Very strange behaviour in PHP

Question

I have this code:

$test = 0;
if ($test == "on"){
    echo "TRUE";
}

Result of this code will be:

TRUE

WHY??? My version of PHP: 5.4.10.

http://stackoverflow.com/questions/672040/comparing-string-to-integer-gives-strange-results — markdwhite, Mar 07 '16 at 06:28
@Armen actually,`int` of *ANY* string is 0, that's why it will always be true if compared to 0. (try `intval("anystringyouwanthere")`) — morcen, Mar 07 '16 at 06:32
@Jencen actually i'm not the question asker :), i know that i was answering to question — Armen, Mar 07 '16 at 06:34
@Armen and I was just following up on your answer for the benefit of Weltkind ;) — morcen, Mar 07 '16 at 06:35
@Jencen `echo intval('456-Oh-Hi-This-is-not-0');` Is actually **456** :) — Hanky Panky, Mar 07 '16 at 07:01

Sougata Bose · Accepted Answer · 2016-03-07T06:31:20.687

5

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. These rules also apply to the switch statement. The type conversion does not take place when the comparison is === or !== as this involves comparing the type as well as the value.

$test = 0;
if ($test === "on"){
    echo "TRUE";
}

PHP will convert the string to number to compare. Using ===, will compare the value as well as the type of data.

var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true
var_dump(100 == "1e2"); // 100 == 100 -> true

Docs

edited Mar 07 '16 at 06:31

answered Mar 07 '16 at 06:28

Sougata Bose

31,517
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Yes. === works fine. But 0!="on", I think so :) – Weltkind Mar 07 '16 at 06:29
That's because of the conversion. Check the updates. – Sougata Bose Mar 07 '16 at 06:32

score 4 · Answer 2 · answered Mar 07 '16 at 06:29

Because you are comparing $test with string value not binary value, if you want to compare with string value, try with === comparison, for value + dataType.

In your example, var_dump(0=="on"); always return bool(true).

But when you use var_dump(0==="on"); it will give you bool(false).

Example from PHP Manual:

var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true
var_dump(100 == "1e2"); // 100 == 100 -> true

score 3 · Answer 3 · answered Mar 07 '16 at 06:32

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. These rules also apply to the switch statement. The type conversion does not take place when the comparison is === or !== as this involves comparing the type as well as the value.

So use "===" for comparision.

Refer the link : http://php.net/manual/en/language.operators.comparison.php

score 0 · Answer 4 · answered Mar 07 '16 at 06:28

0

This is because your are doing ==
0 is integer so in this on converted to int which is 0
So your if statement looks like 0==0

For solution You have to use ===

if ($test === "on")

answered Mar 07 '16 at 06:28

Divyesh Savaliya

2,692
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score 0 · Answer 5 · answered Mar 07 '16 at 06:41

In PHP, loose comparison between integer and non-numeric string (i.e string which cannot be interpreted as numeric, such as "php" or in your case "on") will cause string to be interpreted as integer with value of 0. Note that numeric "43", "1e3" or "123" is a numeric string and will be correctly interpreted as numeric value.

I know this is weird.

Very strange behaviour in PHP

5 Answers5