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errno

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  errno "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-26 16:51 -0400
    Re: errno Eric Wolf <eric@boese-wolf.eu> - 2014-04-26 23:11 +0200
      Re: errno "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-26 17:17 -0400
        Re: errno Ike Naar <ike@iceland.freeshell.org> - 2014-04-26 22:35 +0000
          Re: errno "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-26 19:35 -0400
    Re: errno Richard <rgrdev_@gmail.com> - 2014-04-26 23:56 +0200
    Re: errno Barry Schwarz <schwarzb@dqel.com> - 2014-04-26 17:15 -0700
      Re: errno "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-26 20:23 -0400
        Re: errno "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-26 20:27 -0400
      Re: errno "Bill Cunningham" <nospam@nspam.invalid> - 2014-04-26 20:42 -0400

#43611 — errno

    My little utility doesn't print an errno value like it should. I have 
tried to fix it but have failed. I've never really used errno.h but always 
perror() so what am I doing wrong here.

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

int main(int argc, char *argv[])
{
    long int a;
    errno = 0;
    if ((a = strtol(argv[1], NULL, 16)) == -1)
        printf("%s\n", strerror(errno));
    printf("%d\n", a);
    return 0;
}

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#43612

First:

The line

>    printf("%d\n", a);

seems to be wrong. As a is long int, it should read

    printf("%ld\n", a);
             ^ mind the 'l'

Second:

As I understand 'man strtol' on my system, strtol sets errno only in
case of underflow or overflow, in which case it returns LONG_MIN or
respectively LONG_MAX.

So checking for -1 doesn't detect an error situation. You should
check for LONG_MAX and errno != 0 and LONG_MIN and errno != 0, or
simply errno != 0.

Posix manpage 'man 3posix strtol' on my system, says also a return value
of 0 could indicate an error if errno != 0 additionally.

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

int main(int argc, char *argv[])
{
    long int a;
    errno = 0;
    a = strtol(argv[1], NULL, 16);
    if (errno != 0)
        printf("%s\n", strerror(errno));
    printf("%ld\n", a);
    return 0;
}
 
Should print

Numerical result out of range
9223372036854775807

for in input of
999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999

Eric

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#43614

"Eric Wolf" <eric@boese-wolf.eu> wrote in message 
news:bs2lo7FsnqU1@mid.individual.net...
> First:
>
> The line
>
>>    printf("%d\n", a);
>
> seems to be wrong. As a is long int, it should read
>
>    printf("%ld\n", a);
>             ^ mind the 'l'

    Never really used long int either much.
  Usually go to atoi().

> Second:
>
> As I understand 'man strtol' on my system, strtol sets errno only in
> case of underflow or overflow, in which case it returns LONG_MIN or
> respectively LONG_MAX.
>
> So checking for -1 doesn't detect an error situation. You should
> check for LONG_MAX and errno != 0 and LONG_MIN and errno != 0, or
> simply errno != 0.
>
> Posix manpage 'man 3posix strtol' on my system, says also a return value
> of 0 could indicate an error if errno != 0 additionally.
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <errno.h>
> #include <string.h>
>
> int main(int argc, char *argv[])
> {
>    long int a;
>    errno = 0;
>    a = strtol(argv[1], NULL, 16);
>    if (errno != 0)
>        printf("%s\n", strerror(errno));
>    printf("%ld\n", a);
>    return 0;
> }
>
> Should print
>
> Numerical result out of range
> 9223372036854775807
>
> for in input of
> 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
>
> Eric

Thanks much! I typed

/h2d fffffffffffffff
And all that was printed was -1. I'm used to thinking that's an error but 
there is those few weird functions...

Bill

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#43618

On 2014-04-26, Bill Cunningham <nospam@nspam.invalid> wrote:
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <errno.h>
>> #include <string.h>
>>
>> int main(int argc, char *argv[])
>> {
>>    long int a;
>>    errno = 0;
>>    a = strtol(argv[1], NULL, 16);
>>    if (errno != 0)
>>        printf("%s\n", strerror(errno));
>>    printf("%ld\n", a);
>>    return 0;
>> }
> Thanks much! I typed
>
> /h2d fffffffffffffff
> And all that was printed was -1. I'm used to thinking that's an error but 
> there is those few weird functions...

That is why you should have used "%ld" instead of "%d" to
print the value of a. Had you used "%ld", the output would
not have been -1 but the equivalent of LONG_MAX.

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#43621

"Ike Naar" <ike@iceland.freeshell.org> wrote in message 
news:slrn3vfsllod5p.p4i.ike@iceland.freeshell.org...

