You could simply use M_PI from the <math.h> include (there are other constants too).

A direct solution to your question would be:

globals.h:

double g_pi; 

globals.c

g_pi = 3.; 

For all other .c and .h files:

extern double g_pi; 

Also see wikipedia

You could simply use M_PI from the <math.h> include (there are other constants too).

Edit: your setup is correct. I got a working minmal example:

globals.h

extern double g_tst; 

globals.cpp

#include "globals.h" double g_tst = 4.0; 

main.cpp

#include "globals.h" #include <stdio.h> #include <stdlib.h> int main() { fprintf (stderr, "g_tst = %lf \n", g_tst); return 0; } 

The problem is within your buildsystem

See wikipedia

You could simply use M_PI from the <math.h> include (there are other constants too).

A direct solution to your question would be: globals.h:

double g_pi = 3.; 

For all other .c files:

extern double g_pi; 

Also see wikipedia

You could simply use M_PI from the <math.h> include (there are other constants too).

A direct solution to your question would be:

globals.h:

double g_pi; 

globals.c

g_pi = 3.; 

For all other .c and .h files:

extern double g_pi; 

Also see wikipedia