Including my connection.php in a function doesn't work php

Question

Working on a small project with some simple sql query injection in my php file. I have created a functions.php file with a function called function displayimage(). I include my function file in my index file and use the function like so

index.php

            <div class="col-lg-2">
              <?php displayimage(); ?>
            </div>

Functions.php

 function displayimage()
{

$dbCon = mysqli_connect("localhost", "root", "root", "testdb");

if (mysqli_connect_errno()) {
    echo "Failed to connect: " . mysqli_connect_error();
}

$sql= "SELECT * FROM `images` ORDER BY `images`.`id` DESC ";

$query=mysqli_query($dbCon, $sql);

if ($row = mysqli_fetch_array($query))
{
    echo '<img class="img-responsive" style="margin-top: 10px;" src="data:image;base64,'.$row[2].' "> ';
}

mysqli_close($dbCon);

 }
 ?>

So it works fine but.. I tried to clean my code by putting the database connection in a seperate file, and including it like include('connection.php');. Unfortunately my code doesn't work anymore, and the content won't show up at my index file. My PHPStorm says that $dbCon is a undefinable variable now. What am I doing wrong here?

new functions.php

function displayimage()
{

include('connection.php');

$sql= "SELECT * FROM `images` ORDER BY `images`.`id` DESC ";

$query=mysqli_query($dbCon, $sql);

if ($row = mysqli_fetch_array($query))
{
    echo '<img class="img-responsive" style="margin-top: 10px;" src="data:image;base64,'.$row[2].' "> ';
}

mysqli_close($dbCon);

 }
 ?>

connection.php

$dbCon = mysqli_connect("localhost", "root", "root", "testdb");

if (mysqli_connect_errno()) {
echo "Failed to connect: " . mysqli_connect_error();
}

`$dbCon` doesn't exist inside the function, functions have a local scope while `$dbCon` is (probably) created in the global scope. You need to pass the connection into the function `displayImage($dbCon)` and/or restructure your code. Please do not use globals. — JimL, Mar 13 '16 at 21:27
Functions doesn't "support" variables that are not included or scoped in them. You need to either make variable global which is bad idea, or recall it — Steven Dropper, Mar 13 '16 at 21:28
@StevenDropper Alright, So I have to keep my code like the way it was? So add my connection variable above my code in the function itself? — Giesburts, Mar 13 '16 at 21:31
@GlennGijsberts - Yes, your code with include will work. BTW: Never use global variables if you're not making anything small like a plugin or so... — Steven Dropper, Mar 13 '16 at 21:39

Xorifelse · Answer 1 · 2016-03-13T21:46:33.787

You should include connections.php on the top on your page if you want to make a connection to a database. However if you're using mysqli I would recommend using the object orientated syntax over the procedural. That way you don't have to parse the $connection variable each time you query.

require_once 'connection.php';

function displayimage(){
  global $dbCon;

  $sql= "SELECT * FROM `images` ORDER BY `images`.`id` DESC ";
  if($qry= mysqli_query($dbCon, $sql) != false){
    // query ran successfully, here you should actually continue the code..
    while($row = mysqli_fetch_array($query)){
      echo '<img class="img-responsive" style="margin-top: 10px;" src="data:image;base64,'.$row[2].' "> ';
    }
  } else {
    echo 'failed to retrieve images from the database.';
  } 


}

Also, you don't have to close the connection every time when you're done querying. Its done automatically at the end of the script and without it it can continue to use the already opened connection.

However it is bad practice to use global variables in functions, just make sure you never overwrite the $dbCon variable, it might happen when using code from somebody else.

Alright. I see, it works and maybe this way is a bit cleaner than it was before. But, Above, 2 people recommend not to use globals.. Why should I use it or not? — Giesburts, Mar 13 '16 at 21:40
I've made some edits, but to answer your question I'd say its there to be used however in this particular case we're talking about a fragile variable. If it gets overwritten, your code will fail big time and with the error handling you where using (which is none) you're unable to diagnose it. But it comes with experience to find ways to protect the variable. Wrapping in classes for example (which is why I would recommend using the mysqli OO-Style (or PDO)) — Xorifelse, Mar 13 '16 at 21:53

Including my connection.php in a function doesn't work php

1 Answers1