Question

I tried many solutions, but can’t get my program work.

main.h

short NWMP_acc[3];
short NWMP_gyro[3];

main.cpp

printf_( "%i,%i,%i, g\n", NWMP_gyro[YAW],NWMP_gyro[PITCH],NWMP_gyro[ROLL]);

other.cpp

#include "main.h"
NWMP_gyro[YAW]   = (((buf[3]>>2)<<8) +  buffer[0]);//multiple definition of `NWMP_gyro'

If I change to “extern short NWMP_acc[3];” than I get an error “undefined reference to `NWMP_acc'”

Answer 1

You need both with and without the extern

In your header you need:

extern short NWMP_acc[3];
extern short NWMP_gyro[3];

But in one of your “.cpp” files you still need:

short NWMP_acc[3];
short NWMP_gyro[3];

The reason for this is that the extern keyword can be roughly thought of as meaning “I promise that somewhere in one file there exists an actual real thing that looks like this”.