从一个不错的留言本弄的mysql数据库操作类，初学php的朋友可以参考下

<?php 
class mysql{ 
    var $querynum = 0; 
    function connect($dbhost, $dbuser, $dbpw, $dbname = '',$dbcharset='') { 
        if(!@mysql_connect($dbhost, $dbuser, $dbpw)) { 
            $this->show('Can not connect to MySQL server'); 
            return false; 
        } 
        if($dbname) { 
            $this->select_db($dbname); 
        } 
        if($this->version() > '4.1' && $dbcharset) { 
            $this->query("SET NAMES '".$dbcharset."'"); 
        } 
        return true; 
    } 

    function select_db($dbname) { 
        return mysql_select_db($dbname); 
    } 

    function fetch_array($query, $result_type = MYSQL_ASSOC) { 
        return @mysql_fetch_array($query, $result_type); 
    } 

    function query($sql, $type = '') { 
        if(!($query = mysql_query($sql))) $this->show('MySQL Query Error', $sql); 
        $this->querynum++; 
        return $query; 
    } 

    function affected_rows() { 
        return mysql_affected_rows(); 
    } 

    function result($query, $row) { 
        return mysql_result($query, $row); 
    } 

    function num_rows($query) { 
        return @mysql_num_rows($query); 
    } 

    function num_fields($query) { 
        return mysql_num_fields($query); 
    } 

    function free_result($query) { 
        return mysql_free_result($query); 
    } 

    function insert_id() { 
        return mysql_insert_id(); 
    } 

    function fetch_row($query) { 
        return mysql_fetch_row($query); 
    } 

    function version() { 
        return mysql_get_server_info(); 
    } 

    function close() { 
        return mysql_close(); 
    } 

    function error() { 
        return mysql_error(); 
    } 

    function show($message = '', $sql = '') { 
        if(!$sql) echo $message; 
        else echo $message.'<br>'.$sql.'<br>'.$this->error(); 
    } 
} 

class page extends mysql{ 
    function pagination($sql,$maxnum,$page,$maxpages,$pagepre,$ext=''){ 
        global $sum,$stail,$link,$lmid,$ltail,$curpage;//$ext='&class=3' 
        $SELF = $_SERVER['PHP_SELF']; 

        $query = $this->query($sql); 
        $rows = $this->fetch_array($query,MYSQL_NUM); 
        $totalrows = $rows[0]; 

        $totalpages = ceil($totalrows/$maxnum); 
        $startnum = ($page - 1)*$maxnum; 
        $string = $sum.$totalrows.$stail.$sum.$page."/".$totalpages.$stail; 

        if($page != 1){ 
            $string .= $link.$SELF."?page=1".$ext.$lmid."|‹".$ltail; 
            $string .=  $link.$SELF.'?page='.($page - 1).$ext.$lmid."‹‹".$ltail; 
        } 

        if($maxpages>=$totalpages){ 
            $pgstart = 1;$pgend = $totalpages; 
        } 
        elseif(($page-$pagepre-1+$maxpages)>$totalpages){ 
            $pgstart = $totalpages - $maxpages + 1; 
            $pgend = $totalpages; 
        } 
        else{ 
            $pgstart=(($page<=$pagepre)?1:($page-$pagepre)); 
            $pgend=(($pgstart==1)?$maxpages:($pgstart+$maxpages-1)); 
        } 

        for($pg=$pgstart;$pg<=$pgend;$pg++){ 
            if($pg == $page){ 
                $string .=  $curpage.$SELF."?page=".$pg.$ext.$lmid.$pg.$ltail; 
            } 
            else $string .=  $link.$SELF."?page=".$pg.$ext.$lmid.$pg.$ltail; 
        } 

        if($page != $totalpages){ 
            $string .=  $link.$SELF.'?page='.($page + 1).$ext.$lmid."››".$ltail; 
            $string .=  $link.$SELF.'?page='.$totalpages.$ext.$lmid."›|".$ltail; 
        } 
        return $string; 
    } 
} 

function html($str,$allowhtml=0){ 
    $str = get_magic_quotes_gpc()?$str:addslashes($str); 
    if(!$allowhtml){$str = htmlspecialchars($str);} 
    return $str; 
} 

function dehtml($str,$allowhtml=0){ 
    $str = stripslashes($str); 
    if(!$allowhtml){$str = nl2br($str);} 
    return $str; 
} 

