how does while($row = mysql_fetch_array) work?

Stamatis · January 30th, 2012, 06:26 PM

Hello all,
I'm new in php and i have a question.

Assume we have the following code (from Wrox Beg php6 web development)

while ($row = mysql_fetch_array($result)) {

extract($row);

echo $movie_name . ' - ' . $movie_type . '<br />';
}

I would like to explain me how does while work? at first the $row gets the value of mysql_fetch_array($result) ? and after that? what value of $row does stop the loop? perhaps it is a dummie question but i can't understand it....

Thank you

UseLess · January 31st, 2012, 07:54 AM

Greetings,

The loop ends when $row is false, i.e. no array is returned from the db.

So if you had a table with 5 rows you would get 5 results back once the line;

Code:

while ($row = mysql_fetch_array($result))

tries to get row 6 you get nothing back and the loop ends.

Stamatis · January 31st, 2012, 08:23 AM

Hi useless and thanks for your reply...
However i cannot understand how the $row gets the value.The = in php is set of a variable or an equality? is there the == in the while or not? because for example in C if we have the same example we have an infitite loop. here is difference?

Perhaps i have not understand how the set of variables work in php loops

Sorry for this dummie questions but i try to understand

Thank you

UseLess · January 31st, 2012, 10:06 AM

Greetings,

= assigns variable on left the value on the right.
== determines equality
=== determines equality AND type

So you'd use = like so;

Code:

$somevar = 'A string variable';

you'd then use == like so;

Code:

if( $somevar == 'A string variable' )
{
echo 'Match found';
}
else
{
echo 'Match NOT found';
}

and finally;

Code:

if( ($pos = strpos($somevar, 'string')) !== false )
{
	echo 'Found "string" at position: ' . $pos . ' in string: "' . $somevar .'"';
}

Stamatis · January 31st, 2012, 11:30 AM

Hi

I can understand that you writed but i can't understand how the = work in the while.

while ($row = mysql_fetch_array($result))

Regarding the adove you writed in your post (
= assigns variable on left the value on the right.) the $row at first get the value of mysql_fetch_array($result).... so... when it gets the same value how the loop works and we don't have a infinite loop, when every time has the value of the "mysql_fetch_array($result)" For example it the same with while($row = 5)... so there is an infinite loop here.

Thanks and sorry again

UseLess · January 31st, 2012, 04:12 PM

Greetings,

Like I said in my previous post as long as $row is not false then the loop will continue to loop, once $row is false (like when nothing is returned from the db) then the loop ends.

Or put another way as long as the expression, in this case $row = mysql_fetch_array($result), is true then the while loop will continue to loop. The loop ends when the expression evaluates to false.

More info here: http://www.php.net/manual/en/control...ures.while.php

Stamatis · January 31st, 2012, 05:51 PM

ok I understand now!

Thanks a lot!

Best regards