Operator &&

[wennergr]

Consider the following example:

if( expr_a && expr_b ).

If expr_a returns false, Am I then garanted that expr_b won't be evaluated.
(if expr_a is failes, then so does the whole if expression).

A more realistic example:

if( userdata_ok($id) && adduser($id) )
{
/ OK /
}
else
{
/ Failed /
}

[laserlight]

I'd say the answer is yes due to lazy evaluation.

[PHPMagician]

http://ie2.php.net/manual/en/language.operators.php#language.operators.precedence

[wennergr]

Originally posted by PHPMagician
http://ie2.php.net/manual/en/language.operators.php#language.operators.precedence

That document does not say anything about if expr_b will be
evaluated or not, just that operator && is left associative.

But, as laserlight said, expr_b is probobly not evaluated due to
lazy evaluation. I was hoping that php had som kind of standard
that defined cases like this (maybe something like, K&R ANSI C/C++)

/Wennergr

[PHPMagician]

You're right, sorry for posting the link. My bad. But yes, the expr_b will not be evaluated. However, if for some reason you did want the expr_b to be evaluated you could use & (bitwise AND). For example:

<?php
if (expr_a() & expr_b()) {
    echo "Both returned true";
}
?>

Even if expr_a returns false, expr_b() will be evaluated. They will be bitwise then which means if both are 1, 1 will be the result. Any other combination (ie. 0 & 1, 1 & 0, 0 & 0) will return 0. So only if both functions return false will that constructure data be evaluated.

A similar concept is apparent with the operators || and |.