strtol library function

[David Scarlett]

Another two questions...

Is behaviour defined when the first argument of strtol is NULL?

And if the string contains only digits, is the 2nd argument (assuming
it wasn't NULL) guaranteed to be set to a pointer to a pointer to '\0'?


Thanks.

--
David Scarlett

dscarlett@_ _ _ _ _ _ _ _
_ _ _ _ _ optusnet.com.au

[P.J. Plauger]

Re: strtol library function

"David Scarlett" <look@my.signat ure> wrote in message
news:Xns94EAC87 161287dscarlett @211.29.133.50. ..
[color=blue]
> Another two questions...
>
> Is behaviour defined when the first argument of strtol is NULL?[/color]

No.
[color=blue]
> And if the string contains only digits, is the 2nd argument (assuming
> it wasn't NULL) guaranteed to be set to a pointer to a pointer to '\0'?[/color]

The second argument is passed by value as a pointer to pointer. It makes
no sense to talke about what it might get set to. But the pointer it
points at on a successful return should designate the terminating NUL,
in the case you describe. I think that's what you really meant.

P.J. Plauger
Dinkumware, Ltd.

http://www.dinkumware.com

[Al Bowers]

Re: strtol library function



David Scarlett wrote:[color=blue]
> Another two questions...
>
> Is behaviour defined when the first argument of strtol is NULL?
>[/color]

The first agrument must be a value that represents a pointer to
a string. A value of NULL is not defined for the function.

I have a question regarding errno. Given the following code, which
simply detects if there was a proper coversion or not, is the test
using LONG_MIN or LONG_MAX neccessary or can one use use the test
errno == ERANGE?

#include <stdio.h>
#include <limits.h>
#include <errno.h>
#include <stdlib.h>

int main(void)
{
char *str = "-123456789999999 999999", *s;
long num = 0;

errno = 0;
num = strtol(str,&s,1 0);
if(s == str || *s != '\0' ||
((errno == ERANGE) && (num == LONG_MAX || num == LONG_MIN)))
printf("\"%s\" does not convert to a long value\n",str);
else
printf("\"%s\" = %ld\n",str,num) ;
return 0;
}


--
Al Bowers
Tampa, Fl USA
mailto: xabowers@myrapi dsys.com (remove the x to send email)

http://www.geocities.com/abowers822/

[P.J. Plauger]

Re: strtol library function

"Al Bowers" <xabowers@rapid sys.com> wrote in message
news:2gmoafF4kc 7aU1@uni-berlin.de...
[color=blue]
> I have a question regarding errno. Given the following code, which
> simply detects if there was a proper coversion or not, is the test
> using LONG_MIN or LONG_MAX neccessary or can one use use the test
> errno == ERANGE?
>
> #include <stdio.h>
> #include <limits.h>
> #include <errno.h>
> #include <stdlib.h>
>
> int main(void)
> {
> char *str = "-123456789999999 999999", *s;
> long num = 0;
>
> errno = 0;
> num = strtol(str,&s,1 0);
> if(s == str || *s != '\0' ||
> ((errno == ERANGE) && (num == LONG_MAX || num == LONG_MIN)))
> printf("\"%s\" does not convert to a long value\n",str);
> else
> printf("\"%s\" = %ld\n",str,num) ;
> return 0;
> }[/color]

The test of errno should suffice.

P.J. Plauger
Dinkumware, Ltd.

http://www.dinkumware.com

[Al Bowers]

Re: strtol library function



P.J. Plauger wrote:[color=blue]
> "Al Bowers" <xabowers@rapid sys.com> wrote in message
> news:2gmoafF4kc 7aU1@uni-berlin.de...
>
>[color=green]
>>I have a question regarding errno. Given the following code, which
>>simply detects if there was a proper coversion or not, is the test
>>using LONG_MIN or LONG_MAX neccessary or can one use use the test
>>errno == ERANGE?
>>
>>#include <stdio.h>
>>#include <limits.h>
>>#include <errno.h>
>>#include <stdlib.h>
>>
>>int main(void)
>>{
>> char *str = "-123456789999999 999999", *s;
>> long num = 0;
>>
>> errno = 0;
>> num = strtol(str,&s,1 0);
>> if(s == str || *s != '\0' ||
>> ((errno == ERANGE) && (num == LONG_MAX || num == LONG_MIN)))
>> printf("\"%s\" does not convert to a long value\n",str);
>> else
>> printf("\"%s\" = %ld\n",str,num) ;
>> return 0;
>>}[/color]
>
>
> The test of errno should suffice.
>[/color]

Yeah! That is the way I always used it. But recently someone mentioned
that there is nothing to prevent the a function implementation from
setting errno to ERANGE even if the resulting value is in the range
of a long. I looked at the Standard's description of the function and
saw that it id say the an unrepresentable value would result in both
errno == ERANGE and the return value either LONG_MAX or LONG_MIN.

