custom function for mysqli queries - php

Question

I'm trying my hand at custom functions in PHP in order to streamline a lot of stuff I'm otherwise doing manually. I'm damn new to custom functions so I'm not sure the limitations. Right now I'm trying to get data with MySQLi using custom functions Here's the code, and then I'll explain the issue:
function connect_db($db = 'db_username') {
iconv_set_encoding("internal_encoding", "UTF-8");
mb_language('uni');
mb_internal_encoding('UTF-8');
# $mysqli = new mysqli('host',$db,'password',$db);
if(mysqli_connect_errno())
{
die('connection error');
}
}
This one seems to be working fine. It's the next function I'm having more trouble with.
edit: Updated thanks to Jeremy1026's response
function do_query($db = 'default_db', $query) {
connect_db();
$result = $mysqli->query($query);
if(!$result){
trigger_error("data selection error");
}
while($row = $result->fetch_assoc()){
$result_array[] = $row;
}
return $result_array;
}
My host forces database names and usernames as the same, so if the db name is 'bob' the username to access it will be 'bob' as well, so that's why $db shows up twice in the connection.
The problem I'm having is that these two functions are in functions.php and being called from another page. I want to be able to pull the results from the query in that other page based on the column name. But I also need to be able to do this with formatting, so then maybe the while() loop has to happen on that page and not in a function? I want this to be as universal as possible, regardless of the page or the data, so that I can use these two functions for all connections and all queries of the three databases I'm running for the site.
God I hope I'm being clear.
Big thanks in advance for any suggestions. I've googled this a bit but it's tough to find anything that's not using obsolescent mysql_ prefixes or anything that's actually returning the data in a way that I can use.
Update: I'm now getting the following error when accessing the page in question:
Fatal error: Call to a member function query() on a non-object in /functions.php`
with the line in question being $result = $mysqli->query($query);. I assume that's because it thinks $query is undefined, but shouldn't it be getting the definition from being called in the page? This is that page's code:
$query = "SELECT * FROM `table`";
$myArray = do_query($db, $query);
echo $myArray['column_name'];

Answer 1

In your 2nd function you aren't returning any data, so it is getting lost. You need to tell it what to return, see below:
function do_query($db = 'default_db', $query) {
connect_db();
$result = $mysqli->query($query);
if(!$result){
trigger_error("data selection error");
}
while($row = $result->fetch_assoc()){
$result_array[] = $row;
}
return $result_array;
}
Then, when using the function you'll do something like:
$myArray = do_query($db, 'select column from table');
$myArray would then be populated with the results of your query.

Answer 2

This is a half-answer. The following single function works in place of the two.
function query_db($database, $new_query) {
$sqli = new mysqli('host', $database, 'password', $database);
$sqli->set_charset("utf8");
global $result;
if($result = $sqli->query($new_query)){
return $result;
}
}
By adding global $result I was able to access the results from the query, run from another page as
query_db("username","SELECT * FROM `column`");
while($row = $result->fetch_assoc()){
print_r($row);
}
It's more streamlined than I have without functions, but it's still not idea. If I have the connection to the database in another function, it doesn't work. If I try to put the while loop in the combined function, it doesn't work. Better than nothing, I guess.