Assignment Operators
The basic assignment operator is "=". Your first
inclination might be to think of this as "equal to".
Don't. It really means that the the left operand gets set
to the value of the expression on the rights (that is, "gets
set to").
The value of an assignment expression is the value assigned.
That is, the value of "$a = 3" is 3. This allows
you to do some tricky things:
<?php
$a = ($b = 4) + 5; // $a is equal to 9 now, and $b has
been set to 4.
?>
In addition to the basic assignment operator, there are
"combined operators" for all of the binary arithmetic
and string operators that allow you to use a value in an
expression and then set its value to the result of that
expression. For example:
<?php
$a = 3;
$a += 5; // sets $a to 8, as if we had said: $a = $a + 5;
$b = "Hello ";
$b .= "There!"; // sets $b to "Hello There!",
just like $b = $b . "There!";
?>
Note that the assignment copies the original variable to
the new one (assignment by value), so changes to one will
not affect the other. This may also have relevance if you
need to copy something like a large array inside a tight
loop. PHP 4 supports assignment by reference, using the
$var = &$othervar; syntax, but this is not possible
in PHP 3. 'Assignment by reference' means that both variables
end up pointing at the same data, and nothing is copied
anywhere. To learn more about references, please read References
explained.
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