Addressing an Object with Variable Variables

ayj

I'm sorry if this has been asked many times before, I have searched extensively but to no avail. Also, I admit objects are at the limits of my current understanding so I may get my terminology wrong, I hope nevertheless I can communicate the problem.

$posts[0]->post_title

has value 'my title' and prints out that value fine.

I have a string ex a POST variable

$thisstring = 'posts[0]->post_title'

I want to print out 'my title' again starting with $thisstring.

In reality the string can be anything, I do not know in advance it is an object or which value it is going to address. So this looks like variable variables to me, and for everything else, even multidimensional arrays, I am getting the right results.

With this though I either get parse errors or empty values. I have tried the basic

$thisvalue = $$thisstring

plus every combination of curly brackets, plus every combination of curly brackets plus text....that I can think of. I can't crack it.
There was an example in the notes to the php manual of

$b=${'a'.$i};

which seemed to me to indicate you could treat the contents of the curly brackets like a normal string eg

${'posts[0]'.'->'.'post_title'};

where I could replace those strings with variables, but no such luck.

Any ideas, suggestions?

Andrew

laserlight

Could you describe the problem that you intend to solve by solving this?

ayj

I'll try. It is a hacking / debugging tool I am building for myself.

It sits in the main loop of a large script that I am modifying (not mine) and I can ask the script for the values of any variables that are part of the script, ask for database info etc.

One of the common scenarios is that I want to know the contents of the object $posts (or any other object for that matter).

I type in 'posts' in the text field, hit Submit, and it goes off and does a print_r($posts) for me, and I can see, under the conditions of the script at that moment what $posts contains.

Sometimes I might not want to get the many different variables contained within posts. I might only want to know the first 'instance' (?) of the $posts field 'post title'. So I want to be able to type in

posts[0]->post_title

and I want it to tell me what that value actually is under the conditions of the script at that moment. Right now my debugging tool deals fine with simple variables, simple arrays, multi-d arrays and database queries BUT I can't get it to work with specific values in an object.

The script works via a form so the incoming request is via POST string variable. The action is inside a function however I have tested the issue outside the function etc and it appears to be nothing to do with the function or scope type issues.

Andrew

crimaniak

$thisstring = 'posts[0]->post_title';
$thisvalue = $$thisstring;

'posts[0]->post_title' is not entry in symbol table so you can't use operator $.
Use function eval() here.

ayj

Yes I thought of eval but I am reluctant to use it. While this will mainly be for my own use it may be that others use it too and eval is a rather powerful function to use on POST data if the user does not really watch themselves.

I don't fully understand your comment on the symbol table (need to go off and read more) but I find it surprising that I can make the other variable types work fine when they come in as strings but just not this one, which nevertheless returns a value when it is not in a string form.

Anyway, thanks for the response and help.

:-)

Andrew

crimaniak

Originally posted by ayj
Yes I thought of eval but I am reluctant to use it. While this will mainly be for my own use it may be that others use it too and eval is a rather powerful function to use on POST data if the user does not really watch themselves.

Make validator to be sure this is variable name. I think it's possible using preg_match and recursive patterns.