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strrchr with needle with multiple characters

php.internals

Vincent Langlet

1 year ago

I was today old when I discovered the big difference between strchr and
strrchr in the way they handle needle with multiple characters.

It's explained in the doc https://www.php.net/manual/en/function.strrchr.php
- If needle contains more than one character, only the first is used. This
behavior is different from that of strstr()
<https://www.php.net/manual/en/function.strstr.php>.

You can see an example https://3v4l.org/7j5ab

I feel like this behavior has no benefit (if I want to look for the first
character, I can pass `substr($needle, 0, 1)` instead) and is just
error-prone.

Is there a reason for such behavior ? Would it be easy to change it (I have
no knowledge at all in C and in the existing PHP code) ?

David CARLIER

1 year ago

Hi,

On Mon, 2 Sept 2024 at 12:20, Vincent Langlet <misterdeviling@gmail.com>
wrote:

> I was today old when I discovered the big difference between strchr and
> strrchr in the way they handle needle with multiple characters.
>
> It's explained in the doc
> https://www.php.net/manual/en/function.strrchr.php
> - If needle contains more than one character, only the first is used.
> This behavior is different from that of strstr()
> <https://www.php.net/manual/en/function.strstr.php>.
>
> You can see an example https://3v4l.org/7j5ab
>
> I feel like this behavior has no benefit (if I want to look for the first
> character, I can pass `substr($needle, 0, 1)` instead) and is just
> error-prone.
>
> Is there a reason for such behavior ? Would it be easy to change it (I
> have no knowledge at all in C and in the existing PHP code) ?
>

It is a bit ambiguous, I'll give you that, albeit you can pass a string to
str(r)chr only the first character is used, these are literally similar to
their C counterparts

https://www.tutorialspoint.com/c_standard_library/c_function_strchr.htm
https://www.tutorialspoint.com/c_standard_library/c_function_strrchr.htm

see the second argument handles one character at a time.

Cheers.

Christoph Becker

1 year ago

On 02.09.2024 at 13:17, Vincent Langlet wrote:

> I was today old when I discovered the big difference between strchr and
> strrchr in the way they handle needle with multiple characters.
>
> It's explained in the doc https://www.php.net/manual/en/function.strrchr.php
> - If needle contains more than one character, only the first is used. This
> behavior is different from that of strstr()
> <https://www.php.net/manual/en/function.strstr.php>.
>
> You can see an example https://3v4l.org/7j5ab
>
> I feel like this behavior has no benefit (if I want to look for the first
> character, I can pass `substr($needle, 0, 1)` instead) and is just
> error-prone.
>
> Is there a reason for such behavior ? Would it be easy to change it (I have
> no knowledge at all in C and in the existing PHP code) ?

strchr() is an alias of strstr(), and I would always use the latter
name, because strchr() is indeed confusing.  Anyhow, strstr() is very
useful in C, but not so much in PHP, since in PHP it will always
allocate a new string, even if that is not needed.

Now, comparing strstr() and strrchr() is of course still possible, but
different behavior is less astonishing.  Of course, strrchr() could warn
or even throw if $needle has more than one character, but that may
unnecessarily break code for a small benefit.

Christoph

Tim Düsterhus

1 year ago

Hi

Am 2024-09-02 15:24, schrieb Christoph M. Becker:

> Now, comparing strstr() and strrchr() is of course still possible, but
> different behavior is less astonishing.  Of course, strrchr() could
> warn
> or even throw if $needle has more than one character, but that may
> unnecessarily break code for a small benefit.

I would expect that passing more than one character to `strrchr()` is
very likely to be an accident or a misunderstanding of how the function
behaves and thus already broken. A warning would just visibly point out
that it is broken, instead of it silently behaving in a manner that
diverges from the user's expectations (possibly unpredictably if the
function is working on untrusted / user input).

If the function would be newly introduced, I'd make it an error to pass
more than one character, but given that the function already exists, I'd
say that pointing out such mistakes is exactly what the Warning / Notice
facility is for.

Best regards
Tim Düsterhus