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Groups > comp.lang.c > #147561
| Subject | Re: memcpy not memcpying? |
|---|---|
| Newsgroups | comp.lang.c |
| References | (14 earlier) <lnv9s169ev.fsf@kst-u.example.com> <1BAvF.13970$mB7.12243@fx32.am4> <qpn0a2$dn3$1@dont-email.me> <%%DvF.115593$Yl3.480@fx24.am4> <qpnj12$17q$1@dont-email.me> |
| From | Bart <bc@freeuk.com> |
| Message-ID | <BoJvF.123253$m0L.2016@fx15.am4> (permalink) |
| Organization | virginmedia.com |
| Date | 2019-11-03 23:28 +0000 |
On 03/11/2019 22:06, David Brown wrote:
> On 03/11/2019 18:20, Bart wrote:
>> (1) A numeric type T exported from a library's header. You want to print
>> it, but now you have to delve into the header to find out what type
>> it is, to work out what format it needs.
>>
>
> I don't use types when I don't know their relevant characteristics.
You do some includes such as:
#include <windows.h>
#include <gtk.h>
and you're importing possibly 1000s of types. You're not going to be
able to keep track of them. And every so often, you will need to
printout values of those types, or the results of calculations with
those types.
> Have you ever heard the phrase "Don't repeat yourself", with the acronym
> DRY? You write code to output the type once, and use it wherever it is
> needed. If T changes, you change the one function.
Huh? You write this
int nsymbols;
In 100 places in the program, you might have code like this:
printf("Symbol %d out of %d",i, nsymbols);
Then one day, you decide to change it to:
long long int nsymbols;
Now all those %d's that refer to nsymbols in a format string need to be
changed. Plus possibly variables such as that 'i' above, and /its/ format.
If nsymbols is defined in some imported header, you might not even be
aware of any change.
> Of course, that kind of coding might be unfamiliar to someone who
> rejects majors, inline functions, typedefs, and other features aimed at
> such abstractions in coding.
Yet the entire C language rejects type abstraction when it comes to
printf formats!
> #if cond
> int x;
> #define PRIx %d
> #elif
> double x;
> #define PRIx %f
> #endif
Yuck.
However nobody actually does it. (Look at one of those 50-line #if/#elif
chains of conditionals that end up defining some vital type. They NEVER
also define a corresponding print format.)
And this definition could be inside someone else's header that you are
importing.
All you want to do is quickly print the value of .st_rdev of a 'stat'
struct, of which one of half a dozen variations could be conditionally
defined. Good luck finding a print format defined too! It's just not
going to happen.
Your best bet might be actually printing as float, and converting to
float, provided the magnitude is under 2**52, but it's a hell of thing
to have to do, especially if you'd prefer it as hex!
printf("s.st_rdev = %f\n", (double)s.st_rdev);
compared with:
printf("%=?\n", s.strdev);
> As I say, I don't write code using types that I don't know. So your
> complaint is meaningless.
No it isn't. It's perfectly legitimate. You're debugging someone's
100,000-line project with a thousand types, and thousands of variables
and functions of different types, and you need to print out the value of
the index here:
a[f(x)+y]=0;
as printf("f(x)+y = %...\n", f(x)+y); but what goes in the "..."? You
have to assume it is something compatible with int or size_t (you don't
even know what type array indices are supposed to be!), but you can't
tell just from that fragment.
All your suggestions are workarounds and mitigations for a fundamental
short-coming.
>>
>> The "%?" suggestion works with all of these when the type is numeric,
>> and in many cases also when the type is a pointer or string.
>
> It is an idea that can work in a more interpreted style of language. It
> is not a bad idea, and could be very convenient.
It is. I can write for my above example:
printf("f(x)+y= %?\n",f(x)+y);
and not know nor care what the relevant types are. I've just tried it
and it works with int, long long int, double or even char*. It's less
work, more productive and less error prone.
> If "%?" is something that works for you in your languages, great. That
> does not mean it is something that other people would like in C.
I think they would. Ben said in another post that Haskell has C-like
formats, but also "v" that works for any variable. That is the
equivalent of my "?" (which I can change to "v" if that has no existing
meaning).
But I can't imagine when someone writing Haskell would want to bother
with anything other than "v".
