printf and cout

[Richard Heathfield]

Re: printf and cout

Bernhard Schauer said:

>><snip>
>>>Actually they don't behave differently at all. In each case the int
>>>value 400 is being interpreted as an unsigned char.
>><snip>
>>>
>>Code from laikon:
>>>int c = 400;
>>>printf("%c ", c);
>>>cout << int(char(400));
>>>
>>Where exactly do you see unsigned characters? (char != unsigned char)

>>
>The %c format expects (and thus treats the corresponding argument as) an
>unsigned char.

>
Ok. But I hope char(400) does not convert to an unsigned char?

Actually, char(400) converts to a syntax error.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Chris Dollin]

Re: printf and cout

Richard Heathfield wrote:

Bernhard Schauer said:
>

>>><snip>
>>>>Actually they don't behave differently at all. In each case the int
>>>>value 400 is being interpreted as an unsigned char.
>>><snip>
>>>>
>>>Code from laikon:
>>>>int c = 400;
>>>>printf("%c" , c);
>>>>cout << int(char(400));
>>>>
>>>Where exactly do you see unsigned characters? (char != unsigned char)
>>>
>>The %c format expects (and thus treats the corresponding argument as) an
>>unsigned char.

>>
>Ok. But I hope char(400) does not convert to an unsigned char?

>
Actually, char(400) converts to a syntax error.

But the code it appears in is, atopically, C++, and so how it behaves
in C doesn't much matter ...

The C equivalentish code, `(char) 400`, doesn't convert to unsigned
char, but to char -- which may be an unsigned type, or not, at the
implementor's whim, perhaps with an eye on performance implications
(and mobs with torches and pitchforks).

--
"What would that matter, if it made a good book?" /Gaudy Night/

Hewlett-Packard Limited registered office: Cain Road, Bracknell,
registered no: 690597 England Berks RG12 1HN

[Bernhard Schauer]

Re: printf and cout

Richard Heathfield wrote:

Actually, char(400) converts to a syntax error.

Sorry. Mixed up C/C++ (again). Meant (char)400 as Chris pointed out.

--
Bernhard Schauer
schauer_at_crux y_dot_net

[Mark McIntyre]

Re: printf and cout

Richard Heathfield wrote:

laikon said:
>

>Hello, everyone:
>>
>this is about overflow in C and C++.

>
The behaviour of a C program on overflow is undefined.
>

>int c = 400;
>printf("%c", c);
>>
>it print ? on screen,

>
Not necessarily. C doesn't guarantee you a screen, and it says very little
about the character set supplied by your implementation.
>

>and ascii of '?' is 63.

>
This is irrelevant, I think. If by some chance you'd seen the character
with code point 144 (which is, of course, *not* an ASCII character), I'd
have been able to explain it in concrete terms. I am a little puzzled by
the 63, actually.

Its not printing 63, its just printing "?" to mean "I don't know how to
represent a value outside the characterset this screen uses".

[pete]

Re: printf and cout

santosh wrote:

The %c format expects
(and thus treats the corresponding argument as) an unsigned char.

No standard library functions are described
as taking an argument lower ranking than int.

--
pete

[Kenneth Brody]

Re: printf and cout

Richard Heathfield wrote:

>
jacob navia said:

[...]

That's what I am talking about. Obviously your example
will work.

printf("%c",123 45678);

will not!

>
It is certainly true that it is not guaranteed to work. It is not
guaranteed *not* to work, however. On systems with CHAR_BIT >= 24, it
/will/ work (although heaven knows what character will be printed!).

Well, it depends on what you mean by "work". According to 7.19.6.1p8,
on the part about the "%c" format:

If no l length modifier is present, the int argument is converted
to an unsigned char, and the resulting character is written.

Is it possible to "fail" when converting an int to unsigned char? (Of
course you can lose bits, but can it "fail"?)

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer .h|
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:ThisIsA SpamTrap@gmail. com>

[Keith Thompson]

Re: printf and cout

jacob navia <jacob@nospam.c omwrites:
[...]

Well OK
>
"%c" format specifier expects an int.

Correct.

GREAT!
>
I am tired of this discussion.

Funny that you happen to get "tired" of it just at the moment when you
realize you made a mistake.

You are right, I was wrong

Yes, I was right. Yes, you were wrong. But it's not such a
huge deal. We all make mistakes. I make mistakes all the time,
and I'm grateful when people point them out. And I usually accept
corrections without sarcasm.

and when everybody uses "%c" to put a character they are
totally wrong.

And now you're being ridiculous. This:

char c = 'x';
printf("%c", c);

is perfectly valid, because the char value is promoted to int,
which is what printf expects for "%c". (Except in the obscure
case that plain char is unsigned and sizeof(int) == 1, but I'm
willing to ignore that (other than this brief mention for the sake
of completeness).) But of course you know that.

Pointing out an error is not a personal attack. Learn that and
you might be taken a lot more seriously around here.

--
Keith Thompson (The_Other_Keit h) <kst-u@mib.org>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[pete]

Re: printf and cout

Keith Thompson wrote:

>
jacob navia <jacob@nospam.c omwrites:
[...]

Well OK

"%c" format specifier expects an int.

>
Correct.
>

GREAT!

I am tired of this discussion.

>
Funny that you happen to get "tired" of it just at the moment when you
realize you made a mistake.
>

You are right, I was wrong

>
Yes, I was right. Yes, you were wrong. But it's not such a
huge deal. We all make mistakes. I make mistakes all the time,
and I'm grateful when people point them out. And I usually accept
corrections without sarcasm.
>

and when everybody uses "%c" to put a character they are
totally wrong.

