php 中session有关问题 isset（）不能判断

php 中session问题 isset（）不能判断
login.php
session_start();
include_once 'fuctions.php';
$account=$_REQUEST["account"];
  $password=$_REQUEST["password"];
  $con = connectDB();
  $query="select * from im where account='".$account."' and password='".$password."';";
  $result=mysql_query($query);
  if($row=mysql_fetch_array($result)){
  echo("true");
  $_SESSION['$row["id"]']=true;
  }
  else{
  echo("false");
  }
  mysql_close($con);
?>

contact.php
session_start();
include_once 'fuctions.php';
$con = connectDB();
$query = "select * from im";
$result = mysql_query($query);
$count = 0;
while ($row = mysql_fetch_array($result)) {
  $contact[$count] = array("id" => $row["id"], "name" => $row["name"], "group" => $row["group"], "phone" => $row["phone"],"online"=>1);
  $count++;
}
for($i=0;$i   if(!isset($_SESSION['$contact[$i]["id"]'])){
$contact[$i]["online"]=0;
}
}
foreach ($contact as $key => $array) {
  if (is_array($array)){
  foreach ($array as $key => $value) {
  echo($key."=>".$value." ");
  }
  }
}
$json=array();
for ($i = 0; $i   ["group"],"phone"=>$contact[$i]["phone"]);
}
mysql_close($con);
?>

为什么每次isset($_SESSION['$contact[$i]["id"]'])都判断不出来呢？

------解决方案--------------------

C/C++ code

[User:root Time:12:01:13 Path:/home/liangdong/php]$ php dot.php 
Array
(
    [$b] => 1
)
[User:root Time:12:01:16 Path:/home/liangdong/php]$ cat dot.php 
<?php $a['$b'] = 1;
print_r($a);
?>
[User:root Time:12:01:18 Path:/home/liangdong/php]$
<br><font color="#e78608">------解决方案--------------------</font><br>把<br>$_SESSION['$row["id"]']=true;和isset($_SESSION['$contact[$i]["id"]'])<br>改成<br>$_SESSION["$row['id']"]=true;和isset($_SESSION["$contact[$i]['id']"])<br><br><br>引号用反了，这种IDE应该会提示的吧<br><br><br>
<br><font color="#e78608">------解决方案--------------------</font><br>if(!isset($_SESSION[$contact[$i]["id"]])){<br> $contact[$i]["online"]=0;<br>}<br>去掉那对倒霉的单引号
<br><font color="#e78608">------解决方案--------------------</font><br>$_SESSION[$row['id']]=true;<br>数组内键值不用加引号<br> <div class="clear">
                 
              
              
        
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