Global Variables over several functions

[lth2h]

I've defined several functions all of which need the same 6 global variables. Now I could put a global statement in each function, but is there a way I can just say once that these variables are global for all functions?

Thanks

[amcgrath]

Not that I'm aware of, but you could write a function that returns an array of these vars and call that function from within all the other ones....

[ayzee01]

What about using the HTTP GLOBALS array method??

And if you put all of your functions within an include file and call that file from each page, cant you just declare all of your variables as global at the top of the include file and then they can be accessed by each individual function????

Mmmm, tricky one

[mithril]

Nope. Global vars should be avoided at all costs. If this isn't possible, they should always be declared global within each function which needs to access them. Don't rely on php.ini settings or functional work-abouts, that's a really bad design practise that leads to bad and non-portable code. There's no if's, and's, or but's about it..... that's just the way it is.

Being a very loosely typed language, all variables are by default global in within the script's scope. Only the function names are global within the script's scope..... a function's inner mechanic's are not in the script's scope. Therefore, a global declaration is required. Christ, think what a mess it'd be if all variables were globally accessible within all functions.

Globals can very quickly make your script's start doing weird and unexpected things (over-writting variables, changing expected values, etc.). There's no way around this, but by specifically declaring which vars will be global you are at least forcing some thought into the application's design..... and hopefully minimizing the number of errors in the process.

In this case, think of functions as a weakened version of OO. On of the strongest characteristics of OO is data encapsulation, and you wouldn't try to over-ride that would you? To a lesser degree, keeping function vars in a different scope than the main script is also data encapsulation (of a sort). Don't muck with it unless you absolutely have to.

If you have to pass a given variable into a function, instead of globalizing it... pass it as an optional variable at the end of your arg's list. For example, you've got a function that accepts 3 arg's and must have access to the HTTP_SERVER_VARS array. Do this:

  function myFunction($arg1,$arg2,$arg3,$serverVars=$HTTP_SERVER_VARS) {

Your call to the function is unchanged:

  myFunction($arg1,$arg2,$arg3);

and the contents of the HTTP_SERVER_VARS array is passed into the function without the need of ugly globals.

Globals are mostly bad, all of the time. Avoid using them as much as possible, but if you must use them take the time to properly plan and declare them.

-geoff

[[deleted]]

"pass it as an optional variable at the end of your arg's list."

'optional arguments' are yet another example of bad practice.

Also, the example you put in your post will not work because PHP does not let you use vars as default values, only strings, numbers and constants. (besides which, $HTTP_SESSION_VARS is not in the function's scope at that point)

[mithril]

You're quite correct about the $HTTP_SERVER_VARS pass borking the function.... brain wasn't engaged when I wrote that.

I'd put forth though that since it's being passed as an arg it matters not that it's not in the functions scope (enters scope during pass).... however that's all academic since it doesn't work anyways🙂

You're right, optional arguments are not good practise. I'd consider them to be better practise than global's though. Best practise is of course to pass everything in as a non-optional argument.

-geoff

[[deleted]]

<nit-picking mode>

"I'd put forth though that since it's being passed as an arg it matters not that it's not in the functions scope (enters scope during pass).... however that's all academic since it doesn't work anyways🙂"

It doesn't enter the scope during the pass, because the 'parameter definition' part is already inside the function's scope, so HTTP_* is not available there at all.
</nit-picking mode>

Globals should indeed be avoided at all costs.

The very reason why you use a function is to make a seperate unit of code that does it's business without interfering with the main script. Using globals in functions draws the function's code right back into the main script's mess.