Why Does `bindParam` Fail with Constants and How Can I Use `bindValue` Instead?

Resolving "Cannot pass parameter 2 by reference" Error When Using bindParam with Constants

In your code snippet, you encounter the error "Cannot pass parameter 2 by reference" when attempting to use bindParam with a constant value (e.g., PDO::PARAM_NULL). This error occurs because bindParam requires a variable to bind to, while you are passing a constant value.

To resolve this issue, you need to use bindValue instead of bindParam. bindValue binds a value directly to the parameter, rather than a variable. Here's the corrected code:

try {
    $dbh = new PDO('mysql:dbname=' . DB . ';host=' . HOST, USER, PASS);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $dbh->setAttribute(PDO::MYSQL_ATTR_INIT_COMMAND, "SET NAMES 'utf8'");
}
catch(PDOException $e)
{
    ...
}
$stmt = $dbh->prepare('INSERT INTO table(v1, v2, ...) VALUES(:v1, :v2, ...)');
$stmt->bindValue(':v1', null, PDO::PARAM_INT); // Using bindValue with null and explicit type

Note: You may be tempted to use bindValue(':param', null, PDO::PARAM_NULL), but this approach does not always work. Instead, it is recommended to use the explicit type, such as PDO::PARAM_INT in this example.

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