PHP Sanity Check, conditional / comparison

Question

Can someone, for the love of all things natural, please explain why this is happening?

$code = 0;
echo $code == 'item_low_stock' ? 'equal' : 'not equal';

// RESULT: "equal"

???

A line of code in my app just suddenly stopped working properly, I haven't edited anything around it, changed my php version, anything. When the $code variable contains 0, it is passing as true when I compare it to the string 'item_low_stock'.

I can post the original block of code, but I boiled it down to this comparison and this is what I found.

Halp.

EDIT: PHP version is 5.3.10.

What you want to use is the equality operator, ===, which will also ensure that the types being compared are the same. Thus, if $code is not 'item_low_stock' or not a string, the comparison works as expected. — user50049
– user50049, Commented Dec 4, 2012 at 3:04

Sampson · Accepted Answer · 2012-12-04 03:05:05Z

4

The documentation makes it clear that the two values on either side of == are tested after type juggling. When cast to an integer, your string becomes 0. Try the following:

echo (int) 'item_low_stock'; // 0

Run it: http://codepad.org/z7LIEumk

If you don't want to engage in type juggling, use === or !== instead. This tests whether the two values are * identical*, meaning same value and type.

answered Dec 4, 2012 at 3:05

Sampson

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1 Comment

user50049 Over a year ago

Worth mentioning the equality operator, so she gets the results she's expecting.

zerkms · Accepted Answer · 2012-12-04 03:02:12Z

2

When one of operands is a number - then php casts another one to a number as well.

So item_low_stock string casted to number is 0, thus it equals to 0, thus it's true

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

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically.

answered Dec 4, 2012 at 3:02

zerkms

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1 Comment

jessica Over a year ago

Wow, amazing.. insane! How have I never come across this in all my years of php developing? Thank you! I guess the change in my app was with a library that hadn't been passing the value of 0 in the $code variable before, prior, the codes had all been strings.

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