far pointers

[Harsimran]

Can any one explain what are far pointers and what is the difference
between malloc and calloc .Which is better ?

[Joona I Palaste]

Harsimran <sa************ @yahoo.co.in> scribbled the following:

Can any one explain what are far pointers and what is the difference
between malloc and calloc .Which is better ?

Far pointers are not an ISO standard C concept and are thus off-topic
here. There are two differences between malloc and calloc:
1) malloc excepts one parameter, calloc excepts two. The size that
calloc allocates is the parameters multiplied together.
2) calloc automatically zeroes the allocated memory, malloc does not.

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\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
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[Chris Torek]

In article <news:b8******* *************** ****@posting.go ogle.com>
Harsimran <sa************ @yahoo.co.in> wrote:

Can any one explain what are far pointers ...
There are no such things. (See the comp.lang.c FAQ, question 19.40d.)
and what is the difference between malloc and calloc .Which is better ?

Which is better, chocolate or strawberry; coconut or soy sauce;
a hammer or a wrench?

A call of the form malloc(n) returns either NULL (failure) or a
pointer to the first of n contiguous bytes. A call of the form
calloc(nitems, size) returns either NULL (failure) or a pointer
to the first of nitems*size contiguous bytes, after also calling
memset() to set all those bytes to '\0'.

If you need bytes pre-set to '\0' you can use calloc(); if you just
need bytes, use malloc().
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email: forget about it http://web.torek.net/torek/index.html
Reading email is like searching for food in the garbage, thanks to spammers.

[Mabden]

"Chris Torek" <no****@torek.n et> wrote in message
news:cf******** @news3.newsguy. com...

In article <news:b8******* *************** ****@posting.go ogle.com>
Harsimran <sa************ @yahoo.co.in> wrote:

and what is the difference between malloc and calloc .Which is better ?
Which is better, chocolate or strawberry; coconut or soy sauce;
a hammer or a wrench?

I'd rather be hammered than wrenched...

Coconut sauce???
If you need bytes pre-set to '\0' you can use calloc(); if you just
need bytes, use malloc().

Right, if you are going to malloc() some space then set it all to zero, you
might as well just use calloc(). This can sometimes be the "coward's way
out". If you don't think you can handle using your memory properly, and have
errors in calculating addresses where you are "one off", it's nice to have
the safety net of a zeroed out chunk of memory - no random values. For
instance, when storing strings in malloc'ed memory, if you forget the
terminating '\0', the calloc assures it is already there. So what I'm saying
is calloc() can hide subtle bugs and overruns, so the program may work, but
still have bugs.
I sometimes used calloc in beginning development, to get going, and switched
back to malloc to find bugs and overruns for the real code. But that was a
long time ago - now I want to know right away.

Can anyone come up with a good reason to zero out "raw" memory before you've
even used it? ...maybe to make sure there are zeroes in the empty
byte-aligned null space???

--
Mabden
p.s. I've been wrong before...

[Jens.Toerring]

Mabden <mabden@sbc_glo bal.net> wrote:

Can anyone come up with a good reason to zero out "raw" memory before you've
even used it? ...maybe to make sure there are zeroes in the empty
byte-aligned null space???

Needing an array of ints (or long ints) with all elements initialized
to 0 is more or less the only time I use calloc().

Regards, Jens
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\ Jens Thoms Toerring ___ Je***********@p hysik.fu-berlin.de
\______________ ____________ http://www.toerring.de

[pete]

Harsimran wrote:

Can any one explain what are far pointers
It may have something to do with Borland.
and what is the difference
between malloc and calloc .Which is better ?

I use calloc when I want to allocate memory filled
with zero value bytes. That's what calloc is for.

--
pete

[Emmanuel Delahaye]

pete wrote on 12/08/04 :

Can any one explain what are far pointers

It may have something to do with Borland.

Not only. It has somehing to do with x86 arch in real mode.

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html

"C is a sharp tool"

[CBFalconer]

Je***********@p hysik.fu-berlin.de wrote:

Mabden <mabden@sbc_glo bal.net> wrote:

Can anyone come up with a good reason to zero out "raw" memory
before you've even used it? ...maybe to make sure there are
zeroes in the empty byte-aligned null space???

Needing an array of ints (or long ints) with all elements
initialized to 0 is more or less the only time I use calloc().

While that may work for you, it is not guaranteed by the standard.

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

[CBFalconer]

Joona I Palaste wrote:

Harsimran <sa************ @yahoo.co.in> scribbled the following:

Can any one explain what are far pointers and what is the difference
between malloc and calloc .Which is better ?
Far pointers are not an ISO standard C concept and are thus off-topic
here. There are two differences between malloc and calloc:
1) malloc excepts one parameter, calloc excepts two. The size that

^^^^^^^ ^^^^^^^
accepts :-)
calloc allocates is the parameters multiplied together.
2) calloc automatically zeroes the allocated memory, malloc does not.

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

[Arthur J. O'Dwyer]

On Thu, 12 Aug 2004, CBFalconer wrote:

Je***********@p hysik.fu-berlin.de wrote:

Needing an array of ints (or long ints) with all elements
initialized to 0 is more or less the only time I use calloc().

While that may work for you, it is not guaranteed by the standard.

Amplification (sorry!;) : memsetting an 'int' to zero is not
guaranteed by the Standard to set the actual /value/ of that 'int'
to the integer zero. (But I think there's some debate about that;
I forget the details.) So what Jens is suggesting doesn't work.

However, unsigned types are guaranteed to have pure binary
representations , which means that memsetting an 'unsigned int' to
zero /will/ set its value to the unsigned integer zero! Ditto
'unsigned char', 'unsigned long', et cetera. (And I think ditto
the new C99 fixed-width types: 'int32_t' and 'int_least8_t' and
friends.)

I often use 'calloc' in image processing; for example, to get
a grayscale image of size w*h initialized to black, I'll write

unsigned char *im = calloc(w*h, 1);

So 'calloc' does have its uses; they're just rare.

-Arthur