referring to a class from another file with the scope operator (::) - c++

Question

I have a main.cpp file, with #include "engine.h" in the beginning.
Inside engine.h there's
#include "myObject.h"
namespace nmspc{
MyObject obj1;
//some code here
}
and myObject.h has:
#include <iostream>
class MyObject{
public:
void helloWorld(){
std::cout << "Hello, World!" << std::endl;
}
}
Why can't I refer have in my main.cpp something like this?:
int main{
nmspc::obj1::helloWorld();
return 0;
}
instead I have to type either nmspc::obj1.helloWorld(), or MyObject::helloWorld(). But I'd like to use the one above.

Answer 1

You can do something like this using static member functions, by adding the keyword static before the method declaration. if you do this, the function will not be associated with an actual instantiation of the class, so cannot access any member variables or non-static member functions.
In general, you wouldn't access static member functions through the created object, but through the class name (although it is possible to call it through an instance).
class MyObject{
public:
static void helloWorld() {
std::cout << "Hello, World!" << std::endl;
}
}
int main{
MyObject::helloWorld();
return 0;
}
Whether or not you should do this is dependant on the context. Your program is simple enough that's its not immediately clear why you would make it a static member function, rather than a free function, but I'm not sure I have enough context to give advice.

Answer 2

1st of all
incorrect header content
#include "myObject.h"
namespace nmspc{
MyObject obj1;
//some code here
}
this should be in a cpp module i.e: a translation unit
as it is an instantiation i.e. a dynamic related thing (run time affect code)
whereas header is the place for all of the static related content
if like to write MyObject::helloWorld()
may have it here
myObject.h :
#include <iostream>
namespace nmspc{
class MyObject{
public:
void helloWorld();
};
MyObject::helloWorld(){
std::cout << "Hello, World!" << std::endl;
}
}
because :: (scope resolution op.) is what name space or class/struct referred to
e.g. nmspc::MyObject::helloWorld
might be helloWorld class inside MyObject class belong to nmspc name space
might be helloWorld class belong to MyObject name space belong to nmspc name space. etc
int main{
MyObject obj1;
//some code here
nmspc::obj1.helloWorld();
return 0;
}