Why 'IF' condition return true for the 0 compared to string in PHP? and how the string parsed as zero?

Question

I faced the below scenario that happened with my web application. I need a exact reason and solution for this

<?php
$var = 0;
if ($var == "StringVal") {
    echo $var;
    echo "Wrong";
} else {
    echo "Right";
}
?>

these code must print

Right

, But it print

0Wrong

What are the possibilities of this problem ?

$var = 'StringVal' is the only manner to make this work. You assign the value 0 to the $var, and that is not the same as 'StringVal'. — Perrykipkerrie, Jun 24 '16 at 07:50
i am checking the 0 value with the string, are you seen the code or not... — Sathish Kumar D, Jun 24 '16 at 07:52
@SathishKumarD Check my answer. When you compare an int with a string the string is converted into an int so "StringVal" would be converted to 0 as it is not a valid number and then 0 == 0 returns true. — Osama Sayed, Jun 24 '16 at 07:54

score 2 · Answer 1 · answered Jun 24 '16 at 07:50

According to the official documentation:

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.

So var_dump(0 == "a"); Would return true as Php tries to parse "a" to a number, if the parsing fails which happens in this case, it returns 0 and then 0 is equal to 0. To overcome this compare the type as well using ===.

Hope this helps.

thank you, after the parsing it will be zero. – Sathish Kumar D Jun 24 '16 at 08:48 — Sathish Kumar D, Jun 24 '16 at 08:48

score 1 · Accepted Answer · answered Jun 24 '16 at 07:51

1

Don't use == for comparison in php. Use === instead.

This way you enforce a type check and this will work as expected. See here for a PHP type comparison tables. There you see that a "Loose comparisons with ==" between e.g. 0 (int) and "php" (string) will return true. Which is not what one would expect.

answered Jun 24 '16 at 07:51

cb0

8,415
9
52
80

1

its really working with the type conversion. but how both are made as equal as true – Sathish Kumar D Jun 24 '16 at 07:55
@SathishKumarD Because if `StringVal` is cast directly to int it's cast to 0 so you are comparing `0 == 0` – Epodax Jun 24 '16 at 08:00

Why 'IF' condition return true for the 0 compared to string in PHP? and how the string parsed as zero?

2 Answers2