Re: learning dragonfly or C...

[Garance A Drosihn <drosih@xxxxxxx>]

At 1:58 AM -0500 11/11/04, George Georgalis wrote:
> I have a general idea about the use of pointers, but don't really
> understand how they are used. What exactly does this syntax mean?
>
>         struct vnode **vpp, *vp;
>         vpp = &vp;

You may find it helpful to install the port called 'cdecl'.
It can help to explain declarations (although it will not
help with executable statements, such as the second line).

E.g.:
      (3)  cdecl
      Type `help' or `?' for help
   -  explain struct vnode **vpp;
      declare vpp as pointer to pointer to struct vnode

The "explain" command is what you type in, and the following line
is what `cdecl' replied with.  `cdecl' does not know everything
about the C language, and in particular you can only ask it to
explain a single declaration at a time.  It will give an error
message for:
      explain struct vnode **vpp, *vp;

even though that is completely valid C.  So, it is not a magic
know-all utility, but it can be helpful if you are new to C.
Note that it also helps when going from an english description
into a valid C declaration, so you can enter the *command* of:
      declare vpp as pointer to pointer to struct vnode
and `cdecl' will reply with:
      struct vnode **vpp

This helped when I was coming from a systems-programming language
called *Plus, which was similar to Pascal/Algol in many ways.

--
Garance Alistair Drosehn            =   gad@xxxxxxxxxxxxxxxxxxxx
Senior Systems Programmer           or  gad@xxxxxxxxxxx
Rensselaer Polytechnic Institute    or  drosih@xxxxxxx