[Phpwm] updating an array

[alan dunn]

Thank you all for your replies - I haven't got the fix to work yet, but 
at least I know where to start looking.
alan dunn

David Goodwin wrote:
> alan dunn wrote :
>   
>> I am simply(!) trying to read through an array comparing the key with a 
>> string (product code) and where I find a match add the corresponding 
>> quantity to the existing quantity.
>>
>> if($match) {$prodarray[$key1] = $prodarray[$key1] + $qty2; }
>>
>> If I echo $prodarray[$key1] immediately after this line I get the 
>> increased value. But after continuing to cycle through the array the 
>> changed value is lost.
>>
>> I have some recollection of a group discussion about arrays being read 
>> into memory, or proxy values or some such? Can anyone shed light on how 
>> I get that value into the array?
>>     
>
> Right, to elabourate on my previous post; I suspect you're doing your
> matching/searching within a function.
>
> I can do the following :
>
> $list = array(5,4,3,2,1);
> foreach($list as $key => $value) {
>     if($value > 3) {
>         $list[$key] = 9;
>     }
> }
>
> print_r($list);
>
> which will show : 9,9,3,2,1
>
>
> If I change it to :
>
> <?php
> $list = array(5,4,3,2,1);
> function whatever($list) {
>     foreach($list as $key => $value) {
>         if($value > 3) {
>             $list[$key] = 9;
>         }
>     }
> }
> whatever($list);
> print_r($list);
>
> I'll get : 5,4,3,2,1
>
> This is because of the fact that PHP4 (and PHP5 when not using objects)
> does Pass by Value, not Pass by Reference.
> (Java always does Pass by Reference).
>
> i.e. When it runs inside the function it is a copy of the original
> variable passed in; so the whatever function's $list is a copy of the
> global $list. 
>
> If we want to fix this, we can either :
>
> a) Return $list from the function and assign it to $list globally
> (globally = outside a function scope)
> or
> b) Pass by reference
>
>
> To pass by reference you should put an '&' sign infront of variables in
> the function declaration i.e.
> $list = array(5,4,3,2,1);
> function whatever(&$list) {
>     foreach($list as $key => $value) {
>         if($value > 3) {
>             $list[$key] = 9;
>         }
>     }
> }
> whatever($list);
> print_r($list);
>
> will give 9,9,3,2,1
>
> Or
>
> $list = array(5,4,3,2,1);
> function whatever(&$list) {
>     foreach($list as $key => $value) {
>         if($value > 3) {
>             $list[$key] = 9;
>         }
>     }
>     return $list;
> }
> $list = whatever($list);
> print_r($list);
>
> which will also give 9,9,3,2,1
>
>
> >From a maintenance point of view, if you're going to use pass by
> reference, make sure you use the '&' signs in the function signature,
> and not at runtime when callign the function
>
> i.e.
> Good: function whatever(&$list) { ...... }
> Bad : $list = whatever(&$list);
>
> The reasoning being that you (the programmer) have to remember to put
> the '&' in in the latter case, but not in the former, which could lead
> to hard to track down bugs.
>
>
> I'll assume that helps, and answers your question/problem, even if the
> context isn't quite right.
>
> David
> </good-deed-of-the-day :-) >
>