Re: extern "C"

From:

Abhishek Padmanabh <abhishek.padmanabh@gmail.com>

Newsgroups:

microsoft.public.vc.language

Date:

Sat, 9 Feb 2008 11:32:04 -0800 (PST)

Message-ID:

<d3caf439-b3e8-422a-ba46-2ac238ef18c9@z17g2000hsg.googlegroups.com>

On Feb 10, 12:29 am, Abhishek Padmanabh <abhishek.padman...@gmail.com>
wrote:

On Feb 9, 2:08 pm, George <Geo...@discussions.microsoft.com> wrote:

Thanks Drew!

Compiler/Linker will error if linkage specifications don't match.

What is your context about the one-sentence statement? You mean you pref=

to add extern "C" to both declaration and definition?

regards,
George

"Drew" wrote:

Compiler/Linker will error if linkage specifications don't match.

Drew

"George" <Geo...@discussions.microsoft.com> wrote in message
news:D8810866-D9BC-4B78-AF05-BE63C777410F@microsoft.com...

Thanks for your advice, Ben!

BTW: to make it safe, we should add extern "C" to both declaration a=

definition, right?

regards,
George

"Ben Voigt [C++ MVP]" wrote:

Tim Roberts wrote:

George <Geo...@discussions.microsoft.com> wrote:

Just to confirm what is the most correct way beyond a just worki=

function.

1.

We need to add extern "C" to both variable/function
definition/declaration? Or only need to add to the variable/func=

tion

declaration?

2.

How about extern? Declaration only or both declaration and
definition are required?

BTW: previously, I only add to declaration, but after reading mo=

and more code which add to both declaration and definition, I co=

to here to ask this question.

extern "C" is only required for the declaration.

Do you understand that extern "C" is only used for C++ that you n=

eed

to call from a C function?

extern "C" should also be used with dllexport, even if the caller i=

s C++,

to
get rid of the (compiler version dependent) name mangling.- Hide qu=

oted text -

- Show quoted text -

extern "C" specifies external linkage spec for the functions that you
declare somewhere. If these functions are just used in one compilation
unit, giving in extern "C" or not probably does not matter. It is only
when you use those functions somewhere else (in some other .cpp/.c
file). Usually, you would not copy the full implementation of that
function everywhere. You would have a header file and you keep
including that in the other compilation units. And you would include
that header (with function declarations) in the file that implements
them. So, the compiler is able to see that the function has already
been declared as extern "C", and hence you don't need to put it with
the function definitions. There can be special cases, for example -
the one mentioned by Ben Voigt above regarding putting extern "C" to
dll exported functions.

.. that is there can be cases where you don't have a function
declaration (prototype not defined) in that case, you would be forced
to put it into the function definitions.