What is the best way to split a string into an array of Unicode characters in PHP?

Question

In PHP, what is the best way to split a string into an array of Unicode characters? If the input is not necessarily UTF-8?

I want to know whether the set of Unicode

Answer 1

If for some reason the regex way isn't enough for you. I once wrote the Zend_Locale_UTF8 which is abandoned but might be helping you if you decide to do it on your own.

In particular have a look at the class Zend_Locale_UTF8_PHP5_String which reads in Unicode strings and to work with them splits them up into single chars(which may consist out of multiple bytes obviously).

EDIT: I just relaized that ZF's svn-browser is down so I copied the important methods for convenience:

/**
 * Returns the UTF-8 code sequence as an array for any given $string.
 *
 * @access protected
 * @param string|integer $string
 * @return array
 */
protected function _decode( $string ) {

    $string     = (string) $string;
    $length     = strlen($string);
    $sequence   = array();

    for ( $i=0; $i<$length; ) {
        $bytes      = $this->_characterBytes($string, $i);
        $ord        = $this->_ord($string, $bytes, $i);

        if ( $ord !== false )
            $sequence[] = $ord;

        if ( $bytes === false )
            $i++;
        else
            $i  += $bytes;
    }

    return $sequence;

}

/**
 * Returns the UTF-8 code of a character.
 *
 * @see http://en.wikipedia.org/wiki/UTF-8#Description
 * @access protected
 * @param string $string
 * @param integer $bytes
 * @param integer $position
 * @return integer
 */
protected function _ord( &$string, $bytes = null, $pos=0 )
{
    if ( is_null($bytes) )
        $bytes = $this->_characterBytes($string);

    if ( strlen($string) >= $bytes ) {

        switch ( $bytes ) {
            case 1:
                return ord($string[$pos]);
                break;

            case 2:
                return  ( (ord($string[$pos])   & 0x1f) << 6 ) +
                        ( (ord($string[$pos+1]) & 0x3f) );
                break;

            case 3:
                return  ( (ord($string[$pos])   & 0xf)  << 12 ) + 
                        ( (ord($string[$pos+1]) & 0x3f) << 6 ) +
                        ( (ord($string[$pos+2]) & 0x3f) );
                break;

            case 4:
                return  ( (ord($string[$pos])   & 0x7)  << 18 ) + 
                        ( (ord($string[$pos+1]) & 0x3f) << 12 ) + 
                        ( (ord($string[$pos+1]) & 0x3f) << 6 ) +
                        ( (ord($string[$pos+2]) & 0x3f) );
                break;

            case 0:
            default:
                return false;
        }
    }

    return false;
}
/**
 * Returns the number of bytes of the $position-th character.
 *
 * @see http://en.wikipedia.org/wiki/UTF-8#Description
 * @access protected
 * @param string $string
 * @param integer $position
 */
protected function _characterBytes( &$string, $position = 0 ) {
    $char       = $string[$position];
    $charVal    = ord($char);

    if ( ($charVal & 0x80) === 0 )
        return 1;

    elseif ( ($charVal & 0xe0) === 0xc0 )
        return 2;

    elseif ( ($charVal & 0xf0) === 0xe0 )
        return 3;

    elseif ( ($charVal & 0xf8) === 0xf0)
        return 4;
    /*
    elseif ( ($charVal & 0xfe) === 0xf8 )
        return 5;
    */

    return false;
}