PHP实现mb_strlen

UTF-8一个汉字占2个字符，GBK一个汉字占3个字符，ASCII码最大能表示到十进制128，16进制0x80，所以当某个字符当ASCII码超出最大值128时，则代表中文汉字，再根据编码跳过对应字节数即可

function mbstrlen($str, $type = 'utf-8')
{
	$len = strlen($str);
	
	if ($len <= 0)
	{
		return 0;
	}
	
    $count  = 0;
    $step = $type == 'utf-8' ? 2 : 3;
	
	for ($i = 0; $i < $len; $i++)
	{
		$count++;
		if (ord($str{$i}) >= 128)
		{
			$i += $step;
		}
	}
	return $count;
}

$str = '程序猿';
echo strlen($str) . "\n";
echo mbstrlen($str) . "\n";
$str = mb_convert_encoding($str, 'utf-8', 'gbk');;
echo mbstrlen($str, 'gbk') . "\n";

[Running] php "/Users/why/Desktop/php/shmop.php"
9
3
3

[Done] exited with code=0 in 0.288 seconds