asked on

php string comparison, why the same?

Hi all,

When I test the string comparison functions, I do not understand why they are equal.

This is the script:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Comparaison de chaînes de caractères</title>
</head>
<body>
<?php
$str1 = "033123456789";
$str2 = "+33456789087";

$sub1 = substr($str1, 0, 3);
$sub2 = substr($str2, 0, 3);

echo $sub1 . " -- " . $sub2 . "<br>";

if (strcmp($sub1, $sub2) !== 0) {
	echo "The strings are equal.<br>";
} else {
	echo "The strings are not equal.<br>";
}

?>
</body>
</html>

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And this is what I have in my browser:

033 -- +33
The strings are equal.

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My version of PHP is 5.2.17

FarWest

it looks like treating '+' as 0

I think you can do work around by comparing sha1 output

if (strcmp(sha1($sub1), sha1($sub2)) !== 0) {
	echo "The strings are equal.<br>";
} else {
	echo "The strings are not equal.<br>";
}

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Brian Tao

Because you're echoing "The strings are equal.<br>" when they are not!
Change the !== to == in line 17.

Richard Coffre

ASKER

Oups,

The weird code is:

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Comparaison de chaînes de caractères</title>
</head>
<body>
<?php
$str1 = "033123456789";
$str2 = "+33456789087";

$sub1 = substr($str1, 0, 3);
$sub2 = substr($str2, 0, 3);

echo $sub1 . " -- " . $sub2 . "<br>";

if ($sub1 == $sub2) {
	echo "The strings are equal.<br>";
} else {
	echo "The strings are not equal.<br>";
}

?>
</body>
</html>

Open in new window

The output is:

033 -- +33
The strings are equal.

Open in new window

ASKER CERTIFIED SOLUTION

Gary

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Brian Tao

According to http://php.net/manual/en/language.operators.comparison.php, when using "==", it evaluates to TRUE if $a is equal to $b after type juggling, meaning that:

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 you should use either strcmp() or the identical operator "===" to compare possible numerical strings.

Gary

Congratulations for repeating what I already said

Brian Tao

@Gary,
Come on! I think you've seen some of my comments to other questions. I don't repeat what other people already said.
And you have posted some comments regarding that people may have opened the page, enter their comments, but didn't realize that their answers are very similar to others' until they hit the Submit button.
Plus that if it were not for my previous comment (45 minutes before yours), the author would not even know he had pasted the wrong script.
Anyway, I'll try to send you some congratulations next time when I see you posting similar answers following others. ^^

Cheers!

Gary

My answer was based on his real code.
You repeated the exact same analogy of my comment
If someone comes up with the same answer within a few minutes then I won't bitch about it unless it is a 10 word comment that consists of a link and copy/paste which your comment barely passes

Anyway, I'll try to send you some congratulations next time when I see you posting similar answers following others

Invariably (99%) where I post a similar comment to what has already been posted in the time it took to write the comment then I will delete unless it adds something else to the discussion/answer

The author posting the wrong code is irrelevant - many times authors post a synopsis of their code that is irrelevant as they have removed the important parts or thought this 3 line version of their code is enough.

Brian Tao

unless it adds something else to the discussion/answer

Yes, that's why I didn't delete mine. I thought an explanation from PHP official site would be worth referencing.