Re: Forward declaration is not possible

[Atakan Gurkan <ato at northwestern dot edu>]

On Tue, Dec 17, 2002 at 05:13:19PM +0100, Peter Haase wrote:
> Hi Brian,
> I'm writing a library*  that provides some functions that are useful for 
> developing simulation programs. For that reason I programmed a class called 
> RandomGenerator:
> 
> //in myrandom.h:
> #include <gsl_rng.h>
> 
> class RandomGenerator
> {
[deleted]
> };
[deleted]
> 
> //in myrandom.h:
> // !This isn't needed anymore: #include <gsl_rng.h>!
> 
> //Forward declaration:
> struct gsl_rng;
> 
> class RandomGenerator
> {
[deleted]
> };
>  
> Unfortunatley this forward declaration is not possible if gsl_rng is declared 
> as follows:
> 
> typedef struct {
>   char* name;
>    /*... */
> } gsl_rng;
> 
> but the forward declaration is possible if gsl_rng is declared as follows:
> 
> typedef struct gsl_rng {
>   char* name;
>   /*... */
> } gsl_rng; 
> 
> Note, that code that is already existing can be used with that declaration as 
> it was before! I'm not shure if it is strict ANSI C to use gsl_rng as a name 
> for the struct and as the name of the new type introduced by the typedef 
> statement. But at least in C++ it is standard conform (see C++ ARM s. 106): 
> 'A typedef may be used to redefine a name to refer to the type to which it 
> already refers - even in the scope where the type was originally declared. 
> For example: 
> typedef struct s { /* */ } s;'
> 
> *(actually I'm not writing a library, but I think that is a more common case. 
> So look to it as an abstract example)
> 
> Hope this makes it a bit more clearer, what I would like to do.
> 
> Thanks,
> Peter
Hi,
First, my apologies in advance if I am wrong. I did not actually try the idea
that I am about to suggest. Why can you not do something like:
typedef struct gsl_rng gsl_rng_typedefed;

and then use gsl_rng_typedefed for your C++ class? 
I do not mean to object to your proposed change, I have no idea what the 
consequences of that would be, I am just trying to suggest a way for you to get 
things going.

cheers,

ato