>
And now you're being ridiculous. This:
>
char c = 'x';
printf("%c", c);
>
is perfectly valid, because the char value is promoted to int,
which is what printf expects for "%c". (Except in the obscure
case that plain char is unsigned and sizeof(int) == 1, but I'm
willing to ignore that (other than this brief mention for the sake
of completeness).) But of course you know that.
>
Pointing out an error is not a personal attack. Learn that and
you might be taken a lot more seriously around here.

This will output the same thing
even though the int argument is negative:

printf("%c", 'x' - 1 - (unsigned char)-1);

except in that obscure case that you mentioned.

--
pete

[pete]

[ot]Re: printf and cout

Philip Potter wrote:

I especially can't understand it when
the correction comes from someone as calm and civil as Keith.

I can almost understand.

One of the things that I admire about Richard Heathfield
is his ability to make trolls come unglued.
Troll that are not bothered by anyone else.
Mostly I've seen this happen in comp.programmin g.
He does it "calm and civil"
with politeness and with with a finess
that is very difficult to describe or duplicate.

--
pete

[Richard Heathfield]

Re: [ot]Re: printf and cout

pete said:

Philip Potter wrote:
>

>I especially can't understand it when
>the correction comes from someone as calm and civil as Keith.

>
I can almost understand.
>
One of the things that I admire about Richard Heathfield
is his ability to make trolls come unglued.
Troll that are not bothered by anyone else.
Mostly I've seen this happen in comp.programmin g.
He does it "calm and civil"
with politeness and with with a finess
that is very difficult to describe or duplicate.

I wish I could claim that it's deliberate (because then I could simply stop
doing it) - a sort of "meta-trolling", or trolling the trolls, pushing
their buttons to make them react in their oh-so-predictable way.

But it isn't deliberate. The trigger would appear to be some facet or other
of my writing style, which many non-trolls do seem to find helpful and
clear, but which appears to drive the trolls to distraction.

When the trolls start providing useful articles about C here (i.e. when
hell freezes over, or perhaps a few months afterwards), I'll give some
thought to discovering ways in which I might change my style to avoid
"ungluing" them, as you so aptly put it. In the meantime, I'll continue
providing such help as I can to those who seek it in the way that seems
best to me, and if that means that a few bozos continue to clog up the
newsgroup with puerile nonsense, well, that's what killfiles are for,
right?

Some people don't killfile the trolls, because they find them amusing.
Obviously that's up to them. Nevertheless, I would invite such people to
consider the (fairly simple) challenge of writing a C program to mimic an
article by any of the current collection of comp.lang.c trolls. A few
stock phrases will be sufficient, I think. Slightly more challenging (but
really not *very* much more): generate random but characteristic troll
*exchanges*. You know the sort of thing:

T1: Oh. The. Irony.
T2: Yes, you're right.
T1: Too true.
T3: You're both so right.

etc.

To implement such a program in ISO C should take - oh, ten minutes, tops.

Once you've written such a program and run it a few times, you'll soon have
the shape of the solution space mapped out, after which it really ceases
to be particularly funny - at which point you may well decide to use a
killfile after all.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Richard]

Re: [ot]Re: printf and cout

pete <pfiland@mindsp ring.comwrites:

Philip Potter wrote:
>

>I especially can't understand it when
>the correction comes from someone as calm and civil as Keith.

>
I can almost understand.
>
One of the things that I admire about Richard Heathfield
is his ability to make trolls come unglued.
Troll that are not bothered by anyone else.
Mostly I've seen this happen in comp.programmin g.
He does it "calm and civil"
with politeness and with with a finess
that is very difficult to describe or duplicate.

RH's skills in terms of C are without question. However he is pedantic
to the point of silliness. And that combined with his rather nasty
tendency to pick at people and wage warfare on one or two alternative,
but equally valuable, posters make him an object for ridicule rather
than admiration for most professional programmers who are used to
dealing with this type of technical ogre.

[pete]

Re: [ot]Re: printf and cout

Richard wrote:

>
pete <pfiland@mindsp ring.comwrites:

One of the things that I admire about Richard Heathfield
is his ability to make trolls come unglued.

RH's skills in terms of C are without question.

And on top of that,
he's one of the only seven posters to this newsgroup
who use the phrase "begging the question" correctly.

--
pete

[Philip Potter]

Re: [ot]Re: printf and cout

pete wrote:

Richard wrote:

>pete <pfiland@mindsp ring.comwrites:

>

>>One of the things that I admire about Richard Heathfield
>>is his ability to make trolls come unglued.

>

>RH's skills in terms of C are without question.

>
And on top of that,
he's one of the only seven posters to this newsgroup
who use the phrase "begging the question" correctly.
>

Which begs the question: who are the others? ;)

Phil

[David Thompson]

Re: printf and cout

On Fri, 28 Mar 2008 07:08:48 -0500, pete <pfiland@mindsp ring.com>
wrote:

santosh wrote:
>

The %c format expects
(and thus treats the corresponding argument as) an unsigned char.

>
No standard library functions are described
as taking an argument lower ranking than int.

Some take implementation-defined types which _could_ be lower.

size_t: *alloc, qsort/bsearch, fread/write, *snprintf/*swprintf,
several mem*/str*/wcs*, etc.

time_t: difftime

(va_list could be smaller than int, but all va_* are not actual
functions; jmp_buf must be an array type)

- formerly david.thompson1 || achar(64) || worldnet.att.ne t