Stupid question Re: Vars

[PaganJim]

It is my understanding that vars do not have to be declared before use in PHP.

I have a little test script that starts:

    <?php
      $testing; // declare without assigning
      echo "is null? ".is_null($testing); // checks if null
      echo "<br/>

Pretty straightforward, or so it seems. The output I get from this is:
Warning: Undefined variable $testing in index.php on line 3
is null? 1

So it executes, but why the error when I first check the variable? It would seem that if I don’t really need to declare then I should not get any error?

One more thing I noticed… I changed the line to read $testing = ‘’; // declare without assigning so now I do not get an error, but I also do not get any output from the is_null so what I get is is null? with nothing behind it…

Can anyone provide any insight into this?

Thanks for reading!
Jim

[phdr]

A variable by itself, i.e. the $testing; line, does nothing. This is not a declaration nor a reference to the variable. It doesn’t even produce any php bytecode (just confirmed), which is why it doesn’t produce an undefined error for that line.

@PaganJim

I changed the line to read $testing = ‘’; // declare without assigning

That’s assigning an empty string to the variable.

@PaganJim

I also do not get any output from the is_null

The result is a false value, which when echoed doesn’t display anything (a true value when echoed results in a 1 being displayed.) You can use var_dump() to see the true/false value from the is_null() call.

[jpajak]

Hi PaganJim,

you don’t need to declare variables in PHP - it does not have variable declaration syntax. You can only initialize a variable by assigning a value to a new variable.

is_null strictly checks whether the variable value is null, it does not check whether the variable has been initialized.

If you want to check whether a variable has been initialized, you can use isset or empty, like this:

empty($testing);
isset($testing);

Both of which will evaluate to a boolean. Just be careful when you concatenate a boolean with a string in PHP, since a boolean of value false concatenates to an empty string.

[PaganJim]

Thank you very much for reading and the replies. Both are very helpful and greatly appreciated.

But, it throwing and error like Warning: Undefined variable $testing in index.php on line 9 kinda threw me for a loop I guess. I had read that there was not need to declare vars. I guess I just didn’t expect it to be a no-no. I expected it to just give it a null value on it’s own and keep running.

I guess I still have a PERL mindset and I will have to get away from that. It may take a little work and just being more careful. Anyway, thank you to both of you. It really is appreciated.
Jim