Hi,
Whenever we type in this code
int main()
{
printf("%f",10) ;
}
we get an error. We can remove that by using #pragma directive t
direct that to the 8087. Even after that the output is 0.00000 and no
10.0000. Can anybody tell me why it is like that and why typecasting i
not done in this case?
-
andynai
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Nov 14 '05
63  3431 
Harti Brandt <br****@dlr.d e> writes: On Tue, 29 Jun 2004, Arthur J. O'Dwyer wrote:
[...] AJO> Who's been using "%d" or "%x" to print *pointer* values?
%p is a quite new feature for printf(). Neither V7 nor BSD had this, so
the natural way of printing pointers was %x. Don't assume that everybody
out there does a daily update of it's compilers and libraries to the
current gcc.
It's not *that* new; it was introduced in the 1989 ANSI C standard, at
the same time prototypes were introduced. It did take several years
for ANSI C to catch on widely enough for "%p" to be considered
portable, but certainly any code written in the last decade or so
should use it.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
jacob navia <ja***@jacob.re mcomp.fr> wrote: I think lcc-win32 will eventually migrate to
sizeof(void *) == 32, sizeof(int) 32
sizeof( __long void *) == 64, sizeof (long long) == 64.
For the few data items where you may need more than
4GB of addressing space a special pointer type would be more efficient
Do we have to expect the return of the dreaded far and near pointer
issues in a new disguise? Please tell me you don't even consider
something like that....
Regards, Jens
--
\ Jens Thoms Toerring ___ Je***********@p hysik.fu-berlin.de
\______________ ____________ http://www.toerring.de
<Je***********@ physik.fu-berlin.de> a écrit dans le message de
news:2k******** ***@uni-berlin.de... jacob navia <ja***@jacob.re mcomp.fr> wrote: I think lcc-win32 will eventually migrate to
sizeof(void *) == 32, sizeof(int) 32
sizeof( __long void *) == 64, sizeof (long long) == 64.
For the few data items where you may need more than
4GB of addressing space a special pointer type would be more efficient
Do we have to expect the return of the dreaded far and near pointer
issues in a new disguise? Please tell me you don't even consider
something like that....
Well, if you do not want that, you should use all 64 bit
pointers. I will allow a switch for that since anyway I have
implemented a 64 bit only mode first.
A 32 bit mode with all pointers 32 bit by default is
more efficient in space and also in time for many applications.
This will not work very well if the added complexity doesn't justify
the performance gains. But for *many* existing and many
complex programs, a 64 bit pointer is an overkill and 32 bits
will suffice wonderfully. Not all software is handling big
database applications. Why carry all those zeroes around?
jacob navia wrote: The expression
printf("the address is: 0x%x\n",p);
where p is some pointer appears in several million lines in
existing code.
...
This simply means that authors of such code are in desperate need of
additional education in C programming (even though they might not
realize that). In this particular case the problem with the code is not
hypothetical, it is very real. Just consider what will happen on 64-bit
platform with 32-bit ints.
--
Best regards,
Andrey Tarasevich
"jacob navia" <ja***@jacob.re mcomp.fr> writes: "Keith Thompson" <ks***@mib.or g> a écrit dans le message de
news:ln******** ****@nuthaus.mi b.org...
[...] Then there are several million errors, and you'd be doing your users a
favor by letting them know.
If they set the debug level to high then yes. If not, the compiler
accepts it. I think this discussion has shown me that
maybe a warning is needed, if the programmer wishes.
In my opinion, the warning is needed whether the programmer asks for
it or not.
lcc-win32 (as its name implies) is a 32 bit system. I am working
in the 64 bit version already, but that is another topic.
The name also implies that it's a C compiler. In C, calling printf()
with a "%d" or "%x" format and a pointer argument invokes undefined
behavior.
[...]
Yes. I started porting the code and it is hard. Warnings like this
could improve the situation. In any case in the 64 bit system a warning
will be issued since sizeof(int) != sizeof(void *).
A call like
printf("p = 0x%x\n", some_pointer_va lue);
isn't correct on a 32-bit system and incorrect on a 64-bit system.
It's incorrect in C, regardless of the particular implementation; it
just happens to "work" on some 32-bit systems (or more generally, on
some, but not all, systems where ints and pointers happen to be the
same size).
[...] The result may or may not be meaningful,
but at least it avoids undefined behavior.
Or you can just use "%p", which exists for exactly this purpose.
Yes, I think I will be forced to write that in the 64 bit system.
Why wait?
I am wary of forcing casts to please the compiler... In a 32
bit system where sizeof void * is the same as sizeof int, this
warning has no sense really, and should be optional.
Your wariness about casts is appropriate. Arguments to printf() are
among the rare cases where they're necessary (the prototype doesn't
force an implicit conversion, so you need an explicit one). Even
passing a pointer argument for a "%p" format calls for a cast to void*
(though it's probably not strictly necessary for char*).
Do not clutter output. Filter it. Make more verbose
options available but choose a sensible default:
do not clutter...
A warning about incorrect code is not clutter.
