# RFC: Change the default of $characters in mb_trim function

- Status: Under discussion
- Authors: Yuya Hamada, youkidearitai@gmail.com
- Date: 2024-04-03
- Version: 0.1
- Original: https://wiki.php.net/rfc/mb_trim_change_characters
- Page: https://externals.io/rfc/mb_trim_change_characters
- More for agents: search with https://externals.io/search.md?q={query} · RFCs at https://externals.io/rfc.md · JSON API at https://externals.io/api · documentation at https://externals.io/llms.txt

## Discussions on the mailing list

- [\[DISCUSSION\] Fix mb_trim inaccurate $character](https://externals.io/message/122908.md) — started on 2024-04-03, 7 messages

---

## Introduction

We found a problem with $characters, the second argument of mb\_trim. This RFC will be a proposed solution to that problem.

First, the mbstring\_arginfo.h file output by mbstring.stub.php, which is added by the mb\_trim function, generates UTF-8 strings, which prevents it from compiling with some on Visual C++

<https://github.com/php/php-src/issues/13789>

Next is the problem that $characters in the mb\_trim function cannot be trimmed with other character encodings with the default.

<https://github.com/php/php-src/issues/13815>

Putting all these together, we create this RFC that $characters in mb\_trim is more appropriate to be null.

## Proposal

Change the default of $characters in mb\_trim, mb\_ltrim and mb\_rtrim functions

```
function mb_trim(string $string, ?string $characters = null, ?string $encoding = null): string
```

```
function mb_ltrim(string $string, ?string $characters = null, ?string $encoding = null): string
```

```
function mb_rtrim(string $string, ?string $characters = null, ?string $encoding = null): string
```

If $characters is null, the following characters are trimmed by default.

Here's the list of characters trimmed:

Same as trim:

```
U+0020 SPACE (also in Separator category)
U+0009 \t
U+000A \n
U+000B \v
U+000D \r
```

not removed in trim(), probably it wasn't common enough, but ok for mb\_trim

```
U+000C \f
```

Removed in trim, but not included in regex \\s

```
U+0000 \0
```

whole Separator Z category (20 codepoints) covered by regex \\s:

```
U+0020 SPACE
U+00A0 NO-BREAK SPACE
U+1680 OGHAM SPACE MARK
U+2000 EN QUAD
U+2001 EM QUAD
U+2002 EN SPACE
U+2003 EM SPACE
U+2004 THREE-PER-EM SPACE
U+2005 FOUR-PER-EM SPACE
U+2006 SIX-PER-EM SPACE
U+2007 FIGURE SPACE
U+2008 PUNCTUATION SPACE
U+2009 THIN SPACE
U+200A HAIR SPACE
U+2028 LINE SEPARATOR
U+2029 PARAGRAPH SEPARATOR
U+202F NARROW NO-BREAK SPACE
U+205F MEDIUM MATHEMATICAL SPACE
U+3000 IDEOGRAPHIC SPACE
```

Other symbols (included in regex \\s):

```
U+0085 NEXT LINE (NEL)
U+180E MONGOLIAN VOWEL SEPARATOR
```

## Backward Incompatible Changes

This could break a function existing in userland with the same name.

## Proposed PHP Version(s)

PHP 8.4

## RFC Impact

### To SAPIs

To SAPIs Will add the aforementioned functions to all PHP environments.

### To Existing Extensions

Fixes mb\_trim(), mb\_ltrim() and mb\_rtrim() to the mbstring extension.

### To Opcache

No effect.

### New Constants

No new constants.

### php.ini Defaults

No changed php.ini settings.

## Open Issues

- <https://github.com/php/php-src/issues/13789>
- <https://github.com/php/php-src/issues/13815>

## Future Scope

This section details areas where the feature might be improved in future, but that are not currently proposed in this RFC.

## Proposed Voting Choices

Include these so readers know where you are heading and can discuss the proposed voting options.

## Implementation

- <https://github.com/php/php-src/pull/13820>

## References

[https://wiki.php.net/rfc/mb\_trim](https://externals.io/rfc/mb_trim)

## Rejected Features

Keep this updated with features that were discussed on the mail lists.