Array Out Of Boundaries

[krish]

int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this

[kondal]

krish wrote:

int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this.

Hey, the indexing starts from 0. So you have 5 elements in the array
starting from 0 to 4. So k[5] would be 6th element outside the bounds
of the array.

-kondal

[krish]

kondal wrote:

krish wrote:

int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this.

Hey, the indexing starts from 0. So you have 5 elements in the array
starting from 0 to 4. So k[5] would be 6th element outside the bounds
of the array.

-kondal

That is understood .But how come j is printing the value 50 here all
the time or what ever value you are assigning.

[Richard Heathfield]

krish said:

kondal wrote:

>krish wrote:

int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this.

Hey, the indexing starts from 0. So you have 5 elements in the array
starting from 0 to 4. So k[5] would be 6th element outside the bounds
of the array.

-kondal

That is understood .But how come j is printing the value 50 here all
the time or what ever value you are assigning.

What value did you expect j to have?

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[krish]

Richard Heathfield wrote:

krish said:

kondal wrote:

krish wrote:
int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this.

Hey, the indexing starts from 0. So you have 5 elements in the array
starting from 0 to 4. So k[5] would be 6th element outside the bounds
of the array.

-kondal

That is understood .But how come j is printing the value 50 here all
the time or what ever value you are assigning.

What value did you expect j to have?

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

Some garbage value...But it is showing the values I am assigning there
in the line K[5]= 50

[Ian Collins]

krish wrote:

Richard Heathfield wrote:

>>krish said:

>>>kondal wrote:

krish wrote:

>int main()
>{
>
int i,j;
>int k[]={1,2,3,4,5};
>k[5]=50;
>printf("%d %d",i,j);
>}
>
>This program is compiling fine and the result is -858993460 50
>I am unable to find why this is printing the above value. Request help
>on this.

Hey, the indexing starts from 0. So you have 5 elements in the array
starting from 0 to 4. So k[5] would be 6th element outside the bounds
of the array.

-kondal

That is understood .But how come j is printing the value 50 here all
the time or what ever value you are assigning.

What value did you expect j to have?

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

Some garbage value...But it is showing the values I am assigning there
in the line K[5]= 50

You're invoking the demon known as undefined behaviour, your 50 is just
a facet of the layout of your automatic variables.

--
Ian Collins.

[Default User]

krish wrote:

>
kondal wrote:

krish wrote:

int main()
{
>
int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);

That is understood .But how come j is printing the value 50 here all
the time or what ever value you are assigning.

You've created undefined behavior, ANYTHING can happen. In this case,
you're likely writing into the space occupied by j when do that illegal
access.

Why are you doing this? Such tests tell you nothing. There is no
defined behavior for undefined behavior.

Brian

[Richard Heathfield]

krish said:

>
Richard Heathfield wrote:

>krish said:

<snip>

But how come j is printing the value 50 here all
the time or what ever value you are assigning.

What value did you expect j to have?

Some garbage value...

And that's what it has. So your expectations were met.

But it is showing the values I am assigning there
in the line K[5]= 50

Garbage is garbage. Any apparent patterns you see therein are meaningless,
especially when the program has other errors (such as the reference to
k[5], which does not exist).

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

[kondal]

krish wrote:

kondal wrote:

krish wrote:

int main()
{
>
int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}
>
>
>
This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this.

Hey, the indexing starts from 0. So you have 5 elements in the array
starting from 0 to 4. So k[5] would be 6th element outside the bounds
of the array.

-kondal

That is understood .But how come j is printing the value 50 here all
the time or what ever value you are assigning.

You are experiencing what is called 'buffer overflow'.

First the three variables are in stack starting with i, j, k[] one
after the other. This could be compiler and operating system specific.
What I see is that k[5] is the location for j and k[6] would be the
location for i. K[7] would probably would be the return address.

This is the same concept what hackers do during the shell coding,
modifying the return address to point to an inserted function.

This scenario would not work for all compilers ot operating systems.

-kondal

[Keith Thompson]

"krish" <kr************@gmail.comwrites:

int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this

You invoke undefined behavior by assigning to k[5].

You invoke undefined behavior by accessing the values of i and j,
which are uninitialized.

You invoke undefined behavior by calling printf() with no visible
prototype (you need to add "#include <stdio.h>").

Possibly your compiler happens to place j just after k. Another
compiler might do something else.

Analyzing the specific results of undefined behavior can sometimes be
useful in figuring out why a program is failing. Once you've figured
that out, the next step is to correct the program.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[jmcgill]

krish wrote:

int k[]={1,2,3,4,5};
k[5]=50;

You are accessing the sixth element of a five element array.

[jmcgill]

krish wrote:

>> int i,j;
int k[]={1,2,3,4,5};
k[5]=50;

That is understood .But how come j is printing the value 50 here all
the time or what ever value you are assigning.

You are getting lucky with undefined behavior.

Apparently, on your system, in the runs you have checked, the storage of
j is just beyond the last element of the array. Or it may be some
unrelated "50". Who knows if these things are related at all?

[Robert Seacord]

krish wrote:

response below.

int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this

i'm guessing because when you wrote past the end of the array you
overwrote the value of j with the value 50, but the value of i is
uninitialized so you are getting garbage.

rCs

[Mark McIntyre]

On 25 Sep 2006 00:00:21 -0700, in comp.lang.c , "krish"
<kr************@gmail.comwrote:

>int main()
{

int i,j;
int k[]={1,2,3,4,5};
k[5]=50;
printf("%d %d",i,j);
}

This program is compiling fine and the result is -858993460 50
I am unable to find why this is printing the above value. Request help
on this

There is no element [5], so you're writing to memory that doesn't
belong to you. The result of this is undefined, and anything could
happen, including crashing your programme.

Rembember C array start at 1.
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

[Mark McIntyre]

On 25 Sep 2006 00:32:22 -0700, in comp.lang.c , "krish"
<kr************@gmail.comwrote:

>
Richard Heathfield wrote:

the time or what ever value you are assigning.

Some garbage value...But it is showing the values I am assigning there
in the line K[5]= 50

The value you're seeing /is/ garbage.

It just so happens that your particular compiler arranges the
automatic variables in in such a way, and in debug mode is kind enough
to let you write over them. This is probably a Bad Thing.

This tricked you into thinking you were getting a 'good' value. Try
turning off debug mode and rebuilding it.

--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

[Walter Roberson]

In article <b3********************************@4ax.com>,
Mark McIntyre <ma**********@spamcop.netwrote:

>Rembember C array start at 1.

You're just checking to see if we're awake, right Mark?
--
If you lie to the compiler, it will get its revenge. -- Henry Spencer

[kondal]

Mark McIntyre wrote:

Rembember C array start at 1.

I wonder what you mean by this statement. In C the indexing starts from
0.

-kondal

[Mark McIntyre]

On Mon, 25 Sep 2006 23:19:47 +0000 (UTC), in comp.lang.c ,
ro******@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote:

>In article <b3********************************@4ax.com>,
Mark McIntyre <ma**********@spamcop.netwrote:

>>Rembember C array start at 1.

You're just checking to see if we're awake, right Mark?

Grin. I meant to type "don't" in there somewhere...

Mind you, you're the only person who does seem to be awake...
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan