Programming PHP

The old value of $black is lost. Instead, $black is now another name for the value
that is stored in $white:
$big_long_variable_name = "PHP";
$short =& $big_long_variable_name;
$big_long_variable_name .= " rocks!";
print "\$short is $short\n";
print "Long is $big_long_variable_name\n";
$short is PHP rocks!
Long is PHP rocks!
$short = "Programming $short";
print "\$short is $short\n";
print "Long is $big_long_variable_name\n";
$short is Programming PHP rocks!
Long is Programming PHP rocks!
After the assignment, the two variables are alternate names for the same value.
Unsetting a variable that is aliased does not affect other names for that variable’s
value, though:
$white = "snow";
$black =& $white;
unset($white);
print $black;
snow
Functions can return values by reference (for example, to avoid copying large strings
or arrays, as discussed in Chapter 3):
function &ret_ref() { // note the &
$var = "PHP";
return $var;
}
$v =& ret_ref(); // note the &
Variable Scope
The scope of a variable, which is controlled by the location of the variable’s declaration,
determines those parts of the program that can access it. There are four types of
variable scope in PHP: local, global, static, and function parameters.
Local scope
A variable declared in a function is local to that function. That is, it is visible only to
code in that function (including nested function definitions); it is not accessible outside
the function. In addition, by default, variables defined outside a function (called
global variables) are not accessible inside the function. For example, here’s a function
that updates a local variable instead of a global variable:
function update_counter ( ) {
$counter++;
}
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Variables | 31