How to verify if $_GET exists?

Question

So, I have some PHP code that looks a bit like this:

<body>
    The ID is 

    <?php
    echo $_GET["id"] . "!";
    ?>

</body>

Now, when I pass an ID like http://localhost/myphp.php?id=26 it works alright, but if there is no ID like just http://localhost/myphp.php then it outputs:

The ID is
Notice: Undefined index: id in C:\xampp\htdocs\myphp.php on line 9
!

I have searched for a way to fix this but I cannot find any way to check if a URL variable exists. I know there must be a way though.

Undefined index is not an error, it is just a warning. You can turn off warning by editing the `.htaccess` file. — www139, Dec 28 '15 at 22:52
verifying if `$_GET` exists (like in the subject) is actually another question, you're trying to verify if `$_GET["id"]` exists... — eis, May 16 '16 at 09:53

score 160 · Accepted Answer · edited Nov 29 '20 at 11:13

You can use isset function:

if(isset($_GET['id'])) {
    // id index exists
}

You can create a handy function to return default value if index doesn't exist:

function Get($index, $defaultValue) {
    return isset($_GET[$index]) ? $_GET[$index] : $defaultValue;
}

// prints "invalid id" if $_GET['id'] is not set
echo Get('id', 'invalid id');

You can also try to validate it at the same time:

function GetInt($index, $defaultValue) {
    return isset($_GET[$index]) && ctype_digit($_GET[$index])
            ? (int)$_GET[$index] 
            : $defaultValue;
}

// prints 0 if $_GET['id'] is not set or is not numeric
echo GetInt('id', 0);

score 19 · Answer 2 · answered Aug 18 '12 at 15:15

19

   if (isset($_GET["id"])){
        //do stuff
    }

answered Aug 18 '12 at 15:15

Makita

1,812
12
15

Asaph · Answer 3 · 2012-08-18T15:24:38.783

9

You can use the array_key_exists() built-in function:

if (array_key_exists('id', $_GET)) {
    echo $_GET['id'];
}

or the isset() built-in function:

if (isset($_GET['id'])) {
    echo $_GET['id'];
}

edited Aug 18 '12 at 15:24

answered Aug 18 '12 at 15:17

Asaph

159,146
25
197
199

1

Is there any benefit to using one over the other? array_key_exists seems more right, but I've almost always used isset. – Rikki Dec 13 '14 at 00:18

score 9 · Answer 4 · answered Aug 18 '12 at 15:19

9

Normally it is quite good to do:

echo isset($_GET['id']) ? $_GET['id'] : 'wtf';

This is so when assigning the var to other variables you can do defaults all in one breath instead of constantly using if statements to just give them a default value if they are not set.

answered Aug 18 '12 at 15:19

Sammaye

43,242
7
104
146

4

WTF is an example...plus it is `wtf` not `wft` – Sammaye Aug 18 '12 at 15:27
1

Better options would be `null` or `0`. – Asaph Aug 18 '12 at 20:28
1

@Asaph `wtf` is the new `null` :P though he was also echoing and as the OP said themselves they replaced `wtf` with `No ID!` and that's really what it was designed for, ehcoing `null` isn't very useful, in this case `wtf` was more useful than `null` imo – Sammaye Aug 18 '12 at 20:52
@Asaph Also 0 could be a valid ID so that's not such a good response for it not being set either. – Sammaye Aug 18 '12 at 20:53
1

`wtf` is an awsome value. – Alkis Kalogeris Aug 25 '14 at 14:04

score 6 · Answer 5 · edited Mar 01 '21 at 16:38

6

You are use PHP isset

Example

if (isset($_GET["id"])) {
    echo $_GET["id"];
}

edited Mar 01 '21 at 16:38

Andrew Truckle

17,769
16
66
164

answered Aug 18 '12 at 15:16

Baba

94,024
28
166
217

yeah .. but do to the documentation for more examples – Baba Aug 18 '12 at 15:17

Julien · Answer 6 · 2012-08-18T15:38:03.850

5

Use and empty() whit negation (for test if not empty)

if(!empty($_GET['id'])) {
    // if get id is not empty
}

edited Aug 18 '12 at 15:38

answered Aug 18 '12 at 15:16

Julien

1,946
3
33
51

1

What if the id is 0? Remember empty returns false for numerous things. – Sammaye Aug 18 '12 at 16:18

illeas · Answer 7 · 2017-11-24T05:52:24.160

0

Please try it:

if(isset($_GET['id']) && !empty($_GET['id'])){
   echo $_GET["id"];
 }

edited Nov 24 '17 at 05:52

answered May 16 '16 at 09:31

illeas

300
3
18

2

`empty($_GET['id'])` is translated to `!isset($var) || $var == false.`, so the `isset($_GET['id'])` is not required. – lcjury Jan 23 '17 at 13:07

How to verify if $_GET exists?

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