Best way to allocate raw memory (char buffer) ?
Robert O'Dowd
>
> Which is the best and most efficient way to allocate and free
> large amounts of raw memory in C++, e.g. for a graphics buffer.
>
> Lets say I want to allocate/free a char array. I know three ways
> how to do that:
>
> Method 1:
> char *buffer = new char[BUFSIZE];
> delete[] buffer;
>
> Method 2:
> char *buffer = operator new (BUFSIZE);
> operator delete (buffer);
>
> Method 3:
> char *buffer = malloc (BUFSIZE);
> free (buffer);
>
> Which is the most efficient / most appropriate ?
>
With a decent implementation, there should be little difference if
any, between 1 and 2. Method 3 tends to be discouraged in C++,
but is not fundamentally incorrect.
My opinion of most "appropriate" is method 1, as that is the more
usual method of dynamically allocating an array of char in C++.
With performance between the choices, YMMV. If that sort of
thing is critical, you will need to test for your compiler
and likely deployment environments.
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Francis Glassborow
writes
>Which is the best and most efficient way to allocate and free large
>amounts of raw memory in C++, e.g. for a graphics buffer.
>
>Lets say I want to allocate/free a char array. I know three ways how to
>do that:
>
>Method 1:
> char *buffer = new char[BUFSIZE];
> delete[] buffer;
>
>Method 2:
> char *buffer = operator new (BUFSIZE);
> operator delete (buffer);
>
>Method 3:
> char *buffer = malloc (BUFSIZE);
> free (buffer);
>
>
>Which is the most efficient / most appropriate ?
It all depends on context. Personally 1) would be my default and 3 my
choice if I thought that the standard version of new[]/delete[] might be
replaced and I definitely did not want support for such extras as
garbage collecting allocators.
Francis Glassborow Association of C & C++ Users
64 Southfield Rd
Oxford OX4 1PA +44(0)1865 246490
All opinions are mine and do not represent those of any organisation
Martin Fabian
>
<snip>
> Method 2:
> char *buffer = operator new (BUFSIZE);
> operator delete (buffer);
>
This needs a cast, not?
A value of type void * cannot be used to initialize an entity of type
char *.
<snap>
--
Martin Fabian http://www.s2.chalmers.se/~fabian/
--
"Cheer up. It may never happen" (Edina Monsoon)
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Ian Bruntlett
"Ernst K. Locker" <ern...@usa.net> wrote in message
news:8p6b0...@e42ilheb.net...
> Which is the best and most efficient way to allocate and free
> large amounts of raw memory in C++, e.g. for a graphics buffer.
It depends on your C++ compiler and its implementation of new/delete and
malloc.
If you're doing C++, I'd use method 1. I'm no language lawyer but method 2
seems to be another way of doing method 1.
I don't know what you're writing but I might end up writing something like:
class GraphicsBuffer
{
// stuff I want to do with graphics
};
// later on
GraphicsBuffer * pGraphicsBuffer = new GraphicsBuffer;
pGraphicsBuffer -> Blah();
delete pGraphicsBuffer;
Ian
> Lets say I want to allocate/free a char array. I know three ways
> how to do that:
>
> Method 1:
> char *buffer = new char[BUFSIZE];
> delete[] buffer;
>
> Method 2:
> char *buffer = operator new (BUFSIZE);
> operator delete (buffer);
>
> Method 3:
> char *buffer = malloc (BUFSIZE);
> free (buffer);
>
>
> Which is the most efficient / most appropriate ?
[ Send an empty e-mail to c++-...@netlab.cs.rpi.edu for info ]
Steve Molitor
> Method 1 allocates an array of a type and would normally call the constructor
> for each array element, but not for simple builtin types like char.
>
> Whereas Method 2 allocates raw memory of type void*.
So, what's the difference? new char[SIZE] won't call the constructor,
neither will the more complicated second example.
--
Steve Molitor
smol...@erac.com
Matt Osborn
>
> ern...@usa.net (Ernst K. Locker) writes:
>
> > Method 1 allocates an array of a type and would normally call the
constructor
> > for each array element, but not for simple builtin types like char.
> >
> > Whereas Method 2 allocates raw memory of type void*.
>
> So, what's the difference? new char[SIZE] won't call the constructor,
> neither will the more complicated second example.
>
Curious about this. Would method 2 allow an array to be correctly
handled by an auto ptr?
Luis Coelho
>"Ian Bruntlett" <Ian.Br...@nospam.thank.you> wrote:
>>
>>"Ernst K. Locker" <ern...@usa.net> wrote in message
>>news:8p6b0...@e42ilheb.net...
>>> Which is the best and most efficient way to allocate and free
>>> large amounts of raw memory in C++, e.g. for a graphics buffer.
>>
>>It depends on your C++ compiler and its implementation of new/delete and
>>malloc.
>>
>>> char *buffer = new char[BUFSIZE];
>>> delete[] buffer;
>>>
>>> Method 2:
>>>::operator delete (buffer);
>
>>If you're doing C++, I'd use method 1. I'm no language lawyer but method
2
>>seems to be another way of doing method 1.
>
>
>Method 1 allocates an array of a type and would normally call the
constructor
>for each array element, but not for simple builtin types like char.
>
>Whereas Method 2 allocates raw memory of type void*.
I'm really not sure, but I think there could be alignment issues with
solution
1. The memory is aligned for char[] which normally can be anywhere. In
method 2
you are garanteed memory which is aligned for everything.
Anothe reason I'd prefer method 2 is that I find it more explicit. It is
visible that it is raw storage you're after.
Regards
--
Luis Pedro Coelho.
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