difference between calloc() and malloc()

[manish sahu]

difference between calloc() and malloc()

[=?utf-8?Q?David_C=C3=B4me?=]

On Wed, 13 Feb 2008 20:49:47 +0100, manish sahu <ro********@yahoo.com>
wrote:

difference between calloc() and malloc()

RTFM

[Christopher]

On Feb 13, 1:49 pm, manish sahu <[e-mail]:

difference between calloc() and malloc()

You shouldn't be using either one in C++ if you can help it. Use
operator new instead.

[acehreli]

On Feb 13, 11:56 am, Christopher <[e-mail]:

On Feb 13, 1:49 pm, manish sahu <[e-mail]:

difference between calloc() and malloc()

You shouldn't be using either one in C++ if you can help it. Use
operator new instead.

new constructs objects but malloc and calloc reserve raw memory;
different...

Ali

[Victor Bazarov]

ac******@gmail.com wrote:

On Feb 13, 11:56 am, Christopher <[e-mail]:

>On Feb 13, 1:49 pm, manish sahu <[e-mail]:

>>difference between calloc() and malloc()

You shouldn't be using either one in C++ if you can help it. Use
operator new instead.

new constructs objects but malloc and calloc reserve raw memory;
different...

Well, malloc and calloc are just 'new char[]' and 'new char[]()'.
They don't "reserve raw memory" since there is no "raw memory" in
C++.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[acehreli]

On Feb 13, 12:42 pm, "Victor Bazarov" <[e-mail]:

[e-mail] wrote:

On Feb 13, 11:56 am, Christopher <[e-mail]:

On Feb 13, 1:49 pm, manish sahu <[e-mail]:

>difference between calloc() and malloc()

You shouldn't be using either one in C++ if you can help it. Use
operator new instead.

new constructs objects but malloc and calloc reserve raw memory;
different...

Well, malloc and calloc are just 'new char[]' and 'new char[]()'.
They don't "reserve raw memory" since there is no "raw memory" in
C++.

With "raw memory," I meant the allocated storage that allocators
allocate; you know, to construct objects on... I don't keep a copy of
the standard any more, but I'm pretty sure it talks about storage. I
regret now that I called that "raw memory"...

On your point about using new[] for storage, it is misguided. Because
new char[] allocates uninitialized chars and new char[]() allocates
initialized chars. The behaviour is quite different than allocating
storage to construct objects on. It is possible to construct object on
tops of chars, but it's a side effect of chars having trivial
destructors.

Ali

[acehreli]

On Feb 13, 1:46 pm, [e-mail] wrote:

On your point about using new[] for storage, it is misguided. Because
new char[] allocates uninitialized chars and new char[]() allocates
initialized chars.

Even though I typed "allocates" twice above, I meant "constructs"
twice. My point below is that new[] constructs chars.

The behaviour is quite different than allocating
storage to construct objects on. It is possible to construct object on
tops of chars, but it's a side effect of chars having trivial
destructors.

Ali

[Daniel T.]

manish sahu <ro********@yahoo.comwrote:

difference between calloc() and malloc()

From http://www.dinkumware.com/manuals/default.aspx

calloc
void *calloc(size_t nelem, size_t size);
The function allocates an array object containing nelem elements each of
size size, stores zeros in all bytes of the array, and returns the
address of the first element of the array if successful; otherwise, it
returns a null pointer.

malloc
void *malloc(size_t size);
The function allocates an object of size size, and returns the address
of the object if successful; otherwise, it returns a null pointer.

See the difference?

[James Kanze]

On Feb 13, 9:42 pm, "Victor Bazarov" <[e-mail]:

[e-mail] wrote:

On Feb 13, 11:56 am, Christopher <[e-mail]:

On Feb 13, 1:49 pm, manish sahu <[e-mail]:

>difference between calloc() and malloc()

You shouldn't be using either one in C++ if you can help it. Use
operator new instead.

new constructs objects but malloc and calloc reserve raw memory;
different...

Well, malloc and calloc are just 'new char[]' and 'new
char[]()'. They don't "reserve raw memory" since there is no
"raw memory" in C++.

