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Posted by Ivαn Sαnchez Ortega on 11/18/62 11:40
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Dawsons wrote:
> say for example i have a variable called $definition_london
>
> Say for exaple that has not set value...
If it has no value, that varable name does not exist. Bye-bye.
> Is it possible to echoe thew ACTUAL variable name into a document, rather
> than the variables information?
No, because a variable can have more than one, due to the way PHP handles
references. Suppose the following code:
<?php
$a = 42;
$b =& $a;
$c =& $a;
unset ($a);
?>
At this point, what is the name of the variable that holds "42"?? $b, $c,
both, or nobody??
For this issue, do not think that a variable is a variable. Think that a
variable is an entry in an ordered map (with internal pointers),
implemented as a hash table that can map two (or more) keys to the same
value.
Let me (try to) explain this concept in pseudo-C:
function foo()
{
int* a;
int* b;
inc* c;
a = b = c = malloc(sizeof(int));
*a = 42;
a = NULL;
}
This would have a similar behaviour than the PHP code I posted up there. In
PHP, variable names "point" to the value. A reference is a pointer to that
value. Storing a reference is making two entries on the variable hash
tables point to the same value. When no references to a value are found,
that memory is freed.
Variable management in PHP is quite complicated internally, with all that
duplicate-on-write stuff when making copies of complex variables. The kind
of stuff that operating systems do when you fork() a process.
I agree with Ewoud: you can transverse the $GLOBALS superglobal array to
search for your value, but if you have any references over there, you may
find lots of problems. Lots.
- --
- ----------------------------------
IvΓ‘n SΓ‘nchez Ortega -i-punto-sanchez--arroba-mirame-punto-net
http://acm.asoc.fi.upm.es/~mr/
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