Fix PHP8.2 str_split function returns empty arrays for empty strings

[HuongNV13]

In PHP 8.2, the str_split function will returns empty arrays for empty strings.
See: https://php.watch/versions/8.2/str_split-empty-string-empty-array

We can use mb_str_split() instead

[CLAassistant]

All committers have signed the CLA.

[fooman]

Unfortunately mb_str_split() was only introduced in php7.4 which will make swapping this out trickier.

[williamdes]

Unfortunately mb_str_split() was only introduced in php7.4 which will make swapping this out trickier.

Thanks for the hint!
Okay, some code needs to be added and use PHP_MAJOR_VERSION const and it's friends

[williamdes]

or maybe just function_exists()

[HuongNV13]

Thanks, everyone.
I have updated the code to use function_exists() to use the correct method.

[MacGritsch]

I think this is not a valid fix as mb_str_split() behaves the same way as str_split() in PHP 8.2 and above.
So why dont check if its an empty string (and if its needed in that case).
Otherwise you could also write a function str_split_old() which returns array('') if the input string is empty.

[survik1]

Looks like incorrect indentation, project uses tabs while this code introduces spaces. Same can be said about all other new lines in this MR.

[nicolaasuni]

Please try to resolve the conflicts.
Could you please instead create a wrapper function in tcpdf_static.php?

[HuongNV13]

Hi Nicola,
Sorry for the late reply, I was busy with my project.
I will update the patch soon.

Thanks,

[nicolaasuni]

Hi,
If this is still an issue please try to create a wrapper function in tcpdf_static.php.
Alternatively please consider using the new tc-lib-pdf if you don't need HTML/CSS/SVG/Javascript features that are still in development.

[williamdes]

If this is still an issue please try to create a wrapper function in tcpdf_static.php.

Very good idead
@HuongNV13 can you do it ?

This PR should be marked as draft for now

[nicolaasuni]

Thank you very much, @HuongNV13, for tracking down the PHP 8.2 str_split() behaviour change and proposing a fix - it is genuinely appreciated.

TCPDF 6 is now deprecated and no further changes will be merged into this repository. Please see the pinned issue Thank You - and the Future of TCPDF for the full explanation and the path forward.

The empty-string edge case you identified is handled correctly in the modern PHP string utilities used by tc-lib-pdf. If you encounter a related issue there, feel free to open a PR or issue in that repository. If you need any help adapting your fix to the new library, please open a discussion and I will do my best to assist.

I am leaving this PR open in case you or anyone else wishes to continue the discussion, but it is unlikely that this PR will ever be merged.

Thank you again for your patience and understanding.