CODEWITHSUNDEEP
phpoperator-precedence
user1508429
user1508429

Reputation: 35

Operator precedence error in PHP (AND comparison)

In my code I have this comparison:

$check_iter_C_sfavorito = ($tipo_iter_sfavorito[$id_loop][$k_tg] == 'C') AND (!(abs(@$delta_salto_check_sfavorito) < 0.001));

which result as true even when:

($tipo_iter_sfavorito[$id_loop][$k_tg] == 'C') ====>>>> is true

and

(!(abs(@$delta_salto_check_sfavorito) < 0.001)) ====>>>> is false

While it is OK if I use the operator "&&" instead of "AND", PHP operator precedence means this should not give this error, because of parentheses!

Thanks for the quick answers to both the "Mar* B*". I changed the code as follows:

$check_iter_C_sfavorito = (($tipo_iter_sfavorito[$id_loop][$k_tg] == 'C') AND (!(abs(@$delta_salto_check_sfavorito) < 0.001)));

... and it is OK!

Upvotes: 0

Views: 184

Answers (2)

Marc B
Marc B

Reputation: 360592

It's directly specified in the documentation: http://php.net/manual/en/language.operators.precedence.php

and and or bind at LOWER precedence than =, so your statement with and is seen as

($foo = 'bar') AND 'baz';

Remember that in PHP, the result of an assignment is the value being assigned. This is how the standard "check for db failure" code works:

$result = mysql_query($sql) or die(msyql_error());

because or binds lower than =, the statement is parsed as:

($result = mysql_query($sql)) or die(mysql_error());

If the DB query fails, it returns false, which gets assigned to $result. The result of that assignment is also false, which gets ored with the die cal, causing the script to abort. If the query SUCCEEDS it returns a non-false value (the statement handle), and the or never kicks in because of boolean shortcircuiting.

Upvotes: 1

Mark Baker
Mark Baker

Reputation: 212412

Equivalent of

($check_iter_C_sfavorito = ($tipo_iter_sfavorito[$id_loop][$k_tg] == 'C')) AND (!(abs(@$delta_salto_check_sfavorito) < 0.001));

because AND has lower precedence than the assignment (=)

Upvotes: 1

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