--
Al Bowers
Tampa, Fl USA
mailto: xabowers@myrapi dsys.com (remove the x to send email)

http://www.geocities.com/abowers822/

[Emmanuel Delahaye]

Re: strtol library function

In 'comp.lang.c', David Scarlett <look@my.signat ure> wrote:
[color=blue]
> Is behaviour defined when the first argument of strtol is NULL?[/color]

No.
[color=blue]
> And if the string contains only digits, is the 2nd argument (assuming
> it wasn't NULL) guaranteed to be set to a pointer to a pointer to '\0'?[/color]

The argument is unchanged. It's the pointed value that is changed to a
pointer to '\0'.

--
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The C-language FAQ: http://www.eskimo.com/~scs/C-faq/top.html
C-reference: http://www.dinkumware.com/manuals/reader.aspx?lib=c99
FAQ de f.c.l.c : http://www.isty-info.uvsq.fr/~rumeau/fclc/

[Paul Emmons]

Re: strtol library function

On Sat, 15 May 2004 12:51:16 -0400, Al Bowers <xabowers@rapid sys.com>
wrote:
[color=blue]
>Yeah! That is the way I always used it. But recently someone mentioned
>that there is nothing to prevent the a function implementation from
>setting errno to ERANGE even if the resulting value is in the range
>of a long. I looked at the Standard's description of the function and
>saw that it id say the an unrepresentable value would result in both
>errno == ERANGE and the return value either LONG_MAX or LONG_MIN.[/color]

Perhaps that was in the course of my stupid question about strtoul(),
which I erroneously claimed that it returned ERANGE for input between
LONG_MAX and ULONG_MAX. It doesn't. I was actually playing with
strtol() instead, and didn't realize it.

It still seems rather strange to me that strtoul() accepts "-2" and
returns 4294967294 without complaint, but according to the man page it
is supposed to do so.

[jacob navia]

Re: strtol library function


"Paul Emmons" <pemmons@voicen et.com> a écrit dans le message de
news:ddhfa0tlc0 4tf6a7lkvk35e43 b2harrnt3@4ax.c om...[color=blue]
> On Sat, 15 May 2004 12:51:16 -0400, Al Bowers <xabowers@rapid sys.com>
> wrote:[/color]
[snip][color=blue]
>
> It still seems rather strange to me that strtoul() accepts "-2" and
> returns 4294967294 without complaint, but according to the man page it
> is supposed to do so.
>[/color]

But HOW is that function supposed to know that
it was passed -2 and NOT 4294967294 ????

The binary representation of both is exactly the same!

[Ben Pfaff]

Re: strtol library function

"jacob navia" <jacob@jacob.re mcomp.fr> writes:
[color=blue]
> "Paul Emmons" <pemmons@voicen et.com> a écrit dans le message de
> news:ddhfa0tlc0 4tf6a7lkvk35e43 b2harrnt3@4ax.c om...[color=green]
>> On Sat, 15 May 2004 12:51:16 -0400, Al Bowers <xabowers@rapid sys.com>
>> wrote:[/color]
> [snip][color=green]
>>
>> It still seems rather strange to me that strtoul() accepts "-2" and
>> returns 4294967294 without complaint, but according to the man page it
>> is supposed to do so.[/color]
>
> But HOW is that function supposed to know that
> it was passed -2 and NOT 4294967294 ????[/color]

Because the first character of the string passed to it, following
whitespace is '-', or some locale-specific version thereof.
[color=blue]
> The binary representation of both is exactly the same![/color]

Their text representations differ.

Perhaps you should join Richard Heathfield's "reading for
comprehension" class.
--
Peter Seebach on C99:
"[F]or the most part, features were added, not removed. This sounds
great until you try to carry a full-sized printout of the standard
around for a day."

[those who know me have no need of my name]

Re: strtol library function

in comp.lang.c i read:
[color=blue]
>It still seems rather strange to me that strtoul() accepts "-2" and
>returns 4294967294 without complaint, but according to the man page it
>is supposed to do so.[/color]

for the same reason that assigning -2 to an unsigned long results in that
value.

--
a signature

[Dan Pop]

Re: strtol library function

In <m1zn87emj6.gnu s@usa.net> those who know me have no need of my name <not-a-real-address@usa.net > writes:
[color=blue]
>in comp.lang.c i read:
>[color=green]
>>It still seems rather strange to me that strtoul() accepts "-2" and
>>returns 4294967294 without complaint, but according to the man page it
>>is supposed to do so.[/color]
>
>for the same reason that assigning -2 to an unsigned long results in that
>value.[/color]

If it's the same reason, then when should strtoul() set errno to ERANGE
and why?

