The purpose of the reserved fields in many internal structures

[José Alburquerque-3]

Sorry to ask this question because it's more a "learning" question than
anything else.  If it's not really important please ignore the question.

Would someone be able to tell me why (I'm only asking out of curiosity)
many internal structures (like GstMiniObject) have a "reserved" field
generally called "_gst_reserved".  Thanks.

--
José


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[Sebastian Dröge-7]

On Sun, 2010-02-07 at 19:45 -0500, José Alburquerque wrote:
> Sorry to ask this question because it's more a "learning" question than
> anything else.  If it's not really important please ignore the question.
>
> Would someone be able to tell me why (I'm only asking out of curiosity)
> many internal structures (like GstMiniObject) have a "reserved" field
> generally called "_gst_reserved".  Thanks.


It's there to allow later additions to those structures without breaking
ABI. Look at GstBus' instance struct for example.

Without these reserved areas, additions to the structures would change
their size, which would require recompilations of everything using them.
In the case of the instance/class structs all subclasses' instance/class
structs would increase in size too.

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[José Alburquerque-3]

On Mon, 2010-02-08 at 08:31 +0100, Sebastian Dröge wrote:
> It's there to allow later additions to those structures without breaking
> ABI. Look at GstBus' instance struct for example.
>
> Without these reserved areas, additions to the structures would change
> their size, which would require recompilations of everything using them.
> In the case of the instance/class structs all subclasses' instance/class
> structs would increase in size too.

Thank you.  I suspected as much but wanted a definite confirmation of
what I suspected.

--
José



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