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memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-01 08:42 -0400
Re: memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-01 08:49 -0400
Re: memcpy not memcpying? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-01 09:24 -0400
Re: memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-01 09:46 -0400
Re: memcpy not memcpying? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-01 09:49 -0400
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-01 10:19 -0700
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-01 21:14 +0100
Re: memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-01 17:16 -0400
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-01 22:42 +0000
Re: memcpy not memcpying? Richard Damon <Richard@Damon-Family.org> - 2019-11-01 21:10 -0400
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-02 11:36 +0000
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-02 02:15 -0700
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-02 13:04 +0100
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-02 13:43 +0000
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-02 17:24 +0100
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-02 17:00 +0000
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-02 13:06 -0700
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-02 21:05 +0000
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-02 22:40 +0000
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-02 15:59 -0700
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-02 23:47 +0000
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-02 18:22 -0700
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 13:27 +0000
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-03 17:46 +0100
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 17:20 +0000
Re: memcpy not memcpying? Manfred <noname@add.invalid> - 2019-11-03 19:44 +0100
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 19:36 +0000
Re: memcpy not memcpying? Manfred <noname@add.invalid> - 2019-11-03 22:57 +0100
Re: memcpy not memcpying? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-03 22:39 +0000
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-03 23:06 +0100
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 23:28 +0000
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-04 11:00 +0100
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-04 11:14 +0000
Re: memcpy not memcpying? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-04 11:22 +0000
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-04 13:10 +0100
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-04 10:03 -0800
Re: memcpy not memcpying? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-04 19:36 +0000
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-05 10:04 -0800
Re: memcpy not memcpying? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-04 20:58 -0800
Re: memcpy not memcpying? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-04 22:01 -0800
Re: memcpy not memcpying? Autist <autist69@gmail.com> - 2019-11-04 12:56 +0100
Re: memcpy not memcpying? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-04 09:50 -0500
Re: memcpy not memcpying? scott@slp53.sl.home (Scott Lurndal) - 2019-11-04 20:26 +0000
Re: memcpy not memcpying? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-11-04 04:34 -0800
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-04 13:05 +0000
Re: memcpy not memcpying? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-04 14:09 +0000
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-04 15:11 +0000
Re: memcpy not memcpying? Melzzzzz <Melzzzzz@zzzzz.com> - 2019-11-04 15:15 +0000
Re: memcpy not memcpying? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-04 15:43 +0000
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 20:20 +0000
Re: memcpy not memcpying? Ian Collins <ian-news@hotmail.com> - 2019-11-03 14:37 +1300
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 11:01 +0000
Re: memcpy not memcpying? Öö Tiib <ootiib@hot.ee> - 2019-11-03 04:03 -0800
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 12:52 +0000
Re: memcpy not memcpying? Öö Tiib <ootiib@hot.ee> - 2019-11-03 23:34 -0800
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-04 09:36 +0000
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-04 16:20 +0000
Re: memcpy not memcpying? Ian Collins <ian-news@hotmail.com> - 2019-11-04 07:46 +1300
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-03 12:26 -0800
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-03 17:31 +0100
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-03 17:05 +0000
Re: memcpy not memcpying? already5chosen@yahoo.com - 2019-11-03 09:14 -0800
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-03 12:32 -0800
Re: memcpy not memcpying? already5chosen@yahoo.com - 2019-11-03 14:59 -0800
Re: memcpy not memcpying? already5chosen@yahoo.com - 2019-11-03 15:19 -0800
Re: memcpy not memcpying? already5chosen@yahoo.com - 2019-11-03 17:00 -0800
Re: memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-02 11:16 -0400
Re: memcpy not memcpying? David Brown <david.brown@hesbynett.no> - 2019-11-02 17:26 +0100
Re: memcpy not memcpying? Barry Schwarz <schwarzb@delq.com> - 2019-11-01 06:39 -0700
Re: memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-01 09:56 -0400
Re: memcpy not memcpying? Barry Schwarz <schwarzb@delq.com> - 2019-11-01 12:39 -0700
Re: memcpy not memcpying? guinness.tony@gmail.com - 2019-11-01 06:49 -0700
Re: memcpy not memcpying? jak <nospam@please.ty> - 2019-11-01 20:40 +0100
Re: memcpy not memcpying? Autist <autist69@gmail.com> - 2019-11-01 14:26 +0100
Re: memcpy not memcpying? Keith Thompson <kst-u@mib.org> - 2019-11-01 10:22 -0700
Re: memcpy not memcpying? Bart <bc@freeuk.com> - 2019-11-01 19:44 +0000
Re: memcpy not memcpying? Autist <autist69@gmail.com> - 2019-11-01 21:31 +0100
Re: memcpy not memcpying? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-01 09:39 -0400
Re: memcpy not memcpying? Autist <autist69@gmail.com> - 2019-11-01 14:42 +0100
Re: memcpy not memcpying? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-01 09:48 -0400
Re: memcpy not memcpying? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-11-01 06:47 -0700
Re: memcpy not memcpying? Autist <autist69@gmail.com> - 2019-11-01 14:58 +0100
Re: memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-01 10:22 -0400
Re: memcpy not memcpying? Autist <autist69@gmail.com> - 2019-11-01 18:38 +0100
Re: memcpy not memcpying? scott@slp53.sl.home (Scott Lurndal) - 2019-11-01 17:54 +0000
Re: memcpy not memcpying? Autist <autist69@gmail.com> - 2019-11-01 20:24 +0100
Re: memcpy not memcpying? DFS <nospam@dfs.com> - 2019-11-01 15:24 -0400
Re: memcpy not memcpying? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-01 23:19 +0000
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