of 3 passed on)
                  ....... $count = 9
                          ++ --> $count = 10
                          this function then closes returning 10
                  returns 9
      .........................

a value of 1 is returned to the original function called but nothing is done with this value - the function ends and so doesnt return anything.

You need to make a loop rather than a recursive function for this:

for ($count = 0; $count < 10; $count ++)
     echo "in function: $count<br>\n";

return $count;

Recursive functions are used when the same thing is done over and over. For example, a tree listing of directories:

usage: functionname(dir)

open dir and read all dirs inside it
for each dir found, put back into function so all dirs inside that dir is displayed....

also note that when a funtion is called it creates a new function that is run then PHP continues from where the function was called from so in reality you called a function which called a function which called a function..... and the values where not used when passed back.

Hope that helps - its hard to explain using only words. If you have any questions, just ask.

Matt

trexx

sure... i know that you'd use a simple loop for something like that. it was just an easy example to show that you won't get a return value... the problem occured while i was trying to traverse a tree and display the output (which was a static variable).

but thanks a lot for the explanation!