Either you typed an invisible character (copy/pasted a BOM?) or that slash is a Unicode slash made up of multiple bytes.

If you intend to support multibyte strings and non-ASCII encodings then use mbstring and mb_substr() instead.

Hello requinix@php.net,

I appreciate your attention into the matter.

I know for sure that there are no multibyte strings or invisible characters in my testing. Functions strlen, mb_strlen and mb_detect_encoding return 3, 3 and "ASCII" respectively.

In the mantime, I've just finished configuring PHP 7.2.11 and PHP 7.3.6, as Apache modules, and they both do not exibit this issue with the very same test file and test environment.

The real mistery for me is why specifically PHP 7.2.19 does not want to work as it should. Please note that the issue presents itself only when I run PHP 7.2.19 as an Apache module. The issue does not occur when I run PHP via CMD (php.exe -f script.php).

Is there any specific test or debug information that I can provide to further identify the issue?

I tested it on Windows using the following script:

var_dump(
  substr("/es", 0, 1)
);
var_dump(
  substr("\xEF\xBB\xBF/es", 0, 1)
);

Output:

string(1) "/"
string(1) "�"


In general try using var_dump() on the source string. It will report the byte length, so you will notice invisible characters.

Hello subjective@php.net,

Are your results from running the script with PHP as an Apache module?

I've thoroughly tried over and over again, and no matter what, I always get the wrong results.

var_dump reports <<string(3) "/es">>.

I've been able to pin-point the issue to the OPCache extension. If I simply remove "zend_extension=opcache" from php.ini, everything works as it should.

Please note that I'm experiencing this issue only with PHP 7.2.19 when it is working as an Apache module.

I can use PHP 7.2.11, 5.6.40, 7.3.6, etc., with OPCache enabled and everything works OK in there.

As a final note, what can I do to 'ring' attention to an existing filed bug? It is about this one: https://bugs.php.net/bug.php?id=77014 - at least to know if it is a bug or intended behaviour.

If removing opcache makes your problem go away then this may be a bug after all.

Please run the following variation of your script, and report the
results:

    <?php
    $in = "/es";
    $out = substr($in, 0, 1);
    var_dump(bin2hex($in), bin2hex($out));
    ?>

Hello cmb@php.net,

Results with OPCache on:
string(6) "2f6573" string(2) "ff"

Results with OPCache off:
string(6) "2f6573" string(2) "2f"

I want to check back whether this issue still exists in PHP 7.2.20. The 7.2.19 release had some serious issues with opcache and it may be that this is a side-effect of the same problems.

I confirm that this issue is no longer present in PHP 7.2.20 for my environment.

Thanks for the confirmation! In that case I'm closing this issue...