What does the PHP error message “Notice: Use of undefined constant” mean?

Question

PHP is writing this error in the logs: \"Notice: Use of undefined constant\".

Error in logs:

PHP Notice:  Use of undefined constant          


        

Answer 1

you probably forgot to use "".

For exemple:

$_array[text] = $_var;

change to:

$_array["text"] = $_var;

Answer 2

You missed putting single quotes around your array keys:

$_POST[email]

should be:

$_POST['email']

Answer 3

Insert single quotes.

Example

$department = mysql_real_escape_string($_POST['department']);
$name = mysql_real_escape_string($_POST['name']);
$email = mysql_real_escape_string($_POST['email']);
$message = mysql_real_escape_string($_POST['message']); 

Answer 4

The correct way of using post variables is

<?php

$department = $_POST['department'];

?>

Use single quotation(')

Answer 5

You should quote your array keys:

$department = mysql_real_escape_string($_POST['department']);
$name = mysql_real_escape_string($_POST['name']);
$email = mysql_real_escape_string($_POST['email']);
$message = mysql_real_escape_string($_POST['message']);

As is, it was looking for constants called department, name, email, message, etc. When it doesn't find such a constant, PHP (bizarrely) interprets it as a string ('department', etc). Obviously, this can easily break if you do defined such a constant later (though it's bad style to have lower-case constants).

Answer 6

Looks like the predefined fetch constants went away with the MySQL extension, so we need to add them before the first function...

//predifined fetch constants

define('MYSQL_BOTH',MYSQLI_BOTH);
define('MYSQL_NUM',MYSQLI_NUM);
define('MYSQL_ASSOC',MYSQLI_ASSOC);

I tested and succeeded.