C++ link error LNK2005

I am new to C++ programing and I'm trying to make a program that simulates Conway's game of life. I'm almost done but when I made each function have it's own file I keep on getting this l开发者_StackOverflowinker error.

1>algorithm_change.obj : error LNK2005: "unsigned short height" (?height@@3GA) already defined in algorithm.obj

My code is at https://github.com/rupertsteel/Life/tree/master/Life

Without looking at the code, do you have a global unsigned short height; in any header file? If yes, replace that with extern unsigned short height; and put a unsigned short height; in a source file that includes the specific header.

A few comments:

1) array_length in life.h needs to be externed

2) All the externed variables (width, height, ticks, count_array, change_array, error_check, algorithm_length, array_length) need to be defined somewhere.

In your code you've basically told the compiler that those variables exist somewhere but haven't actually placed them in existence anywhere. In one of your .cpp files in the global scope you need to put:

unsigned short int width;
unsigned short int height;
unsigned long int ticks;
unsigned short int count_array[10923][10923];
bool change_array[10923][10923];
int error_check;
unsigned long int algorithm_length;
unsigned long int array_length;

Which is exactly the same as what you have in life.h, except without the extern keyword. This will actually create the variables, as opposed to now where they have no concrete implementation.

If you make the changes I suggest your code will compile (tested using gcc). That being said, the actual error you're seeing doesn't make sense.