whats the advantageof malloc over new in c++.

[Muzammil]

whats the beauty of "malloc" over "new" why its helpful for
programmer.for its own memory area.??

[Nick Keighley]

On 19 Aug, 09:52, Muzammil <muzammilPeer.. [e-mail] e:

whats the beauty of "malloc" over "new" why its helpful for
programmer.for *its own memory area.??

malloc() doesn't get used in C++ programs very much.
malloc() just allocates memory. new allocates memory
and constructs the object (by calling the constructor).
Placement new runs the constructor on the memory provided.

malloc() is mainly provided for historical compatibility
with C. new may use malloc() internally (it doesn't have to).

the main use for malloc(), I can see, is if memory is to
be passed to a C function and to be freed by the C function.
--
Nick Keighley

[tony_in_da_uk]

On Aug 19, 5:57 pm, Nick Keighley <nick_keighley_ nos...@hotmail. com>
wrote:

On 19 Aug, 09:52, Muzammil <muzammilPeer.. [e-mail] e:

whats the beauty of "malloc" over "new" why its helpful for
programmer.for its own memory area.??

malloc() doesn't get used in C++ programs very much.
malloc() just allocates memory. new allocates memory
and constructs the object (by calling the constructor).
Placement new runs the constructor on the memory provided.

malloc() is mainly provided for historical compatibility
with C. new may use malloc() internally (it doesn't have to).

the main use for malloc(), I can see, is if memory is to
be passed to a C function and to be freed by the C function.

+ malloc provides memory that _may_ be able to be grown using
realloc() without having to copy the content

+ new can be overridden to do all manner of things - which is normally
a good thing - but malloc() might occasionally be useful as a way to
bypass this (though you can't generally be sure that the "normal"
malloc function will receive your call - there are lots of ways of
installing alternatives)

+ you can free malloced memory without having the destructor called
(not normally a good idea, but may allow optimisations in certain
usages)

Still, the short story is don't use malloc/realloc and free unless you
find a reason to have to.

Tony

[=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?=]

On 2008-08-19 11:57, to***********@y ahoo.co.uk wrote:

On Aug 19, 5:57 pm, Nick Keighley <nick_keighley_ nos...@hotmail. com>
wrote:

>On 19 Aug, 09:52, Muzammil <muzammilPeer.. [e-mail] e:

whats the beauty of "malloc" over "new" why its helpful for
programmer.for its own memory area.??

malloc() doesn't get used in C++ programs very much.
malloc() just allocates memory. new allocates memory
and constructs the object (by calling the constructor).
Placement new runs the constructor on the memory provided.

malloc() is mainly provided for historical compatibility
with C. new may use malloc() internally (it doesn't have to).

the main use for malloc(), I can see, is if memory is to
be passed to a C function and to be freed by the C function.

+ malloc provides memory that _may_ be able to be grown using
realloc() without having to copy the content

Provided that the content of that memory does not have to be constructed.

--
Erik Wikström

[Juha Nieminen]

Erik Wikström wrote:

>+ malloc provides memory that _may_ be able to be grown using
realloc() without having to copy the content

Provided that the content of that memory does not have to be constructed.

You could always use placement new to construct that memory. (OTOH if
you must construct it, it starts making little sense to not to just use
'new' rather than 'malloc'.)

[Chris Becke]

"Muzammil" <mu************ *@gmail.comwrot e in message news:b1******** *************** ***********@56g 2000hsm.googleg roups.com...

whats the beauty of "malloc" over "new" why its helpful for
programmer.for its own memory area.??

memory allocated by malloc can be reallocated with realloc.
malloc doesnt throw an exception if the allocation fails.
Most runtimes implement a rich set of heap interrogation / debugging methods that can be usefull, which work principally on memory allocated with malloc.

[peter koch]

On 19 Aug., 11:59, "Chris Becke" <chris.be...@gm ail.comwrote:

"Muzammil" <muzammilPeer.. [e-mail] e in messagenews:b1* *************** *************** ***@56g2000hsm. googlegroups.co m...

whats the beauty of "malloc" over "new" why its helpful for
programmer.for *its own memory area.??

memory allocated by malloc can be reallocated with realloc.

But this is not really useful in a C++ context.

malloc doesnt throw an exception if the allocation fails.

Neither does new if you use the nothrow version (although I've
difficulties finding places, where I'd care about that).

Most runtimes implement a rich set of heap interrogation / debugging methods that can be
usefull, which work principally on memory allocated with malloc.

You can always base new on malloc if you want to - this allows you to
use the exact same methods, should they not already be available for
new/delete.
/Peter

[peter koch]

On 19 Aug., 10:52, Muzammil <muzammilPeer.. [e-mail] e:

whats the beauty of "malloc" over "new" why its helpful for
programmer.for *its own memory area.??

The only reason to use malloc is for interfacing with C.

/Peter

[Bo Persson]

Chris Becke wrote:

"Muzammil" <mu************ *@gmail.comwrot e in message
news:b1******** *************** ***********@56g 2000hsm.googleg roups.com...

>whats the beauty of "malloc" over "new" why its helpful for
programmer.f or its own memory area.??

memory allocated by malloc can be reallocated with realloc.

Which just sometimes might realloc in place, otherwise it has to copy
everything. And this doesn't work for anything with a constructor.

malloc doesnt throw an exception if the allocation fails.

A clear disadvantage. :-)

You have to check the result manually instead.

Most runtimes implement a rich set of heap interrogation /
debugging methods that can be usefull, which work principally on
memory allocated with malloc.

If you use std::vector you probably will never have to debug the
memory allocation at all.
Bo Persson

[tony_in_da_uk]

On Aug 20, 6:02 am, "Bo Persson" <[e-mail] te:

Chris Becke wrote:

"Muzammil" <muzammilPeer.. [e-mail] e in message
news:b1******** *************** ***********@56g 2000hsm.googleg roups.com...

whats the beauty of "malloc" over "new" why its helpful for
programmer.for its own memory area.??

memory allocated by malloc can be reallocated with realloc.

Which just sometimes might realloc in place, otherwise it has to copy
everything. And this doesn't work for anything with a constructor.

"just sometimes might" is trivialising the benefit a bit ;-). Anyway,
only the additional elements need then be manually constructed with
placement new... and this doesn't necessarily need to be done using a
default constructor before the meaningful values are available which
can be an advantage... so at least this two-step process can work for
some things with constructors.

Perhaps a bigger issue is that moved existing elements aren't copy
constructed so references/pointers stored therein may end up invalid.

Tony