Why I Am Getting Cannot Pass Parameter 2 by Reference Error When I Am Using Bindparam With a Constant Value

Why I am getting Cannot pass parameter 2 by reference error when I am using bindParam with a constant value?

You need to use bindValue, not bindParam

bindParam takes a variable by reference, and doesn't pull in a value at the time of calling bindParam. I found this in a comment on the PHP docs:

bindValue(':param', null, PDO::PARAM_INT);

P.S. You may be tempted to do this bindValue(':param', null, PDO::PARAM_NULL); but it did not work for everybody (thank you Will Shaver for reporting.)

Cannot pass parameter 2 by reference error in php PDO

It expects the second paramter to be a variable which can be passed by reference. Assuming $stmt1is a PDO statement then, as the docs for bindparam say

Unlike PDOStatement::bindValue(), the variable is bound as a reference
and will only be evaluated at the time that PDOStatement::execute() is
called.

Your second param is an expression ($_SESSION['quantity'.$i] * $_SESSION['price'.$i]) not a variable. Since you appear to want to evaluate the exptression now, I guess you should used bindValue() instead.

Cannot pass parameter 2 by reference - PDO

The bindParam() method binds the parameter to a variable. Strings are what are called constants.

In order to make this work you have to pass a variable to the method, like this:

// Prepare the statement
$stmt = $dbh->prepare("INSERT INTO messages (message, sender, key) VALUES (:message, :sender, :key)");

// Bind variables to the parameters
$stmt->bindParam(':message', $message);
$stmt->bindParam(':sender', $sender);
$stmt->bindParam(':key', $key);

// Give the bound variables a value
$message = 'The message...';
$sender = 'Smith';
$key = 'Test-Key';

// And then execute the statement
$stmt->execute();

PHP error: Cannot pass parameter 2 by reference

The error means that the 2nd argument is expected to be a reference to a variable.

Since you are not handing a variable but an integer of value 0, it generates said error.

To circumvent this do:

$a = 0;
$update->bind_param("is", $a, $selectedDate);  //LINE 13

In case you want to understand what is happening, as opposed to just fixing your Fatal error, read this: http://php.net/manual/en/language.references.pass.php

Fatal error: Uncaught Error: Cannot pass parameter 2 by reference PDO

The second argument to bindParam is passed by reference and therefore cannot be a literal it must be be a variable.

You also have an error in the Query syntax which I fixed, although I dont know the column name to use, please change that before attempting to use this code.

function buscador($DB,$categoria_id,$buscado){
    $productos = NULL;
    $sql = "SELECT * from producto WHERE categoria_id = ? AND othercol LIKE ?";
    $stmt = $DB->prepare($sql);

    $p2 = '%' . $buscado . '%';

    $stmt->bindParam(1,$categoria_id,PDO::PARAM_STR);
    $stmt->bindParam(2,$p2,PDO::PARAM_STR);
    $stmt->execute();
    $productos = $stmt->fetchAll();

    return $productos;
}

Cannot pass parameter by reference in MySQLi

'1' cannot be passed by reference because it's not a variable but a literal. You need to create a variable with mentioned value and bind it instead because bind_param() function expects variables passed by reference.

Can't pass a constant variable by reference with $stmt->bind_param()?

Quite simply, it's because you can't pass a constant by reference, and there would be no point in doing so, as it is immutable. Constants, by the way, are not variables; it's right there in the name.

When using PDO::bindParam my query returns no results

Try using bindValue instead of bindParam. In the user submitted notes in the PHP manual (php.net/manual/en/pdostatement.bindvalue.php) there is a note about bindParam passing by reference, whereas bindValue doesn't.

PDO integer nullable value issue

You need to use bindValue like below:-

$Query =$db->prepare("UPDATE TblUsers
SET Age = :age
WHERE
 IsActive=1 ")
$Query->bindValue(':age', $a, PDO::PARAM_INT);
$Query->execute();

bindParam takes a variable, to reference, and doesn't pull in a value at the time of calling bindParam.

Referecne:-How do I insert NULL values using PDO?

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