Spontaneous Constants?

Anon

I want to avoid duplicate function errors caused by including the same
file twice. So I thought I'd try C-style definitions, defining a
constant in each include file. To test it, I defined a constant
CONTROLS_INC in a control file. Then I tried out this simple code:

<?php
if (CONTROLS_INC) {echo "defined<br>"}
include("./controls.inc.php");
if (CONTROLS_INC) (echo "defined<br>"}
?>

That gave me two "defined" strings, even after I commented out the
include line, which puzzled me. So I reduced the code to

<?php echo CONTROLS_INC ?>

which gave the output "CONTROLS_INC"!!! So it seems that any arbitrary
text in php code is automatically defined as a constant, with its name
doubling as the value. OK, I worked around it by testing for a specific
value for CONTROLS_INC but this seems bizarre behaviour to me.

This is using PHP4, btw.

Anon

this seems bizarre behaviour to me.

I've always assumed it was modelled after perl's "barewords". Of course, depending on what you think of perl, this may not cause you to move it out of the "bizarre" category, either...

Anon

Uhm... I might be off.. but the reason you are getting that response is because you are not telling php that its a variable.. ie...

<?php echo $CONTROLS_INC ?>
instead of
<?php echo CONTROLS_INC ?>

or no?

Anon

"<?php echo $CONTROLS_INC ?>
instead of
<?php echo CONTROLS_INC ?> "

No, it's a constant, not a variable.

Anon

Bizarre or not, it's entirely undocumented behaviour. One thing I like about PHP as opposed to (urgh) Python is that PHP is (mostly) internally consistent and predictable, which normally means that I can guess how the bits I haven't used yet will perform. But I'd count that as an entirely unpredictable behaviour.

Anon

Be careful, using an arbitrary "constant" such as CONTROLS_INC is not a functionality, but a programming bug ! When PHP encounters such a thing, it converts it to the corresponding string. I advise everybody to use error_reporting(E_ALL) to detect such a problem. You would have received the following notice :

Warning: 'CONTROLS_INC' is not a valid constant - assumed to be "CONTROLS_INC"

I consider that E_ALL should be the default value in php.ini, which would have avoided tons of bugs in thousands of scripts.

By the way, the proper way to test a constant is use the defined() function :

if(!defined("CONTROLS_INC"))
include("controls.inc");

Anon

Which is what I meant, in a round about way... 🙂

Anon

"I consider that E_ALL should be the default value in php.ini, which would have avoided tons of bugs in thousands of scripts. "

You're right. That would have alerted me right away and made the conversion to a string seem less arbitrary.

Anon

use the new functions

include_once() and require_once() if you have them

they basically will only include the file if it hasnt been already

theyre only available in the very latest versions of php

--harlan

Anon

A 2 second search over at php.net turned up all the documentation you need to correctly use constants.

http://www.php.net/manual/html/language.constants.html

Anon

Mitch Vincent wrote:

A 2 second search over at php.net turned up all the documentation you need to correctly use constants.

I did actually look there, thank you very much. The particular behaviour I asked about in my original post - the fact that arbitrary text in php code is converted into a string constant - is NOT documented on that page or anywhere else in the manual.

Anon

Well, I was refering to constants documentation, that's why the subject was "It's not exactly undocumented" -- meaning that you weren't declaring PHP constants as the documentation says you should..

I meant no offense, just pointing that out for people to look at that want to use constants.

Anon

Mitch Vincent wrote:

Well, I was refering to constants documentation, that's why the subject was "It's not exactly undocumented" -- meaning that you weren't declaring PHP constants as the documentation says you should.

I've read the documentation - it's very sparse. Most importantly, it rarely defines limits - it just says "this works". It's important to know the limits of what you can and can't do - and when you find them, to find out if it's a bug or feature that stops you/lets you do it.

In the absence of good documentation, the only thing to do is try things out.