External Variables

[Bart C]

Suppose I have two modules A and B, and I want them to share the same
variable X.

X might be defined in A but I want to declare it in B as well.

How would I do that in C language?

For functions, I can define it in A and a declaration can be put into a
shared header. But how do I do a declaration of a variable that is defined
elsewhere?

(I can do a workaround using pointers but I'd like direct access)

Thanks, Bart

 

[Mike Wahler]

Suppose I have two modules A and B, and I want them to share the same
variable X.

X might be defined in A but I want to declare it in B as well.

How would I do that in C language?

For functions, I can define it in A and a declaration can be put into a
shared header. But how do I do a declaration of a variable that is defined
elsewhere?

(I can do a workaround using pointers but I'd like direct access)

Look up 'extern'.

-Mike

 

[Richard Tobin]

Suppose I have two modules A and B, and I want them to share the same
variable X.

X might be defined in A but I want to declare it in B as well.

How would I do that in C language?

For functions, I can define it in A and a declaration can be put into a
shared header. But how do I do a declaration of a variable that is defined
elsewhere?

Exactly the same way. Declare it in the header as "extern whatever X;"

For functions, you don't have to say "extern" (because the absence of
a definition makes it unambiguous), but I generally use it anyway.

-- Richard

 

[pete]

Suppose I have two modules A and B, and I want them to share the same
variable X.

X might be defined in A but I want to declare it in B as well.

How would I do that in C language?

/* BEGIN a.c */

#include "a.h"

int X;

/* END a.c */



/* BEGIN a.h */

extern int X;

/* END a.h */



/* BEGIN b.c */

#include "a.h"

/* END b.c */