PHP4 User manual: Variables-Basics

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Basis
Fixed variable
Variable scope
Variable for variables
Variables outside of PHP
Description of the variable: in PHP is the name of a dollar end-of-file following variable. Variable names are case sensitive.
The name of the variable is the same as the other tags in PHP. A valid variable name starts with a word line or underscore, followed by some lines, numbers, or underscores. Treated as a regular expression, it would be like this: ' [a-za-z_x7f-xff][a-za-z0-9_x7f-xff]* '
Note: One letter is a-Z, A-Z, and the ASCII character 127 through 255 (0X7F-0XFF).


$var = "Bob";
$Var = "Joe";
echo "$var, $Var"; Output "Bob, Joe"
$4site = ' not yet '; Error The beginning cannot be a number
$_4site = ' not yet '; Effective The beginning can be underlined
$t äyte = ' Mansikka '; Valid: ' Ä ' is ASCII 228.

In PHP 3, a variable is assigned by its value. In other words, when you assign an expression to a variable, the value of the original expression is copied to the destination variable.
This means that assigning a variable's value to another variable, only changing the value of those variables does not affect the other variables. See expressions for more information.
PHP 4 provides another way to assign values to variables: reference assignments. This means that the new variable is simply referencing the original variable (this new variable is just a "pseudonym" or "point") changing the new variable will affect the original variable, and vice versa. This also means that no replication is performed: Therefore, the allocation rate is faster. However, such acceleration is only reflected in complex loops or the allocation of large arrays and objects.
Assign a reference, just the variable that is assigned (the source variable) before adding the "&" number. For example, the following code fragment outputs ' My name is Bob ' two times:

<?php
$foo = ' Bob '; Assign value ' Bob ' to $foo
$bar = & $foo; Reference $foo by $bar.
$bar = "My name is $bar"; Change the $bar ...
Echo $foo; $foo have also been changed.
Echo $bar;
?>

One important hint: only one variable that is specified can be assigned by reference.

<?php
$foo = 25;
$bar = & $foo; This is a valid assignment.
$bar = & (24 * 7); Error: Reference to an unnamed expression.
function test ()
{
return 25;
}
$bar = &test (); Error.
?>