Thanks Isaac and everyone else for the great replies. I'm going to try
it and see what the disassembly looks like!

Best regards,

Bob

On Wed, Jan 16, 2013, at 05:44 PM, Isaac Marino Bavaresco wrote:
> First, define a named type:
>=20
> typedef union
> 	{
> 	unsigned int	uint;
> 	signed int	ssint;
> 	unsigned char[2] unchar
> 	} mytype_t;
>=20
>=20
> Second, declare and implement the function correctly. It is not allowed
> to declare a parameter without type:
>=20
> void myDumbFunction( mytype_t somevar )
> 	{
> 	if( somevar.unchar[1] )
> 		do_something();
> 	}
>=20
>=20
> Third, declare a variable with the correct type, initialize it and call
> the function:
>=20
> mytype_t    dumbvar;
>=20
> // (in your example you used an "unsigned int" variable as argument, so
> we will initialize the field of the same type)
> dumbvar.uint    =3D somedumbvalue;
>=20
> myDumbFunction( dumbvar );
>=20
>=20
> Best regards,
>=20
> Isaac
>=20
>=20
>=20
> Em 16/1/2013 22:01, Bob Blick escreveu:
> > Is this a correct way to declare and call a function that uses a union
> > as the argument, and pass it a value that is not declared as union?
> >
> > //declaring the function
> > void myDumbFunction(union {unsigned int uint; signed int ssint; unsigne=
d
> > char[2] unchar});
> >
> > // calling it from somewhere in my program
> >   unsigned int dumbvar;
> >   dumbvar =3D somedumbvalue;
> >   myDumbFunction(dumbvar);
> >
> > // the function
> > void myDumbFunction(somevar){
> >   if (somevar.unchar[1])
> >     do_something();
> > }
> >
> > Is that going to work, the compiler should know that somevar is an
> > unsigned int(not that it should matter since it's just memory space tha=
t
> > is the size of the union), so within my function I can access
> > somevar.uint somevar.ssint as well as somevar.unchar[0] and
> > somevar.unchar[1]
> >
> > That all seem OK? I know that in most cases using a union serves no rea=
l
> > purpose other than to be dangerous, there are other ways to do things.
> > But my question is whether this is accurate or how it would be made
> > correct if it isn't.
> >
> > Thanks,
> >
> > Bob

--=20
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