Hello, everyone.
I'm having trouble understanding the bottom of page 223. It says when using include files we have to guard against calling on the same function twice. It offers a solution - some code to guard against the problem.

... declare a variable in every include file you create:
$COMMON_INCLUDED=1;

and then test for it at the beginning of the include:
if (!$COMMON_INCLUDED) $COMMON_INCLUDED=1;

I don't understand this very well. Could someone please explain this to me? Does this mean that each file you include should have $COMMON_INCLUDED=1; in it? I don't understand what the 2nd line of code does or what it means.

Any help would be greatly appreciated.

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An overworked Web Developer who\'s expected to know everything yet given time to study nothing.

That looks strange to me too. I think they want the include file to have a variable (they're using a name similar to the file here) that is set to a one within the include file. They then test to see if that variable has been set true, meaning it's been included already.

I think they meant to write in that second line:
if (!$COMMON_INCLUDED) include("common.inc");

Oregon

Thanks for the reply. I was scratching my head for the longest time trying to figure out how that line of code in the book helped anything. I'm going to look over your code sample again and see if I can come to grips with this issue.

I suppose you could also test for the $COMMOM_INCLUDED variable upon entry into the include file. If the file HAS been included already, you could just bypass the functions, like with a big IF statement within the include file.
I guess you already know that the '!' used before a variable means "if not true (ie isn't set)". Anyway, good luck!

Oregon