Re: Identifying a structure by reading it's first field.

[Osmo Antero <osmoma gmail com>]

Very good.
This makes code much cleaner because I do not have to send around both the
type field and node separately. Now I simply

void func(gpointer node) {

   switch (NODE_TYPE(node)) {
      case TYPE_1:
              ...
      case TYPE_2:
              ...

    }
}

// Osmo Antero

On Sat, Jun 2, 2012 at 6:04 AM, Ernie Wright <erniew comcast net> wrote:

> On 6/1/2012 2:17 PM, Osmo Antero wrote:
>
> > I have couple of C structures that I want to distinguish between by
> > reading the structures' first (type) field.  [...]
> >
> > Q:  Can I assume that the "type" field is always first in the
> > structures, so I can read it with: NodeType type = *(NodeType*)node;
>
> Yes.  Structure members are stored in the order in which they're
> defined, and a pointer to a structure also points to its first member
> (suitably cast).  This is guaranteed by the C standards.
>
> > but can I trust it on all *nix plattforms and GCC compilers.
>
> Anything that's standards-compliant.
>
> - Ernie                                  http://home.comcast.net/~erniew
>
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