memcpy equivalent in C++

Hi,
I would like to know if C++ has a class equivalent to
memcpy and its associated functions available in C.

re: memcpy equivalent in C++

On Nov 19, 9:11*am, mthread <rjk...@gmail.comwrote:
It is std::copy() from <algorithmheader. http://www.sgi.com/tech/stl/copy..html

--
Max

re: memcpy equivalent in C++

On 2008-11-19 10:11, mthread wrote:memcpy() is also available in C++, but you should only use it for raw
data, if you use it on objects you might get nasty surprises. For
objects you should use std::copy() as Max pointed out.

--
Erik Wikström

re: memcpy equivalent in C++

Maxim Yegorushkin wrote:std::copy is not the same thing as memcpy. std::copy honors C++
objects' copy semantics, which can be a lot more complicated than what
memcpy supports. The OP probably wants std::memcpy, from the <cstring>
header.

I wonder whether popular implementations of std::copy delegate to memcpy
for types with trivial copy constructors.

re: memcpy equivalent in C++

On 2008-11-19 14:26:34 -0500, Jeff Schwab <jeff@schwabcenter.comsaid:
Yes, they do.

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

re: memcpy equivalent in C++

On Nov 19, 8:26 pm, Jeff Schwab <j...@schwabcenter.comwrote:They may or they may not. With a good compiler, generating the
code directly inline probably results in faster code, and maybe
even smaller code.

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James Kanze (GABI Software) email:james.kanze@gmail.com
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re: memcpy equivalent in C++

Erik Wikström wrote:If a class has only basic types (and possible arrays of basic types)
as members and only has the default compiler-generated copy constructor
and assignment operator, is the behavior of copying objects of that
class with memcpy() still undefined?

re: memcpy equivalent in C++

James Kanze wrote:That raises another interesting question: Are there any platforms that
define both their C and C++ standard libraries on top of a shared
subset, rather than just providing C++ aliases for old C? For example,
are there any implementations that just forward both memcpy and
(sometimes) std::copy to an internal __inline_memcpy?

re: memcpy equivalent in C++

Juha Nieminen wrote:That depends what you consider "basic types." If the types involved are
POD, the behavior is defined (as long as neither of the objects is a
sub-object of the other). See 3.9 Types [basic.types], paragraph 3.

re: memcpy equivalent in C++

Jeff Schwab wrote:Yes. For example one produced by a big company that also does OSs and
office packages.

Not only will memcpy be inlined by the compiler, but a for loop in
user code will also be optimized into identical machine code.


Using memcpy is NOT a magical optimization trick!


Bo Persson

re: memcpy equivalent in C++

On Nov 20, 2:03 pm, Jeff Schwab <j...@schwabcenter.comwrote:There are probably some, but in many cases, the C library is
bundled with the system.
I always thought that the usual implementation of memcpy in the
C header was something like:

extern void* memcpy( void* dest, void const* src, size_t n ) ;
#define memcpy( dest, src, n ) __builtin_memcpy( dest, src, n )

(But of course, this causes problems when the library is bundled
as well.) And of course, since it is a template, the compiler
can already see all of the code for std::copy, and optimize
accordingly.

Of course, this is only valid for simple functions like memcpy.
I can't imagine any implementation using a compiler builtin for
something like strftime.

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James Kanze (GABI Software) email:james.kanze@gmail.com
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re: memcpy equivalent in C++

On Nov 20, 2:02 pm, Juha Nieminen <nos...@thanks.invalidwrote:If the class is a POD struct or a POD union, the behavior is
well defined. If the class contains pointers, it may not be
what you want, but it is well defined.

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James Kanze (GABI Software) email:james.kanze@gmail.com
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