> -----Original Message-----
> From: Martin Peck [mailto:[EMAIL PROTECTED]
> Sent: 28 July 2003 15:33
>
> The following code illustrates a problem I've got with
> references (running
> on PHP 4.3.2). Can anyone explain it for me? Thanks in
> advance for any
> assistance!
> Martin
>
> <?php
>
> $globalvariable = 0;
> $one = 1;
>
> //want to set up $globalvariable as a reference to $one
> setglobal($one);
>
> echo $globalvariable; //prints 0, not 1
>
> function setglobal(&$one)
> {
> global $globalvariable;
PHP actually handles this by executing the equivalent of:
$globalvariable = &$GLOBALS['globalvariable'];
-- that is, it creates a $globalvariable *which is local to the function*
and makes it be a reference to the global-scope variable of the same name.
> $globalvariable =& $one;
This says to make the local $globalvariable be a reference to $one, *not* to
assign the value of $one to the variable referred to by $globalvariable --
so you've just overwritten the reference to the global $globalvariable with
a reference to $one! This means that you now have no way to refer to the
global-scope $globalvariable from within this function.
There are two key concepts here, which often seem to get overlooked:
(1) When you assign a reference to a variable which already contains a
reference, the action is to *replace* the existing reference with the new
one (*not* to assign the new reference through the existing reference).
(2) In a function, the global and static mechanisms are both handles by
defining variables local to the function which are *references* to the
appropriate location (thus, you *cannot* assign references to global or
static variables).
This is explained, albeit in a rather oblique way, on the manual page at
http://www.php.net/manual/en/language.variables.scope.php
Cheers!
Mike
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Mike Ford, Electronic Information Services Adviser,
Learning Support Services, Learning & Information Services,
JG125, James Graham Building, Leeds Metropolitan University,
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