Weird linker error with static std::map

Question

Why do I get linker error when I try to compile this in Visual Studio 2008

#include 
#include 
#include 

Answer 1

You've declared the static member _myMap, but not defined it. Add this line just above int main():

std::map<int, int> MyClass::_myMap;

Think of it like a function that has been declared but not defined in any .cpp file - you get a linker error if you use it.