Making global var from inside a function in PHP - php

Question

I am trying to define dynamically variables. I am using a function for this, but I don't know how to define the new var as global (because it never created before the function).
is that possible ?
Thanks.
edit
ok, this is what I've built. is it that dangerous ?
function extract_values($row) {
foreach ($row as $key => $value){
global $$key;
$$key = $value;
}
}
and then I'm trying to make my life easier like that:
$result = mysql_query("SELECT first_name, last_name, address FROM users ORDER BY id ASC");
while ($row = mysql_fetch_array($result)){
extract_values($row);
#[do some stuff with the variables.]#
}
I am doing it to save time. instead of creating for each column it's own variable like
$first_name = $row['first_name'];
This function does that for me.
I don't see why in this case it might be dangerous..
or as usuall, i am missing something..

Answer 1

Try this:
function doSomething() {
global $x;
$x = 5;
}
If you prefer to save a couple of bytes, you can use the $_GLOBALS array for this:
$_GLOBALS['x'] = 5;

Answer 2

Regarding your edit: It makes your code less understandable.
Actually, there already exists a function that is doing this: extract().
while (($row = mysql_fetch_assoc($result))){
extract($row);
// ...
}
extract() is even better, because it lets you specify what should happen if the variable already exists and/or lets you specify a prefix (so you don't overwrite already existing variables with that name). E.g. you could do:
extract($row, EXTR_PREFIX_ALL, 'db');
which would result in $db_first_name etc.
Surly, extract() is also doing some internal work here, but using built-in functions is always better than creating your own.
Another possibility would be to use list():
while (($row = mysql_fetch_row($result))){
list($first_name, $last_name, $address) = $row;
// ...
}

Answer 3

You can do it in two ways:
Make the variable global using the global keyword:
function fun1() {
global $foo;
$foo = 1;
}
Alternatively you can also create an new element in the $GLOBALS array:
function fun2() {
$GLOBALS['bar'] = 1;
}
Working code
Remember that these are considered bad practice, a function should have local variables invisible outside and should get inputs through the arguments passed. You should avoid getting arguments though global variables and must completely avoid crating global variables.