Basic array question

webpoet

I´ve managed to build some pretty advanced stuff during my PHP-coding days, but I´ve always been a cut and paste programmer with no actually insight in how stuff works. Trying to change that now but got stuck at this:

$sql = "select name, lenght from ships;
$result = mysql_query($sql, $db_conn);
while($ships=mysql_fetch_array($result)) {

}

WHAT makes this loop work ? I mean how is PHP told that for each iteration of the while loop it should take the next row from the database result ?

Also, say I do this:

$sql = "select name, lenght from ships;
$result = mysql_query($sql, $db_conn);
$ships=mysql_fetch_array($result);

and want to echo for instance $ships[name] from the second line of the selected table, not the first, how would I go about doing that ? I do understand there are easier ways to do just that w/o using fetch_array but this question is more just to help me understand.

Thanx in advance for all replies.

trexx

WHAT makes this loop work ?

PHP has an internal result pointer. for each iteration it gets incremented by one. if there are no more results the expression in while gets false and it quits.

and want to echo for instance $ships[name] from the second line of the selected table, not the first

To move the mysql result pointer to the desired location use msql_data_seek( $pos ).

webpoet

Thanx.
I do have a followup on the second question tho. What if I wanted to creat a simillar array myself, not from mysql and loop thru it ?

Say I have this simple list of towns and integers representing them which I would like to be able to loop out at another point.

Stockholm 1
Moscow 4
Berlin 8
New York 5

etc.

Now I would like to use that simillar type of array that mysql fetch array returns, in other words $town[name] and $town[id] would be stockholm and 1 the first time the loop runs, then the next time moscow 4, etc etc.

How would I go about doing that ?

trexx

hm... i would fill them into a "normal" array

something like this:

$rs = mysql_query( 'select id, town_name from towns order by town_name' );
$towns = Array();
while( $row = mysql_fetch_assoc($rs) )
{
	$towns[$row['id']] = $row['town_name'];
}

your array would then looks like:

[8] => Berlin
[4] => Moscow
[5] => New York
[1] => Stockholm

webpoet

Ahh yes, but isn´t there any way to get two values into the same "row" of the array or something ? I mean say for instance I want do have a dropdownlist for the towns, with their name as options and number as value.
I could ofcorse do that in html but what if I wanted to predefine them and instead loop em out as options ?

trexx

that's exactly what you've got here =)

the numeric index of the array is your ID (=option-value) and the value is the option-text. with that you can easily create a dropdown. i posted a function to do that yesterday... err... it's here:

http://www.phpbuilder.com/board/showthread.php?s=&threadid=10231977

webpoet

But I can´t predefine the keys to with that one right ?

trexx

sure... in case you load them from your database the IDs and names are already predefined.
in case you wanna define them manually you only have to do something like this:

$myTowns = Array( 1 => 'Moscow', 4 => 'Zurich', 5 => 'Bern' );

and put that array as an argument into the htmlSelect() function.

webpoet

Thanx!

Another question: How does the $result look ? I mean how does PHP know what should go into each instance of the array ?

/Pesky n00b 😛

trexx

you should really take a look at this one here 😃
http://www.php.net/manual/en/language.types.array.php

a result set is nothing else than a normal associative array in php. if you fetch your RS with fetch_assoc you'll get the colum-names from your DB table as indizes and with fetch_row numeric indizes. with fetch_array you have both, numeric AND string indizes =)

webpoet

I had hoped not to do this but oh well... goes and RTFM.

Thanx for answering my questions man, wont bug you more 😛