#ifndef MYAPP
#define MYAPP
#include <map>
namespace MyApp{
    class MyClass{
        private:
            static std::map<int, bool> SomeMap;
        public:
            static void DoSomething(int arg);
    }
}
#endif MYAPP

#include "Header.h"
#include <map>
namespace MyApp{
    void MyClass::DoSomething(int arg){
        if(MyClass::SomeMap[5]){
            ...
        }
    }
}