extern and typedef

[-EquinoX-]

Ok, say I have a declaration.h file which inside of it has the following:

extern int lineno;

typedef struct treeNode
{
int lineno;
some other stuffs here
}


and I have another file which is test.c, which wants to use the lineno variable on that declaration.h file. I already include declaration.h on top of the header of test.c, however it still can't find lineno. It gives me an error of:

undefined reference to `lineno'


So what should I do so that I can use the lineno variable? Thanks

[master5001]

You need to actually define

int lineno;

Somewhere in a C file. And inside a structure doesn't cut it. That is a scoped context.

[-EquinoX-]

but the cuts out the main purpose of what I really want, what I want to do is that so that I can reference lineno with whatever is declared for lineno inside the struct it self...

basically so that I can use lineno in any .c file that I want

[master5001]

Right, which isn't something that you are robbed of doing by following the proceedure I just gave you... On a random side note, when did the tabs on my sig get all jacked up?

Puts the global in ONE of your C files.

[-EquinoX-]

if I do :

int lineno in one of my .c file then will the struct that has a lineno inside of it has the same value as lineno in a .c file?

[tabstop]

Of course not. Each object of that struct will have its own lineno variable (which would have to be accessed via object.lineno or objectptr->lineno).

[master5001]

But what you could or maybe even should do is initialize every struct to have a copy of lineno into it.

Or if they need a synchronous copy of lineno you can simply change your design a bit.

Example:

struct treeNode 
{ 
  int *lineno;
  ...
};

And have every struct treeNode->lineno = &lineno;

[MyRedz]

so is int *lineno a pointer which is included in all the struc variable and then is immediately used when the struc is initialized?

[Elysia]

No, it's not.
You should stop trying to make the variable inside the struct refer to the global one.
Essentially, what you want to do is initialize members in the struct before use.
So, I have two suggestions:
1) If you can use C++, do it. Constructors will do exactly what you want there.
2) If you still intend to use C, create a function that creates and/or initializes the struct in the way you want. Then call it.