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

[Dan Pop]

Re: strtol library function

In <ddhfa0tlc04tf6 a7lkvk35e43b2ha rrnt3@4ax.com> Paul Emmons <pemmons@voicen et.com> writes:
[color=blue]
>It still seems rather strange to me that strtoul() accepts "-2" and
>returns 4294967294 without complaint, but according to the man page it
>is supposed to do so.[/color]

According to my reading of the C standard it isn't supposed to do so:

Returns

8 The strtol, strtoll, strtoul, and strtoull functions return
the converted value, if any. If no conversion could be performed,
zero is returned. If the correct value is outside the range of
^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^
representable values, LONG_MIN, LONG_MAX, LLONG_MIN, LLONG_MAX,
^^^^^^^^^^^^^^^ ^^^^^
ULONG_MAX, or ULLONG_MAX is returned (according to the return
type and sign of the value, if any), and the value of the macro
ERANGE is stored in errno.

Unless I'm missing something, -2 is outside the range of values that can
be represented by unsigned long. And any argument about "folding" it into
range would equally apply to values above ULONG_MAX, so this function
should NEVER set errno to ERANGE if that argument applied.

However, I know, from past discussions, that committee members disagree
with my interpretation.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

[Al Bowers]

Re: strtol library function



Dan Pop wrote:[color=blue]
> In <ddhfa0tlc04tf6 a7lkvk35e43b2ha rrnt3@4ax.com> Paul Emmons <pemmons@voicen et.com> writes:
>
>[color=green]
>>It still seems rather strange to me that strtoul() accepts "-2" and
>>returns 4294967294 without complaint, but according to the man page it
>>is supposed to do so.[/color]
>
>
> According to my reading of the C standard it isn't supposed to do so:
>
> Returns
>
> 8 The strtol, strtoll, strtoul, and strtoull functions return
> the converted value, if any. If no conversion could be performed,
> zero is returned. If the correct value is outside the range of
> ^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^
> representable values, LONG_MIN, LONG_MAX, LLONG_MIN, LLONG_MAX,
> ^^^^^^^^^^^^^^^ ^^^^^
> ULONG_MAX, or ULLONG_MAX is returned (according to the return
> type and sign of the value, if any), and the value of the macro
> ERANGE is stored in errno.
>
> Unless I'm missing something, -2 is outside the range of values that can
> be represented by unsigned long. And any argument about "folding" it into
> range would equally apply to values above ULONG_MAX, so this function
> should NEVER set errno to ERANGE if that argument applied.
>[/color]

I don't have the previous standard available but I believe the wording
for the description for strtoul was "If the subject sequence field
begins witha a minus sign, the value resulting from the conversion is
negated". Thus the function would first convert "-2" to, for example,
unsigned long x = 2, then it would be negated, x = -x. I can accept that
but I don't see this wording in the current standard, which, at least to
me, is confusing.

On a related issue, the current standard seems to support symmetry
between functions *scanf's and strotol, at least in regards to the
format of the expected subject sequence, yet doesn't show any support
for the symmetry in the resulting value. Most of the implementions that
I use, sscanf and strtoul will yield different results for the string
sequence "-2".

--
Al Bowers
Tampa, Fl USA
mailto: xabowers@myrapi dsys.com (remove the x to send email)

http://www.geocities.com/abowers822/

[Al Bowers]

Re: strtol library function



Al Bowers wrote:

[color=blue]
>
> On a related issue, the current standard seems to support symmetry
> between functions *scanf's and strotol, at least in regards to the
> format of the expected subject sequence, yet doesn't show any support
> for the symmetry in the resulting value. Most of the implementions that
> I use, sscanf and strtoul will yield different results for the string
> sequence "-2".[/color]

Oops, I meant "will yield a different result for the string
"4294967297 ", where the results are 4294967295 (ULONG_MAX) with
strtoul and 1 with sscanf.

--
Al Bowers
Tampa, Fl USA
mailto: xabowers@myrapi dsys.com (remove the x to send email)

http://www.geocities.com/abowers822/

[CBFalconer]

Re: strtol library function

Dan Pop wrote:[color=blue]
>[/color]
.... snip ...[color=blue]
>
> Unless I'm missing something, -2 is outside the range of values
> that can be represented by unsigned long. And any argument about
> "folding" it into range would equally apply to values above
> ULONG_MAX, so this function should NEVER set errno to ERANGE if
> that argument applied.[/color]

We had this argument right here and on comp.std.c a month or so
ago, and I took your side. I started it when I found that the
DJGPP implementation of strtoul did that quiet conversion. At any
rate, I got outshouted, and beaten into agreement that the action
was required by the standard.

I still think it is wrong, wrong, wrong, in fact wrong.

--
Chuck F (cbfalconer@yah oo.com) (cbfalconer@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!