Access issue regarding static variable [duplicate]

Answer 1

The error you are getting is a linking error not a compilation error.
The linker tells you that it cannot find definition of Class1::var1

You just declared the vector member but did not define it.
Add:

std::vector<bool> Class1::var1;

to only one of your cpp files.

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Good Read:
What is the difference between a definition and a declaration?

Answer 2

Look a little more closely at your class definition. You'll notice it has no access specifiers.. which means all class access defaults to.. private.

Making something static does not imply that it is 'public'.