Re: Quesition about Lisp_Vector

[Andreas Schwab <schwab@linux-m68k.org>]

Qiang Guo <qguo@ualberta.ca> writes:

> Hi, I'm new to devel aspect of Emacs. And I'm having a problem reading
> Emacs source code: in the definition of Lisp_Vector
>  struct Lisp_Vector
>   {
>     EMACS_UINT size;
>     struct Lisp_Vector *next;
>     Lisp_Object contents[1];
>   };
>
> why contents's size is fixed ?

Standard C89 doesn't have flexible array members, so this is using the
well known struct hack.

> And later when actually allocating space
>
>  nbytes = sizeof *p + (len - 1) * sizeof p->contents[0];
>
> I don't understand how this nbytes is calculated. why only (len-1)

Because one element is already included in struct Lisp_Vector.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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