How to declare global variable outside a class?

How to declare global variable outside a class?

Create a header with global definitions.

Example: my_globals.h

Code:

---

#ifndef MYGLOBALS
#define MYGLOBALS
 
int variable1;
 
#endif

---

Include the header everywhere you want.

Use extern keyword to avoid allocating some memory for yours global variables every time you include your header globalvar.h in multiple files. With this keyword you only allocate them once.

Code:

---

// globalvar.h
 
#ifndef MYGLOBALS
#define MYGLOBALS
 
extern int variable1;
extern int variable2;
 
#endif
 
...
 
// globalvar.cpp implementation
 
int variable1= 0;
int variable = 0;

---