Unresolved external symbol on static class members

Question

Very simply put:

I have a class that consists mostly of static public members, so I can group similar functions together that still have to be called from other clas

Answer 1

in my case, I declared one static variable in .h file, like

//myClass.h
class myClass
{
static int m_nMyVar;
static void myFunc();
}

and in myClass.cpp, I tried to use this m_nMyVar. It got LINK error like:

error LNK2001: unresolved external symbol "public: static class... The link error related cpp file looks like:

//myClass.cpp
void myClass::myFunc()
{
myClass::m_nMyVar = 123; //I tried to use this m_nMyVar here and got link error
}

So I add below code on the top of myClass.cpp

//myClass.cpp
int myClass::m_nMyVar; //it seems redefine m_nMyVar, but it works well
void myClass::myFunc()
{
myClass::m_nMyVar = 123; //I tried to use this m_nMyVar here and got link error
}

then LNK2001 is gone.