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Re: Quesition about Lisp_Vector

From: Andreas Schwab
Subject: Re: Quesition about Lisp_Vector
Date: Fri, 11 Nov 2011 09:59:53 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux)

Qiang Guo <address@hidden> 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 Schwab, address@hidden
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