PHP Variable assignment does not work as expected

Question

I am trying to assign parameters listed in the URL save into my variables. You can see the procedure here:

<?php

$browser;
$version;
$page;

foreach($_GET as $key => $value) {
  if (strcmp($key, "browser")) {
    $browser = $value;
  }
  elseif (strcmp($key, "version")) {
    $version = $value;
  }
  elseif (strcmp($key, "page")) {
    $page = $value;
  }
}

echo $browser;
echo $version;
echo $page;
?>

But unfortunately, it only prints out the browser and the version. The page does not appear. Yes, the page parameter is definitely written correctly in the URL. If I change code like this, the variables get printed out correctly:

 <?php
    
    foreach($_GET as $key => $value) {
      if (strcmp($key, "browser")) {
        echo $value;
      }
      elseif (strcmp($key, "version")) {
        echo $value;
      }
      elseif (strcmp($key, "page")) {
        echo $value;
      }
    }
    ?>

Link shematik: ./bglink/addstats.php?browser=Chrome&version=96&page=index
Thanks in advance. Filip.

In that case, assume a small corruption in the file you have your code in. Delete the whole foreach loop and rewrite it. It sound unlikely, but it would not be the first time this has happened to me. — RiggsFolly
– RiggsFolly, Commented Dec 15, 2021 at 15:19

iainn · Accepted Answer · 2021-12-15 15:48:02Z

1

strcmp doesn't do what you think it does.

It can return -1, 0 or 1 depending on the comparison of the two string, not true or false. Your loop isn't finding the strings that are equal, it actually will print the first case where $key does not equal the string you're asking about, since both -1 and 1 will evaluate to true.

Running your original code with some extra debug output shows that you're actually overwriting the variables with other elements from the loop:

Browser: my page
Version: my browser
Page:

See https://3v4l.org/QFSAl

answered Dec 15, 2021 at 15:48

iainn

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Comments

Olivier D · Accepted Answer · 2021-12-15 15:16:47Z

1

Why not write something like that ?

$browser = $_GET['browser'];
$version = $_GET['version'];
$page = $_GET['page'];

answered Dec 15, 2021 at 15:16

Olivier D

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3 Comments

Filip Degenhart Over a year ago

Yeah, I am going to use that in production. Already inserted it. I just came up with this code and wondered so hard what is wrong with this snippet. I am so interested at code I do not need that I try to find out the solution.

chaos505 Over a year ago

accessing $_GET directly offers a security risk

Filip Degenhart Over a year ago

@chaos505 Ah ok. Thanks

chaos505 · Accepted Answer · 2021-12-15 15:47:01Z

0

The secure way of reading $_GET would be to use filter_input()

$browser = filter_input(INPUT_GET, 'browser');
$version = filter_input(INPUT_GET, 'version');
$page = filter_input(INPUT_GET, 'page');

https://www.php.net/manual/en/function.filter-input.php

But with regurads to original question, the issue is with (strcmp($key, "browser")) should be (strcmp($key, "browser") == 0) where 0 indicates a match. But if no condition is specified for if() then 0 will read FALSE

edited Dec 15, 2021 at 15:47

answered Dec 15, 2021 at 15:35

chaos505

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