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# Globals

## 13 posts in this topic

Some time ago I worked on a (professional) project in which I was surprised to see quite a lot of globals. There were classes like CRender, CPhysics, CClient and so on, and there was file globals.h that tied together all these classes by declaring GRender, GPhysics, GClient. Now, the entire code relied upon these globals and often even a small change in gpu texture class header caused recompilation of a big part of the codebase (which was medium in size but the total recompilation time was around 1 min).

We've heard all these stories about globals being bad and personally I prefer to write code a different way but I must say that working with all these globals was very easy - where ever I was in the code I could always easily access the client's, render's and so on, properties.

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Didn't know the locator pattern before. Sounds like a nice idea although... in itself it needs a global variable :). Or be implemented as a singleton. But hey, can't we just implement CRender, CClient and CPhysics as singletons in the first place? Instead of declaring them global why not just have them declared in their respective files?

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Almost every time I am lazy and make something a global, I end up eventually needing to make it non-global.

I'm also not a big fan of the service locator pattern, though I do use it in places. It makes it hard to understand the dependencies, and you can only have one of a particular service.

Best to just declare/pass down dependencies explicitly in most cases.

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Multithreading with globals is also a very dangerous thing.

If all your data resides in isolated blobbs of object instances, you can be very sure that you can churn through each blobb in a seperate thread without any risk of race conditions. But if you use globals, you have that single data point that is accessed by all blobbs which prevents you from easily parallizing stuff.

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I don't think the ease of access is worth the messy code you'll wind up with when the project gets rolling. Granted it can be a pain when you have to go back and edit your constructors to pass in variables you forgot about earlier, but things make so much more sense when only having access to what you need.

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Recently a nice article showed up, http://www.gamedev.net/page/resources/_/technical/game-programming/a-long-awaited-check-of-unreal-engine-4-r3635 where there are parts of Unreal Engine revealed. And what got my attention was this line in one of the listings:

ENGINE_API UEngine* GEngine = NULL;


It looks like even best of the bests use globals... :)

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Globals are like any other construct that exists in programming. Used well, they are excellent. Used badly, they are the spawn of satan.

I worked for a large company that refused to let developers use global variables, at the time we had 256K of rom for the entire code and 512K of ram.

We would develop a product, ship it, archive the source code, then start on the next product.

Just before shiping we would always have the problem that we were a few K over budget on the rom and there would be a mad panic to optimise everything.

Once I added a single global variable and saved 20K of rom.

For me it's not an issue of should I use globals or not, I will if I need to. It's more a case of do you know enough about the system to know when using a global is safe and an improvement.

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