create variables on the fly (dynamically)

[bilibytes]

hi,

i was wondering how to create variables on the fly,
by this i mean: i have a pair of strings or an associative array with one string for Key and another for Value:

$var1 = 'hello';
$var2 = 'johnny';

or --------------

array('hello'=>'johnny');

how could i manage to make of these two strings, a vairable with one becoming the name of the variable and the other the value.

echo $hello; //prints johnny

is there a thing like:

${$var1} = $var2;

?


Thankyou.

[bilibytes]

The answer is to use eval()

if you want a variable to have the name of another variable's value, do :

$my_var_name = 'some_text'
$my_value = 'some other text' 
 
eval( '$'.$my_var_name.' = \' '. $my_value.' \';' );
 

(of course, you cannot do a variable with a wrong syntax: $myvalue ='some text'. 'some text' could never become the name of a variable, even if you write it yourself. $some text = parse error...)

[Atli]

Yes, you can do that.

In fact, if you combine your first example with your last example and then echo the variable $hello, you should get "johnny".

You can also do this using array key=>value pairs by using a foreach loop, like:

<?php
$array = array('hello' => 'John');
 
foreach($array as $_key => $_value) {
    ${$_key} = $_value;
}
 
echo $hello;
?>
 

Which would print "John".

I have to ask tho, why are you doing this?
It seems like sort of a backwards logic, taking arrays and importing them into variables.

Why don't you just use the arrays as they are?
Why do you want to do $hello rather than $arr['hello']?

[Atli]

The answer is to use eval()

if you want a variable to have the name of another variable's value, do :

No. eval is never the answer! It's very very dangerous, if not just sloppy, to use eval. It causes all sorts of performance and security issues.

You can simply do:

<?php
$key = 'hello';
$value = 'johnny';
 
${$key} = $value;
?>
 

[bilibytes]

ok thanks for clarifying.

could i do:

$this->{key($array)} = $array[key($array)];

?

the point is that i want to make a class that would handle all the HTTP requests of my application.

and i am trying to put the $_REQUEST array's content into variables of an instance of that class, without having to put to many if conditions.

is it good to do this?

i think it clarifies the code but maybe its not a good practice.

please tell me if what i want to do is totally stupid. maybe its better to just use $_REQUEST['key']...


as i saw that, in PHP manual, in the extract() function documentation, they talk about using extract to handle $_REQUEST array, i thought it would be great to make an object for that. but there is no option to extract() the array content into object variables" $this->variable". extract() only extracts to normal vairables "$variable". that is why, i was trying to figure out how to do that...

long story!

thankyou

[Atli]

So basically, all you are trying to do is;

// to change this
echo $_REQUEST['name'];
 
// into this?
$request = new RequestObject();
echo $request->name;
 

Why?

Unless you plan on having your class automatically sanitize or validate your fields?

I usually get request variables via a controller class that automatically sanitizes the data, but it doesn't need to be as complicated as you are trying to make it.
A simple static "getField($key)" method that gets and processes the field before returning it to you usually does fine.