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Groups > comp.lang.c > #126879
| Subject | Re: C Construction Problem |
|---|---|
| Newsgroups | comp.lang.c |
| References | <p6h95408re@news4.newsguy.com> |
| From | bartc <bc@freeuk.com> |
| Message-ID | <atWiC.83231$6B6.30628@fx17.am4> (permalink) |
| Organization | virginmedia.com |
| Date | 2018-02-20 14:42 +0000 |
On 20/02/2018 13:51, F. Russell wrote:
> #define peiGetOps(image) (((imageType*)(image))->ops)
> I can't understand the need for these constructions.
To fix the program,
> among other things, I was able to rewrite these as follows:
>
> #define peiGetOps(image) image->ops
So you've dropped the (imageType*) cast which probably isn't needed.
> #define peiGetWidth(image) (*image).width
Note that (*image).width can be written as image->width and vice versa.
> #define peiGetHeight(image) (*image).height
> #define peiGetDepth(image) (*image).depth
> #define peiGetLinebytes(image) image->linebytes
>
> Note that these 5 lines are just a few of many examples of
> this kind.
You do know they are just macros? So:
peiGetOps(X)
in the code gets mapped to:
X->ops
The reason for the macro may have been to incorporate the cast which
would otherwise make things messy. A cast that may not always be needed,
so that it can be removed by redefining the macro, as you have.
>
> But even more puzzling (to me) are the following lines:
>
> #define peiGetConvertSrc(image) (*(imageType**)&(image)->clientData[0])
> #define peiGetConvertOp(image) (*(int32_t*)&(image)->clientData[2])
>
> I can't even begin to deconstruct these. Can someone explain what
> is going on?
A construct like *(T*)&X is type-punning. If X is of type U, then this
interprets it as of type T.
In the first example, T is imageType*, while clientData appears to be of
type int32_t.
(Which sounds wrong; if porting to 64 bits, then pointers are likely to
be 64 bits, but you're interpreting both clientData[0] and the following
clientData[1] as one 64-bit pointer.)
>
> Here is the code for the imageType struct:
>
> struct imageType {
There would need to be a typedef called imageType too.
> int32_t clientData[PEI_CLIENT_SIZE]; };
--
bartc
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C Construction Problem "F. Russell" <fr@random.info> - 2018-02-20 13:51 +0000
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-20 14:42 +0000
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-20 15:06 +0000
Re: C Construction Problem Manfred <noname@invalid.add> - 2018-02-20 18:07 +0100
Re: C Construction Problem Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-02-20 14:54 +0000
Re: C Construction Problem "James R. Kuyper" <jameskuyper@verizon.net> - 2018-02-20 10:06 -0500
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-20 16:11 +0000
Re: C Construction Problem Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-02-20 15:08 +0000
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-20 16:22 +0000
Re: C Construction Problem Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-02-20 17:03 +0000
Re: C Construction Problem Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-02-20 09:23 -0800
Re: C Construction Problem Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2018-02-20 11:11 -0700
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-20 18:30 +0000
Re: C Construction Problem Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-02-20 23:37 +0000
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-21 00:45 +0000
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-21 01:46 +0000
Re: C Construction Problem David Brown <david.brown@hesbynett.no> - 2018-02-21 08:49 +0100
Re: C Construction Problem Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-02-21 09:29 +0000
[OT] Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-21 11:24 +0000
Re: [OT] Re: C Construction Problem Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-02-21 14:41 +0300
Re: [OT] Re: C Construction Problem David Brown <david.brown@hesbynett.no> - 2018-02-21 15:10 +0100
Re: [OT] Re: C Construction Problem Robert Wessel <robertwessel2@yahoo.com> - 2018-02-21 12:36 -0600
Re: [OT] Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-21 21:04 +0000
Re: [OT] Re: C Construction Problem Robert Wessel <robertwessel2@yahoo.com> - 2018-02-21 18:20 -0600
Re: C Construction Problem Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-02-21 11:09 +0300
Re: C Construction Problem Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-02-21 02:29 -0800
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-21 11:32 +0000
Re: C Construction Problem Geoff <geoff@invalid.invalid> - 2018-02-26 11:02 -0800
Re: C Construction Problem David Brown <david.brown@hesbynett.no> - 2018-02-27 09:22 +0100
Re: C Construction Problem Geoff <geoff@invalid.invalid> - 2018-02-27 11:18 -0800
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-27 19:51 +0000
Re: C Construction Problem Robert Wessel <robertwessel2@yahoo.com> - 2018-02-28 01:54 -0600
Re: C Construction Problem Robert Wessel <robertwessel2@yahoo.com> - 2018-02-28 01:43 -0600
Re: C Construction Problem Geoff <geoff@invalid.invalid> - 2018-02-28 12:54 -0800
Re: archive decompressor Noob <root@127.0.0.1> - 2018-03-04 12:34 +0100
Re: C Construction Problem Anton Shepelev <anton.txt@g{oogle}mail.com> - 2018-02-21 11:04 +0300
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-21 11:27 +0000
Re: C Construction Problem Anton Shepelev <anton.txt@gmail.com> - 2018-02-28 22:59 +0300
