Operand precedence of assignment in PHP

Question

Is it just me or is it just odd to have the precedence of assignment be higher than any other operator? Example in PHP I just came across:

    function test($param1) {
        $result = TRUE;
        for ($i = 0; $i <; strlen($param1); $i++) {
            if (!(ord($param1[$i]) >= 65 && ord($param1[$i]) <=90)) {
                $result = $result && FALSE;
            }
        }
        return $result;
    }

The intention when calling this function is to check whether a string has all characters in the range A-Z (If there are better ways it would be great to hear about them). The key part being the $result = $result && FALSE which I had thought would evaluate the right side to FALSE then assign $result that value.

But No. This little bug/feature took some tracking down.

It appears that the the assignment of $result = $result is performed first then to no-one the operation TRUE && FALSE; is carried out. I actually had to give explicit direction to say $result = ($result && FALSE); which does seem very bizarre.

Anyway, I don't see how this is particularly useful 'feature' to have? Any ideas or am I missing something really basic?

Hmm, docs say that && has higher precedence than assignment. — Alex Howansky, Nov 15 '12 at 18:26
http://php.net/manual/en/language.operators.precedence.php -- `&&` has higher precedence than `=`, so you appear to be incorrect (and you also appear to be incorrect based on a test-script I wrote). — Explosion Pills, Nov 15 '12 at 18:26
Just `return FALSE;` inside the if() check. No need to keep looking once you find one bad value. — Alex Howansky, Nov 15 '12 at 18:30

score 1 · Accepted Answer · edited May 23 '17 at 11:43

1

If there are better ways it would be great to hear about them

ctype_upper()

It appears that the assignment is performed first then the && operation

You are mistaken. You are confused by the combination of your (incorrect) test of characters against integers and the reassignment of $result in a tight loop.

As noted in the comments, fail early.

edited May 23 '17 at 11:43

Community

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answered Nov 15 '12 at 18:34

Jason McCreary

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Dang, I always forget about those ctype functions... – Alex Howansky Nov 15 '12 at 18:38
@Alex Howansky, no worries. I'm here to help [be a better PHP Developer](http://jason.pureconcepts.net/2012/08/better-php-developer/) :) – Jason McCreary Nov 15 '12 at 18:39
@JasonMcCreary thanks for spotting the missing ords, was a typo in the question. The behaviour was still there in the original code though. – mykhamill Nov 15 '12 at 20:21

score 0 · Answer 2 · edited Nov 15 '12 at 18:30

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characters are not ints in PHP, you need to call ord on them to get meaningful comparison with the number literals.

as far as better ways are concerned, how about preg_match() with ^[A-Z]*$?

so the real problem with your code is that it never enters the innermost if.

edited Nov 15 '12 at 18:30

Mike Mackintosh

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answered Nov 15 '12 at 18:27

just somebody

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Sorted the question regarding the ords. They were in the original code that caused the behaviour. Thanks for the tip on preg_match(). – mykhamill Nov 15 '12 at 20:24
if the code you paste here is not the code that you actually use (cut down to the necessary minimum and still exhibiting the unexpected behavior), then you probably won't get meaningful answers here. like, maybe your *real* code has `$result = $result & false` (not the single ampersand)... we'll never know. – just somebody Nov 16 '12 at 11:02

Operand precedence of assignment in PHP

2 Answers2