A very simple question

[Marmagya]

Hi,
Why should the following code give me a core dump?

#include <stdio.h>

int main(){
char *a="Marmagya";

printf("The statement is : %s", *a);

return 0;
}
Regards
Marmagya

[Joona I Palaste]

Marmagya <ma******@epatr a.com_nospam> scribbled the following:

Hi,
Why should the following code give me a core dump? #include <stdio.h> int main(){
char *a="Marmagya"; printf("The statement is : %s", *a);
%s expects a pointer, and then starts reading from where that pointer
points onwards until it hits a 0 byte. You're giving it a char 'M'
instead. This makes %s treat the 'M' as a pointer, and tries to read
where it points to. But which address 'M' translates to is undefined
behaviour, and it is most likely that address doesn't even belong to
you. So you get a core dump.
Fix the problem by giving %s what it wants: a pointer.

printf("The statement is : %s", a);
return 0;
}

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ---------------------------\
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| http://www.helsinki.fi/~palaste W++ B OP+ |
\----------------------------------------- Finland rules! ------------/
"You will be given the plague."
- Montgomery Burns

[Chris Dollin]

Marmagya wrote:

Why should the following code give me a core dump?

#include <stdio.h>

int main(){
char *a="Marmagya";
printf("The statement is : %s", *a);
return 0;
}

There's no "should" about it; it's undefined behaviour, so the
implementation can do what it likes, including ignoring it, printing
your string, printing a different string, or painting your toenails
purple. Luckily, your implementation falls into a core dump.

%s wants a string. *a is a character (viz, 'M'). BOOM today.

Perhaps you meant just `a`.

[Doesn't your compiler warn you about this line? GCC will, if
suitably provoked.]

--
Chris "electric hedgehog" Dollin
C FAQs at: http://www.faqs.org/faqs/by-newsgrou...mp.lang.c.html
C welcome: http://www.angelfire.com/ms3/bchambl...me_to_clc.html

[Dan Pop]

In <bf**********@o ravannahka.hels inki.fi> Joona I Palaste <pa*****@cc.hel sinki.fi> writes:

Marmagya <ma******@epatr a.com_nospam> scribbled the following:

Hi,
Why should the following code give me a core dump?

#include <stdio.h>

int main(){
char *a="Marmagya";

printf("The statement is : %s", *a);

Fix the problem by giving %s what it wants: a pointer.

printf("The statement is : %s", a);

return 0;
}

People with a clue, or even half of one, also provide the required newline
character:

printf("The statement is : %s\n", a);

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

[Chris Dollin]

Dan Pop wrote:

In <bf**********@m urdoch.hpl.hp.c om> Chris Dollin <ke**@hpl.hp.co m>
writes:

%s wants a string. *a is a character (viz, 'M'). BOOM today.

*a is a character, 'M' isn't!

Yes it is - it just isn't a char. (This game brought to you by Nitpicks
Anonymous.)

Perhaps you meant just `a`.

Perhaps he just meant a ;-) Yeah, properly referring to single letter
identifiers in plain text is a real pain.

Especially `a`. Perhaps systematically renaming his code so that the
variable was called A would have worked ...
People with OP's degree of cluelessness seldom know how to use their
compilers. When you're making your first steps in C, where should you
invest your time and effort: in your C tutorial text or in the reference
manual of your compiler? The answer is far from obvious and the net
result is that it is the advanced programmers who know how to invoke
their compilers in a newbie-friendly fashion :-)

Yes. Oh, the joys of irony.

--
Chris "iron hedgehogy" Dollin
C FAQs at: http://www.faqs.org/faqs/by-newsgrou...mp.lang.c.html
C welcome: http://www.angelfire.com/ms3/bchambl...me_to_clc.html

[Dan Pop]

In <bf**********@m urdoch.hpl.hp.c om> Chris Dollin <ke**@hpl.hp.co m> writes:

Dan Pop wrote:

In <bf**********@m urdoch.hpl.hp.c om> Chris Dollin <ke**@hpl.hp.co m>
writes:

%s wants a string. *a is a character (viz, 'M'). BOOM today.

*a is a character, 'M' isn't!

Yes it is - it just isn't a char. (This game brought to you by Nitpicks
Anonymous.)

3.7.1
1 character
single-byte character
<C> bit representation that fits in a byte

There aren't many hosted implementations where the representation of an
int fits in a byte.

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

[Mark McIntyre]

On Wed, 16 Jul 2003 16:20:24 +0100, in comp.lang.c , Chris Dollin
<ke**@hpl.hp.co m> wrote:

Are there any where the representation of 'M' doesn't fit into a byte?

There aren't allowed to be any. But you knew that already.

--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.angelfire.c om/ms3/bchambless0/welcome_to_clc. html>
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[sunil]

Marmagya <ma******@epatr a.com_nospam> wrote in message news:<H_******* *****@news.orac le.com>...

Hi,
Why should the following code give me a core dump?

#include <stdio.h>

int main(){
char *a="Marmagya";

printf("The statement is : %s", *a); Because *a is a character 'M' in this case and the compiler generates
code to print the string with address as ASCII value of 'M' (0x4d) and
you are probably not allowed to access that section of memory. You can
verify this using a debugger like GDB on Linux. Anyways its supposed
to be a as %s translates to print the string whose first character is
at address specified (a) till you encounter '\0'.
Cheers,
Sunil.
return 0;
}
Regards
Marmagya

[Richard Heathfield]

pete wrote:

Chris Dollin wrote:

Dan Pop wrote:

> In <bf**********@m urdoch.hpl.hp.c om> Chris Dollin <ke**@hpl.hp.co m>
> writes:
>>Dan Pop wrote:
>>> In <bf**********@m urdoch.hpl.hp.c om>
>>> Chris Dollin <ke**@hpl.hp.co m>
>>> writes: >>>>%s wants a string. *a is a character (viz, 'M'). BOOM today.
>>>
>>> *a is a character, 'M' isn't!
>>
>>Yes it is - it just isn't a char.
>> (This game brought to you by Nitpicks Anonymous.)

'M' is a character constant.

And character constants are integers. An odd little corner of C, that. It's
worth blowing the dust off it every few months.

--
Richard Heathfield : bi****@eton.pow ernet.co.uk
"Usenet is a strange place." - Dennis M Ritchie, 29 July 1999.
C FAQ: http://www.eskimo.com/~scs/C-faq/top.html
K&R answers, C books, etc: http://users.powernet.co.uk/eton

[Dan Pop]

In <bf**********@m urdoch.hpl.hp.c om> Chris Dollin <ke**@hpl.hp.co m> writes:

Dan Pop wrote:

In <bf**********@m urdoch.hpl.hp.c om> Chris Dollin <ke**@hpl.hp.co m>
writes:

Dan Pop wrote:

In <bf**********@m urdoch.hpl.hp.c om> Chris Dollin <ke**@hpl.hp.co m>
writes:
>%s wants a string. *a is a character (viz, 'M'). BOOM today.

*a is a character, 'M' isn't!

Yes it is - it just isn't a char. (This game brought to you by Nitpicks
Anonymous. )

3.7.1
1 character
single-byte character
<C> bit representation that fits in a byte

There aren't many hosted implementations where the representation of an
int fits in a byte.

Are there any where the representation of 'M' doesn't fit into a byte?

Sure: how do you expect to fit a 16-bit representation or a 32-bit
representation of M into the 8 bits of the vanilla byte?

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