2

I have the following code:

$id = $_GET['id'];

echo '<br>' . 'id: ' . $id . '<br><br>';

echo '<pre>';
            print_r($itemQtys);
echo '</pre>';

echo '<br>' . 'itemqtys[id]: ' . $itemQtys[$id] . '<br>';

echo '<br>' . 'id: ' . $id . '<br>';

The output is:

id: 5

Array
(
[5] => 12
)

itemqtys[id]:

id: 5

As you can see, when I try to access the value in the array using the $id variable as the key, no value is returned. However, when I do this:

echo '<br>' . 'itemqtys[5]: ' . $itemQtys[5] . '<br>';

The result is:

itemqtys[5]: 12

Why can't I use a variable to specify the index in the array?

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3
  • 1
    where is $id? It's not set to anything in your example. How are you creating it? Commented May 20, 2012 at 22:05
  • I didn't think how it was being gotten was relevant, as I showed it's value. I've updated my question, however, and to answer your question: it is passed as a GET value. Commented May 20, 2012 at 22:07
  • 2
    ini_set('display_errors', 1); at the start of your script (or read the error log) and you'll probably see a warning which will indicate that $id isn't exactly what you expect. Commented May 20, 2012 at 22:10

2 Answers 2

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6

when debugging use var_dump() to inspect values. Notice var dump tells you the string length. right click > view html source when debugging too.

My guess is that $id is a string and has trailing whitespace characters.

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3 Comments

"My guess is that $id is a string and has trailing whitespace characters" sounds quite answery (and quite likely the error) to me.
I think my answer is pretty good actually- I both teach how to fish, and give a fish.
"I think my answer is pretty good actually- I both teach how to fish, and give a fish." LOL! Yes, you're answer was very good. Thank you! I checked if the id was a number via the function is_numeric(), but apparently in PHP something can still be a number even if it has a space in front of it! Thanks!
1

$id probably does not contain what you expect, cast it to an integer first.

Change your first line to:

$id = (int) $_GET['id'];

$_GET['id'] returns a string and you have to cast it to int before using it as an array index.

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5 Comments

php casts string to int (and vice versa) for array keys automatically. "and you have to cast it to int before passing it to you array." -- nope, they don't have to: ideone.com/7jdC5
@zerkms, I don't think you're entirely right. If you access an array like $itemQtys['5'] it will get casted correctly. But if there's a space (and that is entirely possible in user input), it won't cast the value but rather treat it as string: $itemQtys[' 5']. So trimming or better yet casting the user input isn't a bad idea. -- ideone.com/vx2St
@zerkms You are correct, but it seems bad practice to me to use a string when you know you need an integer.
@Czechnology: right, BUT answerer didn't state this explicitly, and said that it is required to cast to integer, without explanation for what reason. Without such examples the answer itself looks incorrect. "So trimming or better yet casting the user input isn't a bad idea" --- it is a good idea, but it is not a requirement.
ilanco - thank you for the suggestion on typecasting the GET value. I think I am going to start doing this from now on to stop this problem from occurring again. Thanks.

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