Multiple definition error on variable that is declared and defined in header file and used only in its cpp file

Question

I\'m in the process of moving code written to be compiled for one chip onto another chip.

One issue that\'s come up is a multitude of multiple definition errors. Some of

Answer 1

The error goes away if I declare it as extern and define it in the cpp file,

The issue is that even when include guarded etc. the variable gets created once in each compilation unit - but since it is global it is pointing to same variable.

To overcome this is issue you need to either create it in anon. namespace

Something.h

namespace {
  int foo = 0;
}

Or, use the static keyword

Something.h

 static int foo = 0;

Both will create a different variable in each compilation unit.