Oracle Tips by Burleson

These are variables currently registered to a script’s session. They are analogous to the old $HTTP_SESSION_VARS array, still available, but deprecated. See the session handling functions section for more information.

The Sessions, GET and POST method is covered in detail in the next chapter.  For now, focus remains on PHP and functions. 

In the example above, the global variable is a variable from the main program imported into the scope of the function. Global variables should not be confused with staticvariables, which retain their value between invocations. 

Before static variables are explained, another small detail from the example above should be clarified: the functions “isset” and “strlen”.  The function “strlen” is the same as in C or C++ and returns the length of the string given as the argument. The “isset” checks whether the variable given as its argument is defined (“set”).  A variable is defined when it is referenced for the first time. These two functions are two among the many useful functions provided by the authors of PHP.

Focus can now return to staticvariables. What are they? They are variables that retain the value between function invocations. Every local variable is normally created at the beginning of the function invocation and destroyed when the function returns. This means that a “normal” variable is created anew for each invocation. Static variables are not recreated each time a function is called.

How are they declared? It is simple. Instead of using the word “global”, the word “static ” is used. What are they used for? Static variables are mainly used as a counter, because they count the number of times a function is invoked. The example for the static variables is extremely simple and is a re-engineered example9.php, with the preferred factorial function.                

Example 9a:

$ cat ./example9a.php
#!/usr/local/bin/php
<?php
function factorial($n) {
   static $count=0;
   $count++;
   if ($n>1) return($n*factorial($n-1));
   else { echo "Number of factorial invocations:$count\n";
          return(1);
   }
}
$a=6;
$b=factorial($a);
echo "Factorial($a)=$b\n";
?>

Variable $count is declared as staticand initialized to zero. Without the keyword “static”, the variable is created during each invocation, set to zero and incremented by one. The finalnumber of invocations printed is “1” with the variable $count declared as static. 

The output looks like it should:

$ ./example9a.php
Number of factorial invocations:6
Factorial(6)=720

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