Strange thing about malloc()

[Ronny Mandal]

Hi!

I am writing a program that'll read binary integers from a file, put them
into a dynamic array. THe array is first declared

int* a = malloc( sizeof( int ) * N ) <-- N is the number of slots.

When N is odd, the program will work just fine, however when N is even, it
will not work.

Is it just a Win32-issue, or a bug?

--

Regards,

Ronny Mandal
This e-mail and any attachment are confidential and may be privileged or
otherwise protected from disclosure. It is solely intended for the person(s)
named above. If you are not the intended recipient, any reading, use,
disclosure, copying or distribution of all or parts of this e-mail or
associated attachments is strictly prohibited. If you are not an intended
recipient, please notify the sender immediately by replying to this message
or by telephone and delete this e-mail and any attachments permanently from
your system.

[Flash Gordon]

Ronny Mandal wrote:

Hi!

I am writing a program that'll read binary integers from a file, put them
into a dynamic array. THe array is first declared

int* a = malloc( sizeof( int ) * N ) <-- N is the number of slots.

When N is odd, the program will work just fine, however when N is even, it
will not work.

Is it just a Win32-issue, or a bug?

There is almost certainly a bug somewhere in *your* code, my guess would
be overrunning the buffer you have created. Reduce your program to the
smallest compilable example that exhibits the problem and does not use
extensions and post it here and you might get some help.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.

[Ronny Mandal]

Sorry about the footer, sometimes I forget to remove it, it comes
automatically, but not on my personal behalf.

Indeed, it is not my typing.

[Keith Thompson]

Jonathan Bartlett <jo*****@eskimo .com> writes:

If you're interested in the workings of malloc(), you should check out this:

http://www.ibm.com/developerworks/li...rary/l-memory/

Correction: If you're interested in the workings of some
system-specific implementations of malloc().

--
Keith Thompson (The_Other_Keit h) 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.

[Christian Bau]

In article <d4**********@r eadme.uio.no>,
"Ronny Mandal" <ro*****@math.u io.no> wrote:

Hi!

I am writing a program that'll read binary integers from a file, put them
into a dynamic array. THe array is first declared

int* a = malloc( sizeof( int ) * N ) <-- N is the number of slots.

When N is odd, the program will work just fine, however when N is even, it
will not work.

Is it just a Win32-issue, or a bug?

Have a good look at your code. Are you by any chance writing to a [N] ?
Assuming that malloc () was successful, you are allowed to write to a
[0] up to a [N-1], but not a [N].

[Richard Bos]

ri*****@cogsci. ed.ac.uk (Richard Tobin) wrote:

In article <3c************ *@individual.ne t>,
Artie Gold <ar*******@aust in.rr.com> wrote:

That part of the sig is likely put there by the server through which the
message was posted. It's probably not the OP's fault.

Quite so, but if we don't complain to people who use such servers, how
are they ever going to be replaced?

If, by choice, you use a server that adds this sort of thing to your
message, it makes you look silly. If you work for a company that puts
it on all your outgoing messages, it makes your company look as if
they don't understand the net, and are probably the sort who spend
more money on lawyers than products.

IOW, like Microsoft ;-)

Richard

[Ronny Mandal]

Thanks for helping me out, strange thing that I just *forgot* that a[N]
holds N-1 elements. malloc worked just fine from the beginning.

Ronny Mandal

[Alan Balmer]

On Fri, 22 Apr 2005 00:35:40 +0200, "Ronny Mandal"
<ro*****@math.u io.no> wrote:

Thanks for helping me out, strange thing that I just *forgot* that a[N]
holds N-1 elements. malloc worked just fine from the beginning.

Um, not exactly. When you have
int* a = malloc( sizeof( int ) * N ) ;

a can hold N elements, but the first one is a[0] and the last one is
a[N-1].

Probably what you meant.

--
Al Balmer
Balmer Consulting
re************* ***********@att .net