global variables

[Anon]

I've heard the talk about how global variables are a bummer , however what I haven't yet heard is why. Can anyone say why?

Later on,
morpheus()

[rdhatt]

It's all about good coding discipline.

If you're only used to coding in PHP then it's understandable why wondering are global vars "bad". PHP is very unstrict and most scripts aren't much more than a few hundred lines. Using a global namespace makes everything easy.

However, in large software applications - especially ones with multiple developers, thousands of lines of code and ones with reusable code global vars can cause distaster. Everyone would have to keep track of the global var so they don't accidently overwrite the values inside them. Avoiding globals var insures you won't be screwing up someone else's code.

[[deleted]]

Indeed.
The main problem of using globals is that it's very difficult to find out where they are used, and what they are used for.

Imagine this:

$sMyGlobal = "apples";
$sBananas = "bananas";

fckMeUpScotty();

echo $sMyGlobal;

and when you run it it outputs "bananas"....

Can you tell what fckMeUpScotty() does to any of the variables?
No you can't.
So you have to look at the function, which is included from a file 354 directories further down the filetree:

function fckMeUpScotty()
{
global $sMyGlobal;
global $sBananas;
$sMyGlobal = $sBananas;
};

See how confusing it can be?
Imagine doing that with 40 scripts and 200 functions.

TIP: Only use globals to contain READ-ONLY data, like configuration data, database names, HTML-style colors etc. Things that you only read from, but NEVER write to.

Always make your function so that they return their output either through the return-value or through the function parameters.

[Anon]

Thanx guys! This is just what I needed to hear. I've been getting away from anyways since they seem to just make a mess, but I needed to understand some of the reasons for the comments.

Thanx again, I appreciate it,
morpheus()