From: Richard Nichols <tiberius AT mailhost DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: packed?
Date: Fri, 09 Jan 1998 19:15:31 +1000
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David Eberhard wrote:
> 
> I have been going over some source code for a linear-frame buffer and
> in the source code, the author used some attribute called pack.  What
> is this?  Here's some of the code:
> 
>    #define PACKED __attribute__ ((packed))
>    #pragma pack(1)
>    /* SuperVGA mode information block */
>    typedef struct {
>       short   ModeAttributes PACKED;         // Mode attributes
>       char    WinAAttributes PACKED;         // Window A attributes
> --snip--
>    #pragma pack()
> 

this tells the compiler not to align the data to dword boundaries
otherwise the above would be in RAM:
    typedef struct {
       short   ModeAttributes PACKED;         // Mode attributes
(2 bytes padding)
       char    WinAAttributes PACKED;         // Window A attributes
(3 bytes padding)

and when a int returns data in the struct you don't want any bytes
in the way which aren't supposed to be there. This can of course
make your program a little slower..

-Rich

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