Re: C Construction Problem supercat@casperkitty.com - 2018-02-21 08:49 -0800
Re: C Construction Problem Geoff <geoff@invalid.invalid> - 2018-02-26 11:08 -0800
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-26 23:51 +0000
Re: C Construction Problem Geoff <geoff@invalid.invalid> - 2018-02-27 11:24 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 08:07 -0800
Re: C Construction Problem fr314159@gmail.com - 2018-02-21 09:16 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 21:26 -0800
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-21 09:43 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-21 22:47 -0800
Re: C Construction Problem Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-02-22 13:09 +0000
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-24 13:37 -0800
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-22 10:50 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-24 13:58 -0800
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-24 15:05 -0800
Re: C Construction Problem Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-02-25 03:21 -0800
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-25 11:51 +0000
Re: C Construction Problem Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-02-25 04:06 -0800
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-25 12:47 +0000
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-25 13:20 +0000
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-25 17:46 +0000
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-25 18:58 +0000
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-25 20:01 +0000
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-25 20:25 +0000
Re: C Construction Problem Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-02-26 02:49 -0800
Re: C Construction Problem Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-02-25 20:02 +0000
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-25 15:13 -0800
Re: C Construction Problem Robert Wessel <robertwessel2@yahoo.com> - 2018-02-25 11:50 -0600
Re: C Construction Problem Ian Collins <ian-news@hotmail.com> - 2018-02-26 07:38 +1300
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-25 15:15 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-26 22:02 -0800
Re: C Construction Problem jameskuyper@verizon.net - 2018-02-27 06:32 -0800
Re: C Construction Problem GOTHIER Nathan <nathan.gothier@gmail.com> - 2018-02-27 16:56 +0100
Re: C Construction Problem jameskuyper@verizon.net - 2018-02-27 08:27 -0800
Re: C Construction Problem GOTHIER Nathan <nathan.gothier@gmail.com> - 2018-02-27 18:02 +0100
Re: C Construction Problem jameskuyper@verizon.net - 2018-02-27 10:23 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-03-03 01:09 -0800
Re: C Construction Problem David Brown <david.brown@hesbynett.no> - 2018-02-28 10:37 +0100
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-03-03 01:29 -0800
Re: C Construction Problem Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-03 02:00 -0800
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-27 08:46 -0800
Re: C Construction Problem jameskuyper@verizon.net - 2018-02-27 09:15 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-03-03 02:08 -0800
Re: C Construction Problem Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-03 02:31 -0800
Re: C Construction Problem Ian Collins <ian-news@hotmail.com> - 2018-03-04 10:34 +1300
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-03-19 10:27 -0700
Re: C Construction Problem jameskuyper@verizon.net - 2018-03-03 21:35 -0800
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-03-17 10:29 -0700
Re: C Construction Problem Steven Petruzzellis <frelwizzen@gmail.com> - 2018-03-18 08:14 -0700
Re: C Construction Problem David Brown <david.brown@hesbynett.no> - 2018-02-25 21:49 +0100
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-25 15:09 -0800
Re: C Construction Problem gazelle@shell.xmission.com (Kenny McCormack) - 2018-02-26 13:46 +0000
Re: C Construction Problem David Brown <david.brown@hesbynett.no> - 2018-02-26 14:57 +0100
Re: C Construction Problem Tim Rentsch <txr@alumni.caltech.edu> - 2018-02-26 22:14 -0800
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-22 00:11 +0000
Re: C Construction Problem Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2018-02-21 17:27 -0700
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-20 09:30 -0800
Re: C Construction Problem Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-02-21 00:23 +0000
Re: C Construction Problem Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2018-02-20 09:11 -0700
Re: C Construction Problem "F. Russell" <fr@random.info> - 2018-02-20 16:38 +0000
Re: C Construction Problem bartc <bc@freeuk.com> - 2018-02-20 17:07 +0000
Re: C Construction Problem John Bode <jfbode1029@gmail.com> - 2018-02-20 09:09 -0800
Re: C Construction Problem "James R. Kuyper" <jameskuyper@verizon.net> - 2018-02-20 12:18 -0500
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-20 09:38 -0800
Re: C Construction Problem Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2018-02-20 11:08 -0700
Re: C Construction Problem Gordon Burditt <gordon@hammy.burditt.org> - 2018-02-20 21:47 -0600
Re: C Construction Problem Keith Thompson <kst-u@mib.org> - 2018-02-21 09:36 -0800
Re: C Construction Problem Geoff <geoff@invalid.invalid> - 2018-02-26 11:21 -0800
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