On Sat, 2004-10-30 at 14:45, Hodicska Gergely wrote:
> 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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