> That is why you should have used "%ld" instead of "%d" to
> print the value of a. Had you used "%ld", the output would
> not have been -1 but the equivalent of LONG_MAX.

    Got it now. All I have really used was atoi and it doesn't return error. 
I might just go to errno.h instead of simple perror().

Bill

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#43617

"Bill Cunningham" <nospam@nspam.invalid> writes:

>     My little utility doesn't print an errno value like it should. I have 
> tried to fix it but have failed. I've never really used errno.h but always 
> perror() so what am I doing wrong here.
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <errno.h>
> #include <string.h>
>
> int main(int argc, char *argv[])
> {
>     long int a;
>     errno = 0;
>     if ((a = strtol(argv[1], NULL, 16)) == -1)
>         printf("%s\n", strerror(errno));
>     printf("%d\n", a);
>     return 0;
> }
>

0/10

Up yer game Bill. Even the regs who are chomping at the bit to show off
aren't biting anymore.

-- 
"Avoid hyperbole at all costs, its the most destructive argument on
the planet" - Mark McIntyre in comp.lang.c

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#43623

On Sat, 26 Apr 2014 16:51:17 -0400, "Bill Cunningham"
<nospam@nspam.invalid> wrote:

>    My little utility doesn't print an errno value like it should. I have 

Nowhere in your code do you attempt to print the value of errno.

>tried to fix it but have failed. I've never really used errno.h but always 
>perror() so what am I doing wrong here.
>
>#include <stdio.h>
>#include <stdlib.h>
>#include <errno.h>
>#include <string.h>
>
>int main(int argc, char *argv[])
>{
>    long int a;
>    errno = 0;
>    if ((a = strtol(argv[1], NULL, 16)) == -1)

According to your follow-up message, argv[1] is a string consisting of
15 f's.  Under what conditions do you think this would ever produce a
value of -1?  (You should read the description of strtol and determine
the only situation when it can produce a negative value.)

What is the size of long int on your system?  How did you determine
this?

>        printf("%s\n", strerror(errno));

What makes you think errno was set by anything your program did?

>    printf("%d\n", a);

This undefined behavior has been addressed by others.

>    return 0;
>}
>

-- 
Remove del for email

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#43624

"Barry Schwarz" <schwarzb@dqel.com> wrote in message 
news:dsgol9h34hqo6q4jk00fl6boj6mneb6n4v@4ax.com...
> On Sat, 26 Apr 2014 16:51:17 -0400, "Bill Cunningham"
> <nospam@nspam.invalid> wrote:
>
>>    My little utility doesn't print an errno value like it should. I have
>
> Nowhere in your code do you attempt to print the value of errno.
>
>>tried to fix it but have failed. I've never really used errno.h but always
>>perror() so what am I doing wrong here.
>>
>>#include <stdio.h>
>>#include <stdlib.h>
>>#include <errno.h>
>>#include <string.h>
>>
>>int main(int argc, char *argv[])
>>{
>>    long int a;
>>    errno = 0;
>>    if ((a = strtol(argv[1], NULL, 16)) == -1)
>
> According to your follow-up message, argv[1] is a string consisting of
> 15 f's.  Under what conditions do you think this would ever produce a
> value of -1?  (You should read the description of strtol and determine
> the only situation when it can produce a negative value.)
>
> What is the size of long int on your system?  How did you determine
> this?
>
>>        printf("%s\n", strerror(errno));
>
> What makes you think errno was set by anything your program did?
>
>>    printf("%d\n", a);
>
> This undefined behavior has been addressed by others.
>
>>    return 0;
>>}

    Works fine now. I've never used strtol or strtoll. I have occasssionally 
used strtod and had great success. errno seems to set to ERANGE now when I 
intentionally try to over or underflow. I am in the habit of -1 as in most 
*nix sys calls being an error. I admit I should've look closer at the man 
page.

Bill

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#43625

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

int main(int argc, char *argv[])
{
    long int a;
    errno = 0;
    if ((a = strtol(argv[1], NULL, 16)) != 0)
        printf("%s\n", strerror(errno));
    printf("%ld\n", a);
    return 0;
}

    Works as it appears anyway. Who knows what subtle bug might be lurking.

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#43626

"Barry Schwarz" <schwarzb@dqel.com> wrote in message

> What is the size of long int on your system?
[...]

Oh yeah ok sorry. Looks like a long and long long are 64 bits while an int 
is 32 bit.

Bill

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