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Doc Bug #78934 What do mbstring functions return when they fail?
Submitted: 2019-12-09 00:03 UTC Modified: 2021-09-09 16:46 UTC
From: anthony_rutledge_101 at yahoo dot com Assigned: cmb (profile)
Status: Not a bug Package: mbstring related
PHP Version: Irrelevant OS:
Private report: No CVE-ID: None
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 [2019-12-09 00:03 UTC] anthony_rutledge_101 at yahoo dot com 
Description:
------------
---
From manual page: https://php.net/function.mb-substr
---

Hi. Short and sweet. Would you please add what mb_substr() returns when it fails to the manual page? Thank you. I would have given you the answer, but my PHP 7.2.7 on Windows (legacy) does not have the multi-byte extension installed. I'm moving to PHP 7.4 anyway.

Test script:
---------------
The manual is the issue, not the function (as far as I know).
Still, to save you time. :-)

mb_internal_encoding("UTF-8");

$name = "Anthony";

echo $name . "<br>";

$newName = mb_substr($name, 0, 7);

echo $newName . "<br>";

$badName = mb_substr($name, 0, 20);

echo $badName . "<br>";

$badName = mb_substr($name, 20, 20);

echo $badName . "<br>";

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 [2019-12-09 00:11 UTC] requinix@php.net
-Summary: What does mb_substr() return when it fails? +Summary: What do mbstring functions return when they fail? -Package: Documentation problem +Package: mbstring related
 [2019-12-09 00:11 UTC] requinix@php.net 
As with most other PHP functions, if there is some sort of problem then it returns false.

Looks like others don't have this documented either.
 [2019-12-13 19:12 UTC] drtechno at mail dot com 
well, it would be the same as substr() because its the same thing just with multi-byte characters instead of the 7 bit ascii.

so the rules should be:
 Returns the extracted part of string; or FALSE on failure, or an empty string. 

False output example would be subtracting more than the length of the word, and it is being used in a comparative state (ex: if(mb_substr($name, 0, 7)=="y"){ }).
 [2019-12-13 19:36 UTC] drtechno at mail dot com 
Also, I should add and to remind everyone who uses php character filters like substr(), mbsubstr(), htmlentities(), and htmlspecialchars() to always include the coding inline, as sometimes the internal timing will return Null, then either the filter will not work, or will return an error.
like:

mb_substr($name 0, 7, $encoding="UTF-8");

htmlentities($name, $flags=ENT_QUOTES, $encoding="UTF-8");
or
htmlentities($name, ENT_QUOTES, "UTF-8");
 [2021-09-09 16:46 UTC] cmb@php.net
-Status: Open +Status: Not a bug -Assigned To: +Assigned To: cmb
 [2021-09-09 16:46 UTC] cmb@php.net 
> Would you please add what mb_substr() returns when it fails to
> the manual page?

It does not fail if you pass proper input; even invalid character
ranges always produce a string[1].

It only fails, if you pass unsupported input[2], in which case it
doesn't really matter what the function returns since the behavior
is undefined[3], and should never be dealt with in code.  Fix the
erroneous calls instead.

[1] <https://3v4l.org/WUJhX#v730>
[2] <https://3v4l.org/sH51s>
[3] <https://www.php.net/manual/en/functions.internal.php>
 
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