operator strange behaviour

I tried to get answer on the general list, but I didn't get.
I have a little example, which generate strange output.

This is the wrong list, see http://php.net/support

Derick

--
Derick Rethans
http://derickrethans.nl | http://ez.no | http://xdebug.org

Hi!

I tried to get answer on the general list, but I didn't get.
I have a little example, which generate strange output.

$a = 0;
$b = 1;
if ($a = 1 && $b = 0) {
echo 'true ';
var_dump($a);
var_dump($b);
} else {
echo 'false ';
var_dump($a);
var_dump($b);
}
Runing this we get: "flase bool(false) int(0)"

After the precedence table the first step should be evaluating the &&,
and we get something like this: $a = false = 0, which should generate an
error, while there isn't an "lvalue" on the left side of the =.
But doesn't this happen. It seems, that the evaluation of the first =
came before evaluating the &&.

Can someone exactly explain how PHP process this condition?

You are mixing right and left associativity operators without
parenthesis. The PHP doc at:

http://www.php.net/manual/en/language.operators.php

Clearly states that you can do !$a = foo() where the result of foo()
will be assigned to $a. Thus in your example the order of evaluation is:

evaluate $b = 0
evaluate the result of 1 && $b
assign the previous evaluation result to $a

Thus:

$b = 0
1 && 0 = false
$a = false

HTH,
Rob.

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