[openbeos] Re: broken struct mouse_map in InterfaceDefs.h

Could binary compatibility happen ? 
For example, sizeof(struct mouse_map) won't be equal in R5 and OBOS R1 with 
this.

I think the best you can get is source compat. 

Cheers,
Jerome

Selon Andrew Bachmann <shatty@xxxxxxxxxxxxx>:

> Oops,
> 
> Looks like I lose in at least 2 ways:
> 
> Way #1: no R5 compiler supports anonymous structs as union members.
> Way #2: anonymous unions in structs are C++ feature and will not
> compile in C
> 
> So, for future reference all: no anonymous unions in structs in any
> headers that are supposed to be C friendly.
> 
> In my searchings on this issue I also found a warning about interchanging
> access to union members. (that is to say, using a union as a
> reinterpretation
> of the members.)  Apparently the spec doesn't require such things to work
> in the way you expect.  Even on a C++ compiler that supported what I
> wrote earlier, for example, middle could be mapped to button[0] instead
> of button[2] as one might expect.
> 
> I think we have to use separate structs.  Any other suggestions?
> 
> Andrew
> 
> "Andrew Bachmann" <shatty@xxxxxxxxxxxxx> wrote:
> [snip]
> > I think this is at least a source compatible version:
> > 
> > struct mouse_map {
> >     union {
> >             struct {
> >                     uint32 left;
> >                     uint32 right;
> >                     uint32 middle;
> >             };
> >             uint32  button[B_MAX_MOUSE_BUTTONS];
> >     };
> > };
> > 
> > This still has a binary compat problem.  A better alternative
> > would seem to be to use a new struct.
> >

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