Apparently there's a lot of variety in opinions out there, ranging from, "Never! Always encapsulate (even if it's with a mere macro!)" to "It's no big deal – use them when it's more convenient than not."
Specific, concrete reasons (preferably with an example)
- Why global variables are dangerous
- When global variables should be used in place of alternatives
- What alternatives exist for those that are tempted to use global variables inappropriately
While this is subjective, I will pick one answer (that to me best represents the love/hate relationship every developer should have with globals) and the community will vote theirs to just below.
I believe it's important for newbies to have this sort of reference, but please don't clutter it up if another answer exists that's substantially similar to yours – add a comment or edit someone else's answer.