php - Convert a String into an Array of Characters - multi-byte

Question

Assuming that in 2019 every solution which is not UNICODE-safe is wrong. What is the best way to convert a string to array of UNICODE characters in PHP?

Obviously this means that accessing the bytes with the brace syntax is wrong, as well as using str_split:

$arr = str_split($text);

From sample input like:

$string = '先ée?€??????? ????????';

I expect:

array(16) {


[0]=>
  string(3) "先"
  [1]=>
  string(2) "é"
  [2]=>
  string(1) "e"
  [3]=>
  string(2) "?"
  [4]=>
  string(3) "€"
  [5]=>
  string(4) "??"
  [6]=>
  string(4) "??"
  [7]=>
  string(4) "??"
  [8]=>
  string(3) "?"
  [9]=>
  string(1) " "
  [10]=>
  string(4) "??"
  [11]=>
  string(3) "?"
  [12]=>
  string(3) "?"
  [13]=>
  string(3) "?"
  [14]=>
  string(3) "?"
  [15]=>
  string(4) "??"
}

Answer 1

Just pass an empty pattern with the PREG_SPLIT_NO_EMPTY flag. Otherwise, you can write a pattern with X (unicode dot) and K (restart fullstring match). I'll include a mb_split() call and a preg_match_all() call for completeness.

Code: (Demo)

$string='先秦兩漢';
var_export(preg_split('~~u', $string, 0, PREG_SPLIT_NO_EMPTY));
echo "
---
";
var_export(preg_split('~XK~u', $string, 0, PREG_SPLIT_NO_EMPTY));
echo "
---
";
var_export(preg_split('~XK(?!$)~u', $string));
echo "
---
";
var_export(mb_split('XK(?!$)', $string));
echo "
---
";
var_export(preg_match_all('~X~u', $string, $out) ? $out[0] : []);

All produce::

array (
  0 => '先',
  1 => '秦',
  2 => '兩',
  3 => '漢',
)

From https://www.regular-expressions.info/unicode.html:

How to Match a Single Unicode Grapheme

Matching a single grapheme, whether it's encoded as a single code point, or as multiple code points using combining marks, is easy in Perl, PCRE, PHP, Boost, Ruby 2.0, Java 9, and the Just Great Software applications: simply use X.

You can consider X the Unicode version of the dot. There is one difference, though: X always matches line break characters, whereas the dot does not match line break characters unless you enable the dot matches newline matching mode.

---

UPDATE, DHarman has brought to my attention that mb_str_split() is now available from PHP7.4.

The default length parameter of the new function is 1, so the length parameter can be omitted for this case.

https://wiki.php.net/rfc/mb_str_split

Dharman's demo: https://3v4l.org/M85Fi/rfc#output