Global object in library for Arduino - c++

Question

I have a code structure like this
myobj.h
#pragma once
struct myobj {
myobj();
...
} Myobj;
myobj.cpp
#include "myobj.h"
myobj::myobj() { ... }
...
mysketch.ino
#include "myobj.h"
Myobj.someMethod();
...
I understand this won't work because Arduino IDE compiles each file separatedly, so #pragma once won't help me to avoid the multiple definition error (Myobj was created twice) in the linking phase.
I'd like not to bother the user of my future library to create the global object by himself (the object will be used as singleton anyway). The working idea was to use macro:
myobj.h
#pragma once
struct myobj {
myobj();
...
};
#ifndef _MYOBJ_
myobj Myobj;
#endif
myobj.cpp
#define _MYOBJ_
#include "myobj.h"
myobj::myobj() { ... }
...
But then I have to remember to define this macro everywhere but in the ino file. It would be nice to detect that the myobj.h is included in the .ino file with setup and loop function. Is such detection possible without adding any extra code in that ino file? Is there any other way to define global object in library?
When I look into other libraries (like Servo), global object is created in the ino example. I can live with that, but there are objects like Serial that is auto-created somehow, I wonder how.

Answer 1

Ah, I found the solution in the SD library: one clever extern keyword!
myobj.h
#pragma once
struct myobj {
myobj();
...
};
extern myobj Myobj;
myobj.cpp
#include "myobj.h"
myobj::myobj() { ... }
...
myobj Myobj;
mysketch.ino
#include "myobj.h"
Myobj.someMethod(); // works, no multiple definition error
...