Programming PHP

update_counter( );
update_counter( );
echo "Global counter is $counter\n";
Static counter is now 1
Static counter is now 2
Global counter is 10
Function parameters
As we’ll discuss in more detail in Chapter 3, a function definition can have named
parameters:
function greet ($name) {
echo "Hello, $name\n";
}
greet("Janet");
Hello, Janet
Function parameters are local, meaning that they are available only inside their functions.
In this case, $name is inaccessible from outside greet( ).
Garbage Collection
PHP uses reference counting and copy-on-write to manage memory. Copy-on-write
ensures that memory isn’t wasted when you copy values between variables, and reference
counting ensures that memory is returned to the operating system when it is
no longer needed.
To understand memory management in PHP, you must first understand the idea of a
symbol table. There are two parts to a variable—its name (e.g., $name), and its value
(e.g., "Fred"). A symbol table is an array that maps variable names to the positions of
their values in memory.
When you copy a value from one variable to another, PHP doesn’t get more memory
for a copy of the value. Instead, it updates the symbol table to say “both of these
variables are names for the same chunk of memory.” So the following code doesn’t
actually create a new array:
$worker = array("Fred", 35, "Wilma");
$other = $worker; // array isn't copied
If you then modify either copy, PHP allocates the memory and makes the copy:
$worker[1] = 36; // array is copied, value changed
By delaying the allocation and copying, PHP saves time and memory in a lot of situations.
This is copy-on-write.
Each value pointed to by a symbol table has a reference count, a number that represents
the number of ways there are to get to that piece of memory. After the initial
assignment of the array to $worker and $worker to $other, the array pointed to by the
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