Best way of declaring global variables?

Question

I have an OpenGL application which requires the use of a vector in more than one OpenGL function. As far as I know the best way of dealing with this is to declare the vector in a header file, and include the header file in all the files containing the OpenGL functions.

The problem is that I get a multiple definition error at the linker stage. What is the best solution to this? Is there a better way of doing it without globals?

Learn the difference between definition and declaration. Declare the vector in a header file. Define the vector in a single source file. — chill, Dec 01 '12 at 13:03
I doubt you actually need a global. What's wrong with passing it around as argument? — , Dec 01 '12 at 13:09
delnan, you cannot pass your own arguments into OpenGL functions! — FreelanceConsultant, Dec 01 '12 at 13:21
What do you mean by OpenGL function then? As far as I know, OpenGL defines no callbacks. Are you talking about GLSL shaders? There's `uniform` for that. — , Dec 01 '12 at 13:36

SomeWittyUsername · Accepted Answer · 2012-12-01T13:23:02.073

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Define your vector in one of the implementation files and declare it as extern in rest of the places where it's needed or in header file.

In most cases globals are not the way to go, but without having a look at the overall design no one can tell for sure what's the best for your situation.

edited Dec 01 '12 at 13:23

answered Dec 01 '12 at 13:03

SomeWittyUsername

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Okay thanks, how do I go about doing this? After the header file containing my class, do I declare a vector of classes with the extern keyword? – FreelanceConsultant Dec 01 '12 at 13:05
Yes. And make sure to make a **single** definition in one of the implementation files – SomeWittyUsername Dec 01 '12 at 13:07

score -3 · Answer 2 · answered Dec 01 '12 at 13:38

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the other way is to use Singleton pattern

answered Dec 01 '12 at 13:38

vurtne.ye

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I got commented by @JonSkeet for suggesting that... And not with a positive message... – ppeterka Dec 01 '12 at 14:06
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@ppeterka I'd be fairly sure he'd more politely than I. – thecoshman Jul 21 '14 at 19:14

Best way of declaring global variables?

2 Answers2