Using variables inside php function - php

Question

trying to make my website a bit tidier and simpler to maintain so am trying to move alot of repeated code into functions.
I have a function that takes an argument for an ID, runs a database check using this ID in the where claus and then sets a new variable for the rowCount returned.
However it keeps returning 0 / nothing.
I have made a simple example of what im doing:
$buildID = 5;
function select_All_Comments_From_ID($buildID){
$idNew = $buildID;
global $idNew
}
select_All_Comments_From_ID($buildID);
echo $idNew;
Any idea why this is happening?
Here is what it actually looks like:
function select_All_Comments_From_ID($buildID){
$query = " SELECT * FROM comments WHERE buildID = :buildID";
$query_params = array(':buildID' => $buildID);
try {
$stmt = $db->prepare($query);
$result = $stmt->execute($query_params);
$row = $stmt->fetch();
$countComments = $stmt->rowCount();
global $countComments;
}
catch(PDOException $ex) { die();
}
}
I then am trying to use
$countComments
But no luck.
The code itself works when not in the function.

Answer 1

global $idNew affects the variable lookup just when it's executed - not before. E.g. take a look at
<?php
$a = 9;
foo();
function foo() {
$a = 5; // this sets the value for the variable in the local lookup table
echo $a, "\r\n"; // scope of $a is still local -> 5
global $a; // now the lookup for "a" is switched to the global scope
echo $a, "\r\n"; // $a "points" to the global value -> 9
}
the output is
5
9
and in your case
function select_All_Comments_From_ID($buildID){
$idNew = $buildID;
global $idNew
}
the function writes the value to its local $idNew and then the lookup for idNew is switched to the global scope - but that doesn't copy the local value to the global scope; just the lookup has been changed.
Anyway as pointed out before you really should return the values instead of setting them globally. And if all you're interested in is the number of (matching) records in a table - not the payload data of the records - use a SELECT Count(...) query. Otherwise your script transfers all the data from the database server into the memory space of your php instance ...for nothing but heating up the cpu and memory.
function select_All_Comments_From_ID($buildID){
$query = " SELECT Count(*) as c FROM comments WHERE buildID = :buildID";
$query_params = array(':buildID' => $buildID);
try {
// what's $db here ?
// neither has it been passed to the function nor is it fetched from the global scope
$stmt = $db->prepare($query);
$result = $stmt->execute($query_params);
$row = $stmt->fetch();
return $row['c'];
}
catch(PDOException $ex) {
// using die(...) is crude, even more so without any notice/text
die();
}
}

Answer 2

You have to define $countComments at outside of the function even if it defined as a global at inside of function.
Example :
<?php
$a = 1;
$b = 2;
function Sum()
{
global $a, $b;
$b = $a + $b;
}
Sum();
echo $b;
?>

Answer 3

You can return a value from your function, instead of using a Global, like this:
function select_All_Comments_From_ID($buildID){
$query = " SELECT * FROM comments WHERE buildID = :buildID";
$query_params = array(':buildID' => $buildID);
try {
$stmt = $db->prepare($query);
$stmt->execute($query_params);
$row = $stmt->fetch();
$countComments = $stmt->rowCount();
return $countComments; //sends the value back outside the scope of the function
}
catch(PDOException $ex) { die(); }
}
When you call the function, you need a variable to catch the return value, like this:
$buildID = 5;
$countComments = select_All_Comments_From_ID($buildID);
echo $countComments;

Answer 4

change
$countComments = $stmt->rowCount();
global $countComments;
in
$GLOBALS['countComments'] = $stmt->rowCount();
By the way, the comment is right, that's an awful solution, you should really change it.