PHP中英数字混排字符串的截取

function smssubstr($string, $length) {
if(strlen($string) <= $length) {
return $string;
}
$strcut = '';
for($i = 0; $i < $length; $i++) {
$strcut .= ord($string[$i]) > 127 ? $string[$i].$string[++$i] : $string[$i];
}
return $strcut;
}

for($i=1; $i<=$smsnum; $i++){
${'smscontent'.$i} = smssubstr($message,$smsper);
$message = str_replace(${'smscontent'.$i},"",$message);
}