After looking up the === operator, I see exactly what you mean. Thanks for
your help everyone. I think the confusion was that I was always under the
impression that assignment is either true or false; I would never have
guessed it was equal to the value assigned. Your examples really helped to
solidify the concept though!
PS: I have to say that PHP has the *best* documentation I've ever seen
beside Java.
Thanks again!
On Wed, Mar 31, 2010 at 4:43 AM, Richard Quadling
<rquadling@xxxxxxxxxxxxxx>wrote:
> On 31 March 2010 05:45, Matty Sarro <msarro@xxxxxxxxx> wrote:
> > That explains it perfectly, thanks you!
> >
> > On Wed, Mar 31, 2010 at 12:40 AM, Tommy Pham <tommyhp2@xxxxxxxxx> wrote:
> >
> >> On Tue, Mar 30, 2010 at 9:22 PM, Matty Sarro <msarro@xxxxxxxxx> wrote:
> >> > Hey all!
> >> > This is probably my second post on the list, so please be gentle.
> Right
> >> now
> >> > I am running through the "Heads First PHP and MySQL" book from
> O'Reilly.
> >> > It's been quite enjoyable so far, but I have some questions about some
> of
> >> > the code they're using in one of the chapters.
> >> >
> >> > Basically the code is retreiving rows from a DB, and I'm just not
> getting
> >> > the explanation of how it works.
> >> >
> >> > Here's the code:
> >> >
> >> > $result=mysqli_query($dbc,$query)
> >> >
> >> > while($row=mysqli_fetch_array($result)){
> >> > echo $row['first_name'].' '.$row['last_name'].' : '. $row['email'] .
> '<br
> >> > />';
> >> > }
> >> >
> >> > Now, I know what it does, but I don't understand how the conditional
> >> > statement in the while loop works. Isn't an assignment operation
> always
> >> > going to result in a "true" condition? Even if
> >> mysqli_fetch_array($result)
> >> > returned empty values (or null) wouldn't the actual assignment to $row
> >> still
> >> > be considered a true statement? I would have sworn that assignment
> >> > operations ALWAYS equated to true if used in conditional operations.
> >> > Please help explain! :)
> >> >
> >> > Thanks so much!
> >> > -Matty
> >> >
> >>
> >> http://www.php.net/manual/en/function.mysql-fetch-array.php
> >>
> >> "Returns an array of strings that corresponds to the fetched row, or
> >> FALSE if there are no more rows."
> >>
> >> while($row=mysqli_fetch_array($result)) is equivalent to this:
> >>
> >> $row=mysqli_fetch_array($result);
> >> while ($row){
> >>
> >> // do something
> >>
> >> $row=mysqli_fetch_array($result);
> >> }
> >>
> >> So, if $row is not equal to FALSE, the loop will happens.
> >>
> >
>
> Another part to the answer is the value of the assignment. From the
> documentation (
> http://docs.php.net/manual/en/language.operators.assignment.php),
> ...
>
> "The value of an assignment expression is the value assigned."
>
> while($row = mysqli_fetch_array($result))
>
>
> But there is a significant issue here. Whilst not attributable to the
> mysqli_fetch_array() function, it is certainly possible to give
> yourself a significant WTF moment with it.
>
>
> May be will be easier to see the problem when the code is written as ...
>
> while(False === ($row = mysqli_fetch_array($result)))
>
> No?
>
>
> If I say ...
>
> 0 == False
>
> does that help?
>
>
>
> Without running the 2 stupid scripts below, what output should you get?
>
> <?php while($pos = strpos('abc', 'a')) { echo 'a';} ?>
>
> and
>
> <?php while($pos = strpos('abc', 'z')) { echo 'z';} ?>
>
> Clearly, they should be different, yes?
>
> Unfortunately, they won't be.
>
> The first call returns 0 and the second returns False.
>
> And as 0 == False, the while() does not loop.
>
> But ...
>
> <?php while(False !== ($pos = strpos('abc', 'a'))) { echo 'a';} ?>
>
> and
>
> <?php while(False !== ($pos = strpos('abc', 'z'))) { echo 'z';} ?>
>
> now operate correctly. The first one runs forever, printing a's and
> the second one quits straight away.
>
> By always using ...
>
> while(False !== ($var = function($param)))
>
> you can clearly differentiate between functions that return false to
> indicate failure and 0 to indicate a position or actual value.
>
> Regards,
>
> Richard.
>
>
>
>
>
> --
> -----
> Richard Quadling
> "Standing on the shoulders of some very clever giants!"
> EE : http://www.experts-exchange.com/M_248814.html
> EE4Free : http://www.experts-exchange.com/becomeAnExpert.jsp
> Zend Certified Engineer : http://zend.com/zce.php?c=ZEND002498&r=213474731
> ZOPA : http://uk.zopa.com/member/RQuadling
>
