L'ID utilisateur n'est pas défini

Question

Ok J'essaye de lister tous les utilisateurs dans mysql et cela fonctionne mais quand j'ajoute un profile.php?id= j'obtiens mon code d'autre L'ID d'utilisateur n'est pas défini. comment puis-je le définir afin qu'il ne dise pas L'ID utilisateur n'est pas défini. voici mon code:

<?php 
include('config/db.php'); 
?> 
<?php 
$host="localhost"; // Host name 
$username="root"; // Mysql username 
$password="password"; // Mysql password 
$db_name="login"; // Database name 
$tbl_name="users"; // Table name 
mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
mysql_select_db("$db_name")or die("cannot select DB"); 
//We check if the members ID is defined 
if(isset($_GET['user_id'])) 
{ 
$id = intval($_GET['user_id']); 
//We check if the user exists 
$dn = mysql_query('select user_name, user_email from users where  user_id="'.$id.'"'); 
if(mysql_num_rows($dn)>0) 
{ 
    $dnn = mysql_fetch_array($dn); 
    //We display the user datas 
?> 
This is the profile of "<?php echo htmlentities($dnn['user_name']); ?>" : 
<table style="width:500px;"> 
<tr> 
    <td><?php 
if($dnn['avatar']!='') 
{ 
echo '<img src="'.htmlentities($dnn['avatar'], ENT_QUOTES, 'UTF-8').'" alt="Avatar"  style="max-width:100px;max-height:100px;" />'; 
} 
else 
{ 
echo 'This user dont have an avatar.'; 
} 
?></td> 
    <td class="left"><h1><?php echo htmlentities($dnn['user_name'], ENT_QUOTES, 'UTF- 8'); ?></h1> 
    Email: <?php echo htmlentities($dnn['user_email'], ENT_QUOTES, 'UTF-8'); ?><br /> 
    This user joined the website on <?php echo date('Y/m/d',$dnn['signup_date']); ?> </td> 
</tr> 
</table> 
<?php 
} 
else 
{ 
    echo 'This user dont exists.'; 
} 
} 
else 
{ 
echo 'The user ID is not defined.'; 
} 
?> 
this is the users.php 
    <?php 
//We get the IDs, usernames and emails of members 
$req = mysql_query('SELECT `user_id`, `user_name`, `user_email`, `user_sign_up_date` FROM `users`'); 
while($dnn = mysql_fetch_array($req)) 
{ 
?> 
<tr> 
    <td class="left"><?php echo $dnn['user_id']; ?></td> 
    <td class="left"><a href="profile.php?<?php echo $dnn['user_id']; ?>"><?php echo ($dnn['user_name']); ?></a></td> 
    <td class="left"><?php echo($dnn['user_email']); ?></td> 
</tr> 
<?php 
} 
?> 

Answer 1

requête Vous retourne faux sur la ligne suivante

$dn = mysql_query('select user_name, user_email from users where user_id="'.$id.'"'); 

Vous aurez besoin de savoir pourquoi, vous ne devriez pas tenter quoi que ce soit jusqu'à ce qu'il retourne vrai:

$sql = sprintf("SELECT user_name, user_email FROM users WHERE user_id = %s", 
       mysql_real_escape_string($id)); 
$dn = mysql_query($sql); 

if(!$dn){ 
    echo "mysql_query() failed"; 
    exit(); 
}