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
In article <cb**********@n ews-reader5.wanadoo .fr>,
"jacob navia" <ja***@jacob.re mcomp.fr> wrote: "Christian Bau" <ch***********@ cbau.freeserve. co.uk> a écrit dans le message
de news:ch******** *************** **********@slb-newsm1.svr.pol. co.uk... In article <cb**********@n ews-reader5.wanadoo .fr>,
"jacob navia" <ja***@jacob.re mcomp.fr> wrote:
I think lcc-win32 will eventually migrate to
sizeof(void *) == 32, sizeof(int) 32
sizeof( __long void *) == 64, sizeof (long long) == 64.
Are you sure about that?
The rationale is that most programs do have a certain use of the
extra registers provided by the new architecture, but will never
need more than 4GB address range for most pointers.
So why would you need sizeof (void *) == 32? Don't you think that 256
bit pointers are a bit excessive and 256 bit int is a bit much as well?
On Wed, 30 Jun 2004, jacob navia wrote:
<Je***********@ physik.fu-berlin.de> a écrit... jacob navia <ja***@jacob.re mcomp.fr> wrote: I think lcc-win32 will eventually migrate to
sizeof(void *) == 32, sizeof(int) 32
sizeof( __long void *) == 64, sizeof (long long) == 64.
Do we have to expect the return of the dreaded far and near pointer
issues in a new disguise? Please tell me you don't even consider
something like that....
Well, if you do not want that, you should use all 64 bit
pointers. I will allow a switch for that since anyway I have
implemented a 64 bit only mode first.
A 32 bit mode with all pointers 32 bit by default is
more efficient in space and also in time for many applications.
This will not work very well if the added complexity doesn't justify
the performance gains. But for *many* existing and many
complex programs, a 64 bit pointer is an overkill and 32 bits
will suffice wonderfully. Not all software is handling big
database applications. Why carry all those zeroes around?
I second Jens' comment. Have you had any experience with the
'far'/'near' morass? It's exactly isomorphic to your '__long'
proposal, except that 'far' and 'near' were dinosaurs of the
16-to-32-bit transition, and your proposal is a dinosaur of the
32-to-64-bit transition. It ought never to see the light of day.
(On the other hand, I don't think there's much real danger that
anyone will use lcc-win32 as their primary source-developing
platform, in the same way Borland[1] dominated many areas during the
last ice age. And I do have a perverse fascination with archaic
hacks like 'far'/'near'. So maybe I would prefer to see Jacob
struggle this one out... ;)
The "correct" solution, as far as I'm concerned, is to go ahead
and use 32-bit pointers whenever possible --- but *hide this fact
from the user*! That is, have only a single type 'void*', but let
it be 32 bits most of the time and 64 bits when necessary. If
it's too hard to figure out when 32 bits are truly sufficient, then
go the "memory model" route (which you already suggested as an
alternative). But steer clear of 'far' and 'near'!
-Arthur
[1] - It *was* "Turbo <PLOC>" that introduced 'far' and 'near',
wasn't it, and then Microsoft picked it up? Or was it invented
several times independently?
On Wed, 30 Jun 2004, Keith Thompson wrote:
"jacob navia" <ja***@jacob.re mcomp.fr> writes:
[re: warning about 'printf("%d", cptr)'] If they set the debug level to high then yes. If not, the compiler
accepts it. I think this discussion has shown me that
maybe a warning is needed, if the programmer wishes.
In my opinion, the warning is needed whether the programmer asks for
it or not.
Especially for a reason Dan Pop pointed out twice, which seems to
have been ignored in all the 64-bit "clutter";) ...
char *p = "foo";
if (should_we_prin t_foo)
printf("%d\n", p);
Whoops! The programmer meant to type "%s", but his finger slipped
from the 's' to the adjacent 'd' key, and his program will have a
subtle bug. Not so subtle if "foo" is an important prompt, but
suppose "foo" is an error message that only appears during weekly
progress meetings? ;)
"Oh, that's no problem... I'll fix the typo and recompile," says
the programmer.
char *p = "foo";
if (should_we_prin t_foo)
printf("%x\n", p);
Whoops! Dang that 's' key --- this time I hit 'x' by mistake instead!
And again lcc-win32 conspires to hide my mistake.
This is a system of compiler diagnostics truly worthy of the DS9000,
if it will hide *only* those 'printf' errors which could conceivably
be typing mistakes! (I bet it warns about printf("%d") on a float,
or vice versa, though, so it's not yet perfect. ;)
-Arthur
"jacob navia" <ja***@jacob.re mcomp.fr> writes:
[...] I think lcc-win32 will eventually migrate to
sizeof(void *) == 32, sizeof(int) 32
sizeof( __long void *) == 64, sizeof (long long) == 64.
Assuming that by sizeof(foo) you mean sizeof(foo)*CHA R_BIT ...
So you're not planning to allow code compiled by lcc-win32
(lcc-win64?) to interface easily to code compiled by other compilers?
Like, say, the operating system?
--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
"jacob navia" <ja***@jacob.re mcomp.fr> wrote: In any case this discussion was positive for me (and lcc-win32).
I have been able to improve lcc-win32 a bit.
I hope you have the decency to credit comp.lang.c in your documentation
for any correct parts of that compiler.
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