Question

I have a class Class1 in some header file Class1.hpp

 class Class1
 {
   static std::vector<bool> var1;
   func();
  }


func()
{
 var1.clear();
 int t=0;
 do
 {
   var1.push_back(t++);
 }while(true); //its some condition

Now inside another function main() in another class in another file, i am assigning var1 to another std::vector like:

 std::vector<bool> var2=Class1::var1;

When I am doing this its giving me the error:

undefined reference to Class1::var1

I am not getting what am I doing wrong. Can someone be kind enough to help in rectifying the error?

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?