为什么此查询脚本返回致命错误？

Question

I get a fatal error on executing the query below:

$stmt = $db->query('SELECT * FROM comments LIMIT 50');
    while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
        echo $result['name'] . ':' . strip_tags($result['message']);
    }

Returns:

  Fatal error: Call to a member function query() on a non-object

I set my $db like this:

try {$db = new PDO('mysql:host=localhost;dbname=database', 'username', 'password');}
catch(PDOException $e) {echo $e->getMessage();}

Does anyone know what causes this error?

Answer 1

You are not getting an error because of the execution of the query. The query in fact will never try to execute

This error -

Fatal error: Call to a member function query() on a non-object

tells you that $db is not an object.

Either it was never instantiated, or it was instantiated within a different scope.

Answer 2

$db has not been properly initialized in the scope you are using it.

You might want to try putting a global $db; before both of them to see if it is a scope problem.

global $db;
try {$db = new PDO('mysql:host=localhost;dbname=database', 'username', 'password');}
catch(PDOException $e) {echo $e->getMessage();}

global $db;
$stmt = $db->query('SELECT * FROM comments LIMIT 50');
    while ($result = $stmt->fetch(PDO::FETCH_ASSOC)) {
        echo $result['name'] . ':' . strip_tags($result['message']);
    }