php emoji表情转换

function emoji2str($str){     
    $strEncode = '';       
    $length = mb_strlen($str,'utf-8');       
    for ($i=0; $i < $length; $i++) {         
        $_tmpStr = mb_substr($str,$i,1,'utf-8');         
        if(strlen($_tmpStr) >= 4){             
            $strEncode .= '[[EMOJI:'.rawurlencode($_tmpStr);         
        }else{             
            $strEncode .= $_tmpStr;        
        }     
    }     
    return $strEncode; 
}

/* 读数据后重新转换成emoji返回 */ 
function str2emoji($str){     
    $str_arr = explode("[[EMOJI:", $str);     
    $new_str = "";       
    foreach ($str_arr as $key => $val){         
        $new_str .= rawurldecode($val);     
    }       
    return $new_str; 
}