How to declare global variable outside a class?

[babygal]

How to declare global variable outside a class?

[tbscope]

Create a header with global definitions.

Example: my_globals.h

#ifndef MYGLOBALS
#define MYGLOBALS
 
int variable1;
 
#endif

#ifndef MYGLOBALS
#define MYGLOBALS

int variable1;

#endif

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Include the header everywhere you want.

[toutarrive]

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.

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

// globalvar.h

#ifndef MYGLOBALS
#define MYGLOBALS

extern int variable1;
extern int variable2;

#endif

...

// globalvar.cpp implementation

int variable1= 0;
int variable = 0;

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