That's not true. Raw memory is what exists between the moment
the memory is allocated, and the moment the constructor is run,
or between the moment the destructor finishes and the moment the
memory is freed. Call reserve() on an empty std::vector, and
that vector will contain raw memory.

The way raw memory is usually allocated in C++ is by calling the
operator new() function. malloc() can also be used. calloc()
should probably be avoided, both in C and in C++, because it
masks a number of serious errors.

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[Jeff Schwab]

James Kanze wrote:

The way raw memory is usually allocated in C++ is by calling the
operator new() function. malloc() can also be used. calloc()
should probably be avoided, both in C and in C++, because it
masks a number of serious errors.

What are the problems with calloc? Googling "calloc errors" and
"problems with calloc" did not turn up anything obvious.

[Pete Becker]

On 2008-02-14 13:09:06 -0500, Jeff Schwab <je**@schwabcenter.comsaid:

James Kanze wrote:

>The way raw memory is usually allocated in C++ is by calling the
operator new() function. malloc() can also be used. calloc()
should probably be avoided, both in C and in C++, because it
masks a number of serious errors.

What are the problems with calloc? Googling "calloc errors" and
"problems with calloc" did not turn up anything obvious.

It sets all the bytes in the allocated memory to 0. All too often, that
will mean that uninitialized data members look like they have
legitimate values.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Jack Klein]

On Thu, 14 Feb 2008 14:03:46 -0500, Pete Becker
<pe**@versatilecoding.comwrote in comp.lang.c++:

On 2008-02-14 13:09:06 -0500, Jeff Schwab <je**@schwabcenter.comsaid:

James Kanze wrote:

The way raw memory is usually allocated in C++ is by calling the
operator new() function. malloc() can also be used. calloc()
should probably be avoided, both in C and in C++, because it
masks a number of serious errors.

What are the problems with calloc? Googling "calloc errors" and
"problems with calloc" did not turn up anything obvious.

It sets all the bytes in the allocated memory to 0. All too often, that
will mean that uninitialized data members look like they have
legitimate values.

....as opposed to producing undefined value when the uninitialized data
members are read to determine whether they are valid?

I'll admit that calloc() is not often useful in either C or C++, but
there are occasional times when it, even in C++.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://c-faq.com/
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++
http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html

[James Kanze]

On Feb 14, 7:09 pm, Jeff Schwab <[e-mail]:

James Kanze wrote:

The way raw memory is usually allocated in C++ is by calling the
operator new() function. malloc() can also be used. calloc()
should probably be avoided, both in C and in C++, because it
masks a number of serious errors.

What are the problems with calloc?

Using uninitialized memory is an error. Calloc sets all of the
bytes to 0, which happens to correspond to zero initialization
on a lot of systems BUT is not necessarily the case. If your
code counts on zero initialization, using calloc will typically
mask the error (until you have to port to a machine where null
pointers aren't all 0 bits, or some such).

A more reasonable choice would be to initialize all of the
memory with some easily identifiable pattern which probably
won't work---0xDEADBEEF is a popular choice.

An even more reasonable choice, of course, is to use new:-).

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[Ron Natalie]

Victor Bazarov wrote:

ac******@gmail.com wrote:

>On Feb 13, 11:56 am, Christopher <[e-mail]:

>>On Feb 13, 1:49 pm, manish sahu <[e-mail]:

difference between calloc() and malloc()
You shouldn't be using either one in C++ if you can help it. Use
operator new instead.

new constructs objects but malloc and calloc reserve raw memory;
different...

Well, malloc and calloc are just 'new char[]' and 'new char[]()'.
They don't "reserve raw memory" since there is no "raw memory" in
C++.

V

The are NOT just new char[].
They allocate chars from the C library free store.
The only difference with calloc is that it multiples the two args
together (this is one those attrocious carry over's from the so-called
portable IO library like the stdio funcs that should have never been
adopted by any sane language) and zeros the returned memory.

Your C++ allocation functions might allocate from the same arena, then
again they might not.