Re: Merging changes to volatile bitfield structs

["Phil Endecott" <spam_from_gcc_help_2 at chezphil dot org>]

John Love-Jensen wrote:
> Hi Phil,
>
> > Can anyone share their preferred approach to this sort of problem?
>
> Reg workingReg = reg;
> workingReg.a = 0;
> workingReg.b = 0;
> workingReg.c = 0;
> reg = workingReg;

I'm having trouble working out the necessary casting:

struct S {
  unsigned a : 1;
  unsigned b : 31;
};

volatile S s;

void f() {
  S x;
  x.a = 0;
  x.b = 0;
  s = x;
}

This fails to compile with g++:

$ g++ -W -Wall -c /tmp/voltest.cc
/tmp/voltest.cc: In function â??void f()â??:
/tmp/voltest.cc:12: error: passing â??volatile Sâ?? as â??thisâ?? argument of 
â??S& S::operator=(const S&)â?? discards qualifiers

It does compile as C, if I replace 'S' with 'struct S'.  I have tried 
various casts but haven't yet found the right one.  Any ideas anyone?


Thanks,

Phil.