Re: C/GTK question

[John Vetterli <jvetterli linux ca>]

On Thu, 15 Jun 2006, Matías Torres wrote:
> ... This is what i did:
>
> global.c
>                                               GtkWidget *mainWindow
>
> gtkarch1.c           gtkarch2.c          gtkarch3.c           gtkarch4.c
> /* Al this files uses the mainWindow variable, this is what i do:
> gtkarchX.c
>      #include global.c
>      GtkWidget *mainWindow */
>
> ant then the main.c file which looks like this:
>
> main.c
> #include "gtkarch1.c"
> #include "gtkarch2.c"
> #include "gtkarch3.c"
>
> But the compiler gives me an error, which I understand but i don't know how
> to solve it, that says that i'm redefining the variables declared in
> global.c in each gtkarchX.c
>
> So............ Help? please?

You need to use the "extern" keyword.  Each time you have

        GtkWidget *mainWindow;

in your source, you are instructing the compiler to create a new variable 
called mainWindow.  What you need to do is to use

        extern GtkWidget *mainWindow;

which tells the compiler that the variable called mainWindow exists 
somewhere, somewhere else the program.


Also, a good technique is to put common declarations in a header file.  I 
would suggest creating a file called "global.h", which contains:

        extern GtkWidget *mainWindow;

Then include "global.h" in every source file which needs to access your 
global variable.  Don't forget to actually create the variable in one of 
your source files (i.e. use "GtkWidget *mainWindow" without the "extern" 
once and only once).


HTH
JV