Can't view a message through php? - php

Question

Okay, I have a php code for my mail.php, so that if the current user id doesn't match the to or from id, it will show an error message, but I tested it out and any use can view the message, here's the code :
if (!$mail['to_id'] == $account['id'] && !$mail['from_id'] == $account['id']) {
$system->message(L_ERROR, L_MAIL_ERROR_PERMISSION, './?area=forum&s=mail', L_CONTINUE);
}
But when I added != instead of ==, it shows an error message for everyone, including the people who sent the message. Does anyone know how I can fix this problems?

Answer 1

Use this code instead.
if ($mail['to_id'] != $account['id'] && $mail['from_id'] != $account['id']) {
$system->message(L_ERROR, L_MAIL_ERROR_PERMISSION, './?area=forum&s=mail', L_CONTINUE);
}

Answer 2

Your logic is:
!$mail['to_id'] == $account['id']
&&
!$mail['from_id'] == $account['id']
The problem stems from doing this:
!$mail['to_id']
and
!$mail['from_id']
The inverse operator (!) flips the value of what it's being applied to. In this case, you're flipping the value of $mail ID's. That's probably not going to do what you're thinking since those ID's, I'm assuming, are integers.
It might help to think of this in the positive and then reverse the whole thing.
The positive is:
$mail['to_id'] == $account['id']
&&
$mail['from_id'] == $account['id']
The inverse of it is wrapping the whole thing in a "!" (note the parenthesis):
!(
$mail['to_id'] == $account['id']
&&
$mail['from_id'] == $account['id']
)
We can use the rules of Algebra to convert that statement by multiplying "!" against each element (including the AND operator).
!($mail['to_id'] == $account['id']) // Note you apply the inverse of to the whole expression
!&& // this isn't an actual code but for demonstration purposes
!($mail['from_id'] == $account['id']) // Note you apply the inverse of to the whole expression
Which simplifies into:
$mail['to_id'] != $account['id'] // Not Equal is inverse of equal
|| // the inverse of && (AND) is || (OR)
$mail['from_id'] != $account['id'] // Not Equal is inverse of equal
Which states:
"If the Mail_To OR Mail_From ID doesn't match the Account ID, execute the following code"
So, at the end of the day you should be able to use:
if( $mail['to_id'] != $account['id'] || $mail['from_id'] != $account['id'] )
{
// do something
}
or
if( !( $mail['to_id'] == $account['id'] && $mail['from_id'] == $account['id']) )
{
// do something
}
Both say the same thing.
I hope that helps!