hello,
1) First how following program get executed i mean how output is
printed and also why following program gives different output in Turbo
C++ compiler and Visual c++ 6 compiler?
void main()
{
int val=5;
printf("%d %d %d %d",val,--val,++val,val--);
}
under turbo compiler its giving
4 4 5 5
and under visual c++ its
5 5 6 5
2) How to evaluate following statement
int val =5;
val =- --val - val-- - --val;
Nov 15 '05
70  2815 
In article <is************ *************** *****@4ax.com>, Mark McIntyre
<ma**********@s pamcop.net> writes On 8 Jul 2005 03:11:03 -0700, in comp.lang.c , ra*******@gmail .com
wrote:
hello,
1) First how following program get executed i mean how output is
printed and also why following program gives different output in Turbo
C++ compiler and Visual c++ 6 compiler?
void main()
main must return an int - void main() is illegal C code.
Main only returns int in a hosted environment.
In free stranding environments there is nothing to return to. So
void main()
Is the only practical real world solution (and quite legal). The entry
point to the C program does not *have* to be called main but for the
majority of debugging tools it needs to be.
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
/\/\/ ch***@phaedsys. org www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
On Thu, 14 Jul 2005 14:35:19 +0100, in comp.lang.c , Chris Croughton
<ch***@keristor .net> wrote: On Thu, 14 Jul 2005 11:35:18 +0100, Mark McIntyre
<ma**********@s pamcop.net> wrote:
main must return an int - void main() is illegal C code.
It isn't 'illegal'
Illegal is CLC shorthand for "disallowed by the C standard" as I'm
sure you well know.
(the only place that word is used in the standard is
in the context of an "illegal instruction" raising a signal). It is
implementati on defined whether it is permitted in a hosted environment;
This is a very old topic of discussion. The C99 standard requires main
to return an int in a hosted environment. There's no implementation
defined-ness about it, and I believe its now widely agreed that the
final phrase of 5.1.2.2.1 (1) refers to the arguments of main.
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt >
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On Thu, 14 Jul 2005 18:20:44 +0100, in comp.lang.c , Chris Hills
<ch***@phaedsys .org> wrote: Main only returns int in a hosted environment.
In free stranding environments there is nothing to return to
Absolutely. Was the OP writing for a freestanding implementation?
I also note for reference that discussion of freestanding
implementations is generally regarded as offtopic here (or at least
largely pointless), since there are few requirements placed on such
implementations by the standard.
So
--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt >
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On Thu, 14 Jul 2005 14:23:00 +0000 (UTC), Walter Roberson
<ro******@ibd.n rc-cnrc.gc.ca> wrote: In article <sl************ ******@ccserver .keris.net>,
Chris Croughton <ch***@keristor .net> wrote:
:I do hope that no government makes certain C code illegal...
Cryptography, DVD decoders, viruses...
No, those are applications and can be written in any language. I'm
referring to C code itself, like making it a criminal offence to use
goto or break...
Chris C
On Thu, 14 Jul 2005 08:54:40 -0700, osmium
<r1********@com cast.net> wrote: "Chris Croughton" writes:
I do hope that no government makes certain C code illegal...
Good luck on your campaign to get programmers to speak English. You
should not expect quick results.
Indeed, even getting them to speak American would be hard <g>...
Chris C
On Thu, 14 Jul 2005 18:20:44 +0100, Chris Hills
<ch***@phaedsys .org> wrote: Main only returns int in a hosted environment.
In free stranding
Is that like lightweight threads? <g>
environments there is nothing to return to. So
void main()
Is the only practical real world solution (and quite legal). The entry
point to the C program does not *have* to be called main but for the
majority of debugging tools it needs to be.
I don't think I've come across an embedded debugging tool which cared
what the entry point is called, they seem to only need to know the start
address (if that isn't hardwired by the processor). Certainly the
mobile phone systems I've programmed at that level have had all sorts of
names for the entry point (boot, entry, startup, etc.) at a whim of the
original programmer or designer.
However, there are probably loads of debuggers I haven't used, every
processor manufacture seems to have their own favourites...
Chris C
In article <0c************ *************** *****@4ax.com>, Mark McIntyre
<ma**********@s pamcop.net> writes On Thu, 14 Jul 2005 18:20:44 +0100, in comp.lang.c , Chris Hills
<ch***@phaedsy s.org> wrote:
Main only returns int in a hosted environment.
In free stranding environments there is nothing to return to
Absolutely. Was the OP writing for a freestanding implementation?
I also note for reference that discussion of freestanding
implementation s is generally regarded as offtopic here (or at least
largely pointless), since there are few requirements placed on such
implementation s by the standard.
However there are probably as many free standing implementations as
hosted. Besides who is the authority to say half the C world is off
topic in a C language group.
However I take your point that in SOME areas the freestanding
implementation is unspecified or implementation defined
--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
/\/\/ ch***@phaedsys. org www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
Mark McIntyre <ma**********@s pamcop.net> wrote: This is a very old topic of discussion. The C99 standard requires main
^^^^^ to return an int in a hosted environment.
Would you please explain this to me, or give me some pointers
to past discussions where I could read about this myself?
I did google a bit, and found no proof of your assertion.
In fact, opinions on this (coming from the top clc gurus)
varied both ways.
There's no implementation
defined-ness about it, and I believe its now widely agreed that the
final phrase of 5.1.2.2.1 (1) refers to the arguments of main.
--
Stan Tobias
mailx `echo si***@FamOuS.Be dBuG.pAlS.INVALID | sed s/[[:upper:]]//g`
S.Tobias wrote: Mark McIntyre <ma**********@s pamcop.net> wrote:
This is a very old topic of discussion. The C99 standard requires main ^^^^^ to return an int in a hosted environment.
Would you please explain this to me,
Well, if you want your program to be portable, you have to return int.
Implementations are allowed to define behaviours for alternative return
types for main (they were in C90 too, but C99 merely makes this explicit),
so you can argue that void main is implementation-defined, but ONLY for
implementations that define it! In other implementations , it remains
undefined, and so it's not unreasonable to argue that the C99 standard
requires programs-intended-to-be-portable to return int.
or give me some pointers
to past discussions where I could read about this myself?
Pick 20 articles at random from comp.lang.c's archives. I should think that
at least 6 of them will be about void main.
I did google a bit, and found no proof of your assertion.
In fact, opinions on this (coming from the top clc gurus)
varied both ways.
The safe thing to do is go with int main, unless your implementation
actually forbids it (eg freestanding).
--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999 http://www.cpax.org.uk
mail: rjh at above domain ra*******@gmail .com wrote: hello,
1) First how following program get executed i mean how output is
printed and also why following program gives different output in Turbo
C++ compiler and Visual c++ 6 compiler?
void main()
{
int val=5;
printf("%d %d %d %d",val,--val,++val,val--);
}
under turbo compiler its giving
4 4 5 5
This is because turbo compiler executes such single line code from
right to left.
i.e., val-- gets first evaluated, next ++val and so on.
val -- prints a '5'(the value of variable val),substract value of 'val'
by 1, so that now val=4
Now ++val gets executed, ++ before val increments val before printing,
so you obtain a '5'.Now val=5
After this -- val gets executed, substracting 1 from val before
printing as said before and you get a '4' at the output.At this point
val=4
So finally val gets printed and you obtain the current value of the
'val' to be 4
It should be noted that though execution takes place from right to
left, printing takes place in the order defined in printf
It should also be noted that void main() is not a good practice, better
use int main() along with a return 0; just before you end the main()
and under visual c++ its
5 5 6 5
2) How to evaluate following statement
int val =5;
val =- --val - val-- - --val; This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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