Keyword to make a variable known over multiple units, but keeping the declaration and initialization local to a file (probably an implementation file (.cpp) )

Example

In the example below there are two integer globals (note: avoid using global data [0] [1] ). The int x is declared and initialized in unit1.cpp, the int y in declared in unit2.cpp and initialized by the locally unknown int x. To read the values of both integers, two getters are put in the header files.

UnitMain.cpp

#include "Unit1.h"

#include "Unit2.h"

#include <cassert>

int main()

{

assert(GetX() == 42);

assert(GetY() == 42);

}

Unit1.h

#ifndef Unit1H

#define Unit1H

const int GetX();

#endif

Unit1.cpp

#include "Unit1.h"

int x = 42;

const int GetX() { return x; }

Unit2.h

#ifndef Unit2H

#define Unit2H

const int GetY();

#endif

Unit2.cpp

#include "Unit2.h"

extern int x;

int y = x; //Seems risky, dependent on module process order

const int GetY() { return y; }

References

[0] Herb Sutter , Andrei Alexandrescu . C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Item 10: 'Minimize global and shared data'.

[1] Herb Sutter , Andrei Alexandrescu . C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Item 18: 'Declare variables as locally as possible'.

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.