Comparing numeric strings

Question

From the question Type-juggling and (strict) greater/lesser-than comparisons in PHP

I know PHP interpret strings as numbers whenever it can.

"10" < "1a"  => 10 less than 1      expecting  false 
"1a" < "2"   => 1 less than 2       expecting  true
"10" > "2"   => 10 greater than 2   expecting  true

But in the case of "10" < "1a" php returns true.

I am not understanding the concept please help me to clarify it.

Edit:

But when I add "10" + "1a" it returns 11 that means php interprets "10" as 10 and "1a" as 1. Is that correct?

score 6 · Answer 1 · answered Nov 01 '13 at 09:34

6

A comes after 9. You can see this in this string, sorted from low to high.

0123456789abcdefghijklmnopqrstuvwxyz

So 10 is lower than 1a.

answered Nov 01 '13 at 09:34

Steyx

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Nice and simple. Thanks – Kiren S Nov 01 '13 at 10:00

TiMESPLiNTER · Accepted Answer · 2013-11-01T09:58:37.013

4

It's easy 1a is not numeric. So PHP compares string(2)"10" against string(2)"1a" and numbers are before alpha characters in the most text encoding tables (have a look at the ASCII or UTF-8 character tables).

So 1 of 10 is equals 1of 1a and 0 of 10 is lower than a of 1a. That results in 10 is lower than 1a.

edited Nov 01 '13 at 09:58

answered Nov 01 '13 at 09:31

TiMESPLiNTER

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I got it. But when adding it is another result. Please see my edit – Kiren S Nov 01 '13 at 09:54
Mathematic operations are another shoe that's true cause PHP can not add two strings but compare two strings. This is why PHP propably extract the numbers out of `1a` if you try to add it. **But you should never ever do something like that!** Even if PHP don't treat it with an error ;-). That's how you would add a pear in a bucket full of apples. – TiMESPLiNTER Nov 01 '13 at 09:56

score 2 · Answer 3 · answered Nov 01 '13 at 09:35

2

If you want to be sure, that you comparing numbers, put (type) before variable:

(int)"10" < (int)"1a"
(int)"1a" < (int)"2"
(int)"10" > (int)"2"

answered Nov 01 '13 at 09:35

KiraLT

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serghei · Answer 4 · 2013-11-01T09:55:19.387

0

Maybe you first need to use regular expressions?

For example:

$str = '1a';
$str = preg_replace ("/[^0-9\s]/","", $str);
var_dump((int)$str); // int 1

edited Nov 01 '13 at 09:55

answered Nov 01 '13 at 09:47

serghei

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Praveen D · Answer 5 · 2013-11-01T09:44:42.183

-1

Read at this link to get what happens when comparing value of two different data types.

Use type juggling to compare values of two different data type.

(int)"10" < (int)"1a"  result will be false
(int)"1a" < (int)"2"  result will be true

edited Nov 01 '13 at 09:44

answered Nov 01 '13 at 09:36

Praveen D

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That's not type juggling, that's type casting. Check the page you linked to, it's under a different heading. Type juggling is what PHP does automatically, type casting is when you tell it what to do explicitly using e.g. (int). – Niall Aug 29 '17 at 11:48

Comparing numeric strings

5 Answers5