Hello Nico ,Peter,
Thanks for posting your views.I was going through a code fragment.
Later I checked the complete code and the usage was :
typedef enum {False, True} boolean;
boolean PLL_lock;
if(PLL_lock==True)
....
which was as Nico's example.
Could you help out with some more clarifications ?
Since PLL_lock is now being used as a variable , would this have a
memory size and how much would that be?
Peter's example on typedef needs some clarification too :
He wrote :
"
typedef int i, *ip, (*vfi)(void);
We can now use the typenames to declare objects...
i my_int;
ip my_int_pointer;
"
My query is why this is interpreted as :
ip my_int_pointer; (my_int_pointer is pointer to integer ??)
and not :
*ip my_int_pointer; (my_int_pointer is integer ??)
Is this because of the ANSI C standard ?
typedef int i;
typedef int* int_pointer; // is straightforward!!!
Cheers
Thomas
--- In [email protected], "peternilsson42" <[EMAIL PROTECTED]>
wrote:
>
> "Nico Heinze" <grollnar@> wrote:
> > "thos_fernando" <thos_fernando@> wrote:
> > > I came across a C statement as below.
> > > typedef enum {False, True} boolean;
>
> That is not a statement, it's a declaration.
>
> > > I was wondering if someone could explain how this would
> > > work,preferably with an example.
>
> How did it work in the code where you saw it?
>
> > > I know that
> > > typedef enum {False,True}; would mean that False=0 and
> > > True=1.
>
> [It would mean that even without the typedef keyword.]
>
> > > How does the word boolean play a part ? AFAIK boolean is
> > > not a C keyword. How would this be used while programming?
> >
> > ... The "typedef" keyword tells the compiler that from this
> > point onward (subject to scope rules, but that's a different
> > matter) the term "boolean" will always mean "enum {False,
> > True}". "typedef" is used to create a new name for a
> > particular type.
> >
> > An easy example: Usually in C you would have to write
> >
> > enum {False, True} flag1;
> > enum {False, True} flag2;
> > enum {False, True} flag3;
>
> Since that isn't C, I don't see why I would usually have
> to write it that way! :-)
>
> I may write it as...
>
> enum boolean { False, True };
>
> enum boolean flag1;
> enum boolean flag2;
> enum boolean flag3;
>
> > now with this new name for the type you can simply use:
> >
> > boolean flag1;
> > boolean flag2;
> > boolean flag3;
> >
> > which makes your code easier to read (and safer against some
> > typos).
>
> Typedef is a way of saying, don't create objects, create type
> names.
>
> Consider this declaration...
>
> int i, *ip, (*vfi)(void);
>
> Here we create objects with the types: int, int *, and pointer
> to a function taking no parameters returning an int.
>
> If we put typedef at the front of the declaration, we change
> to the declaration to mean declare type names instead of
> objects...
>
> typedef int i, *ip, (*vfi)(void);
>
> We can now use the typenames to declare objects...
>
> i my_int;
> ip my_int_pointer;
> vfi my_pointer_to_function_returning_int;
>
> You can't do this with every object delcaration, but it's
> a good way to think of how typedef works.
>
> As an aside, the peculiar implementation of typedef in the
> grammar means that you can make some wierd, but perfectly
> valid declarations...
>
> struct node { struct node *next; int i } typedef node_t;
>
> --
> Peter
>
