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(PHP 5 >= 5.3.0, PECL intl >= 1.0.0)
grapheme_extract — Function to extract a sequence of default grapheme clusters from a text buffer, which must be encoded in UTF-8.
过程化风格
$haystack 
   ,  int $size 
   [,  int $extract_type 
   [,  int $start  = 0 
   [,  int &$next 
  ]]] )Function to extract a sequence of default grapheme clusters from a text buffer, which must be encoded in UTF-8.
haystack String to search.
size Maximum number items - based on the $extract_type - to return.
extract_type Defines the type of units referred to by the $size parameter:
start Starting position in $haystack in bytes - if given, it must be zero or a positive value that is less than or equal to the length of $haystack in bytes. If $start does not point to the first byte of a UTF-8 character, the start position is moved to the next character boundary.
next Reference to a value that will be set to the next starting position. When the call returns, this may point to the first byte position past the end of the string.
A string starting at offset $start and ending on a default grapheme cluster boundary that conforms to the $size and $extract_type specified.
Example #1 grapheme_extract() example
  <?php
$char_a_ring_nfd  =  "a\xCC\x8A" ;   // 'LATIN SMALL LETTER A WITH RING ABOVE' (U+00E5) normalization form "D"
 $char_o_diaeresis_nfd  =  "o\xCC\x88" ;  // 'LATIN SMALL LETTER O WITH DIAERESIS' (U+00F6) normalization form "D"
 print  urlencode ( grapheme_extract (  $char_a_ring_nfd  .  $char_o_diaeresis_nfd ,  1 ,  GRAPHEME_EXTR_COUNT ,  2 ));
 ?>   以上例程会输出:
o%CC%88
[#1] AJH [2011-07-12 16:37:58]
Here's how to use grapheme_extract() to loop across a UTF-8 string character by character.
<?php
$str = "?abc?????";
// if the previous line didn't come through, the string contained:
//U+0633,U+0061,U+0062,U+0063,U+0915,U+2019,U+2026
$n = 0;
for (    $start = 0, $next = 0, $maxbytes = strlen($str), $c = '';
        $start < $maxbytes;
        $c = grapheme_extract($str, 1, GRAPHEME_EXTR_MAXCHARS , ($start = $next), $next)
    )
{
    if (empty($c))
        continue;
    echo "This utf8 character is " . strlen($c) . " bytes long and its first byte is " . ord($c[0]) . "\n";
    $n++;
}
echo "$n UTF-8 characters in a string of $maxbytes bytes!\n";
// Should print: 7 UTF8 characters in a string of 14 bytes!
?>