First, define a named type:

typedef union
	{
	unsigned int	uint;
	signed int	ssint;
	unsigned char[2] unchar
	} mytype_t;


Second, declare and implement the function correctly. It is not allowed
to declare a parameter without type:

void myDumbFunction( mytype_t somevar )
	{
	if( somevar.unchar[1] )
		do_something();
	}


Third, declare a variable with the correct type, initialize it and call
the function:

mytype_t    dumbvar;

// (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;

myDumbFunction( dumbvar );


Best regards,

Isaac



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; unsigned
> 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 that
> 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 real
> 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
>

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