function deip($str){ 
    $arr = explode('.',$str); 
    $str = $arr[0].'.'.$arr[1].'.'.$arr[2].'.*'; 
    return $str; 
} 

function setting($login=false){ 
    global $db,$mydbpre; 
    if($login) $sql = "select * from {$mydbpre}setting"; 
    else $sql = "select * from {$mydbpre}setting where keyword != 'username' and keyword != 'password'"; 
    $query = $db->query($sql); 
    while($row = $db->fetch_array($query)){ 
        $arr[$row['keyword']] = $row['val']; 
        if($row['keyword'] == 'name') $arr['title'] = $row['val'].' - Powered by PHPfans'; 
    } 
    return $arr; 
} 

function checkcontent($content){ 
    global $db,$mydbpre,$mearr; 
    $arrword = $arrip = array(); 
    $sql = "select * from {$mydbpre}ban where b_type != 0"; 
    $query = $db->query($sql); 
    while($row = $db->fetch_array($query)){ 
        if($row['b_type'] == 1) $arrword[] = $row['b_val']; 
        elseif($row['b_type'] == 2) $arrip[] = $row['b_reval']; 
    } 
    foreach($arrip as $value){ 
        $value = preg_quote($value,'/'); 
        $value = str_replace('\*','\d{1,3}',$value); 
        if(preg_match('/^('.$value.')$/',$_SERVER['REMOTE_ADDR'])){ 
            showmessage($mearr[8],'index.php'); 
        } 
    } 
    foreach($arrword as $val){ 
        $val = preg_quote($val,'/'); 
        if(preg_match('/'.$val.'/',$content)){ 
            showmessage($mearr[7],'index.php'); 
        } 
    } 
} 

function replaceword($content){ 
    global $db,$mydbpre; 
    $sql = "select * from {$mydbpre}ban where b_type = 0"; 
    $query = $db->query($sql); 
    while($row = $db->fetch_array($query)){ 
        $content = str_replace($row['b_val'],$row['b_reval'],$content); 
    } 
    return $content; 
} 

function showadmin($message,$referer=''){ 
    $str = ''; 
    if($referer != '') $str .= '<meta http-equiv="refresh" content="2;URL='.$referer.'" />'; 
    $str .= ' 
  <table width="45%" align="center" style="border:1px solid #eeeeee; margin-top:50px;"> 
  <tr bgcolor="#CCCCCC"> 
    <td height="25">信息提示</td> 
  </tr> 
  <tr align="center"> 
    <td style="padding:10px 0 10px 0">'.$message; 
    if($referer != '') $str .= '<br /> 
  <br /> 
  <a href="'.$referer.'">如果你的页面没有跳转,请点这里</a>'; 

    $str .= ' 
  </td> 
  </tr> 
  </table>'; 
    echo $str; 
    exit; 
} 

function showmessage($message,$referer=''){ 
    global $setting,$db; 
    $start = gettime(); 
    echo <<<EOT 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> 
<html> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=gbk" /> 
<title>php爱好者留言簿_提示信息</title> 
<link type="text/css" href="guest.css" rel="stylesheet"> 
EOT; 
    if($referer != '') echo '<meta http-equiv="Refresh" content="2;URL='.$referer.'" />'; 
    echo <<<EOT 
</head> 
<body> 
<center> 
EOT; 
    require_once('header.html'); 
    echo <<<EOT 
<div class="message"> 
<h1>php爱好者留言簿 提示信息</h1> 
{$message} 
EOT; 
    if($referer != ''){ 
        echo <<<EOT 
<br /> 
<a href="{$referer}">如果您的浏览器没有自动跳转，请点击这里</a> 
</div> 
EOT; 
} 
require_once('footer.html'); 
echo <<<EOT 
</center> 
</body> 
</html> 
EOT; 
exit; 
} 

function gettime() 
{ 
    $t = explode(" ",microtime()); 
    return $t[1] + $t[0]; 
} 

function checklogin($exit=true){ 
    if(!isset($_COOKIE['islogin']) || $_COOKIE['islogin'] != 1){ 
        if($exit) { 
            echo "请先登陆，谢谢。"; 
            exit; 
        } 
    } 
    else setcookie('islogin',1,time()+60*20); 
} 
?>