When to use $$

jacqui1811

I know that to pass in a parameter byRef into a function you would use &$, but can anyone tell me when I would use $$ please.

volleytotal_ch

see this code as an example:

$var1 = "test";
$var2 = "var1";
echo $$var2;

Output of this code would be "test"!
just to explain:
$$var2 -> ${$var2} -> ${"var1"} -> $var1 -> "test"

Hope that helps

HalfaBee

The use of $$var is if you want to refence a varialble from a string.

Say you had a form with variables named v1 v2 v3

You could have a loop to show their contents.

for( $i=1;$i<3;$i++ )
{
$variable = "v".$i;
echo $$variable;
}
This would echo $v1 v2 v3.

Hope this helps.
HalfaBee

jacqui1811

Thanks you guys between both of your replies I think I can now understand.

jonnott

Has this syntax ($$) been removed from PHP now?

I've upgraded to 4.3.2 and wherever I've used this syntax it doesn't seem to work anymore.

Is there a config directive for it?

Instead I'm having to use $_REQUEST[$var_name]

Jon

HalfaBee

It is probably because the register_globals directive is turned off.

HalfaBee

Trs2988

For trivial reasons only... does $$$ work? Or is it just two? For example...

$var1 = "hi";
$var2 = "var1";
$var3 = "var2";

echo $$$var3;

Print "hi", or make an error?

HalfaBee

Try it and see 🙂
You may need to make it ${$$var3} ( not sure, give it a go. )

HalfaBee

Trs2988

Heh. Not only does that work, but look what else does:

$var1 = "hi";
$var2 = "var1";
$var3 = "var2";
$var4 = "var3";
$var5 = "var4";
$var6 = "var5";
$var7 = "var6";
$var8 = "var7";
$var9 = "var8";
$var10 = "var9";

echo $$$$$$$$$$var10;

Nice. 😃

HalfaBee

I can see a pyramid of uses for that 😃

HalfaBee

Trs2988

Oh, I'll find one. Trust me... 😉