Using C++ functions from C

[MSG]

Hello

The C++ standard provides a way to access C function, which is `extern
"C"`, however, what about the compatibility in the opposite direction?

If my C++ function happens to have the signature of a valid C
function, are there guarantees about its usability from C?

Thanks
MSG

[DeMarcus]

Re: Using C++ functions from C



MSG wrote:[color=blue]
> Hello
>
> The C++ standard provides a way to access C function, which is `extern
> "C"`, however, what about the compatibility in the opposite direction?
>
> If my C++ function happens to have the signature of a valid C
> function, are there guarantees about its usability from C?
>
> Thanks
> MSG[/color]

I haven't investigated it thoroughly, but try enclose your C++ functions
within extern "C" {} as well. Of course it has to be static functions,
but they in turn can use C++ fully.

Regards
Daniel Marcus

[David Harmon]

Re: Using C++ functions from C

On 9 Feb 2004 02:48:31 -0800 in comp.lang.c++, msg1825@yahoo.c om (MSG)
was alleged to have written:[color=blue]
>The C++ standard provides a way to access C function, which is `extern
>"C"`, however, what about the compatibility in the opposite direction?
>
>If my C++ function happens to have the signature of a valid C
>function, are there guarantees about its usability from C?[/color]

Not "just happens to" but you have declared it have "C" linkage with
extern "C"

This issue is covered in Marshall Cline's C++ FAQ. See the topic
"[32.6] How can I create a C++ function f(int,char,floa t) that is
callable by my C code?" It is always good to check the FAQ before
posting. You can get the FAQ at:

http://www.parashift.com/c++-faq-lite/

[Evan Carew]

Re: Using C++ functions from C

MSG,

If you need an example project which accomplishes this task, drop me a line.

Evan Carew

MSG wrote:[color=blue]
> Hello
>
> The C++ standard provides a way to access C function, which is `extern
> "C"`, however, what about the compatibility in the opposite direction?
>
> If my C++ function happens to have the signature of a valid C
> function, are there guarantees about its usability from C?
>
> Thanks
> MSG[/color]

[Dylan Nicholson]

Re: Using C++ functions from C

DeMarcus <nobody@tellus. orb> wrote in message news:<40277462. 4070208@tellus. orb>...[color=blue]
> MSG wrote:[color=green]
> > Hello
> >
> > The C++ standard provides a way to access C function, which is `extern
> > "C"`, however, what about the compatibility in the opposite direction?
> >
> > If my C++ function happens to have the signature of a valid C
> > function, are there guarantees about its usability from C?
> >
> > Thanks
> > MSG[/color]
>
> I haven't investigated it thoroughly, but try enclose your C++ functions
> within extern "C" {} as well. Of course it has to be static functions,
> but they in turn can use C++ fully.
>[/color]

Hmm...I'm unsure as to the exact meaning of extern "C" { static void
foo(); } - you're telling the compiler two things at once (firstly
that you want it to have external "C"-style linkage, secondly that you
want it not to be visible outside the current compilation unit). Note
that extern "C" is not valid on a struct/class member, even if it is
'static'. And

extern "C" static void foo();

is not a valid declaration.

Dylan

[DeMarcus]

Re: Using C++ functions from C



Dylan Nicholson wrote:
[color=blue]
> DeMarcus <nobody@tellus. orb> wrote in message news:<40277462. 4070208@tellus. orb>...
>[color=green]
>>MSG wrote:
>>[color=darkred]
>>>Hello
>>>
>>>The C++ standard provides a way to access C function, which is `extern
>>>"C"`, however, what about the compatibility in the opposite direction?
>>>
>>>If my C++ function happens to have the signature of a valid C
>>>function, are there guarantees about its usability from C?
>>>
>>>Thanks
>>>MSG[/color]
>>
>>I haven't investigated it thoroughly, but try enclose your C++ functions
>>within extern "C" {} as well. Of course it has to be static functions,
>>but they in turn can use C++ fully.
>>[/color]
>
>
> Hmm...I'm unsure as to the exact meaning of extern "C" { static void
> foo(); } - you're telling the compiler two things at once (firstly
> that you want it to have external "C"-style linkage, secondly that you
> want it not to be visible outside the current compilation unit). Note
> that extern "C" is not valid on a struct/class member, even if it is
> 'static'. And
>
> extern "C" static void foo();
>
> is not a valid declaration.
>
> Dylan[/color]


I made a small program like this

class MyCppClass
{
public:
char* helloWorldMessa ge( void ) { return "Hello World"; }
};

extern "C"
{

char* foo( void )
{
MyCppClass cpp;

return cpp.helloWorldM essage();
}

}

It seems to work, but I'm curious in what the common way
to solve this task is.

Daniel

[EventHelix.com]

Re: Using C++ functions from C

You cannot do that as a C++ method maps to a C function with an additional
pointer that points to the object.

See the following article for details:

http://www.eventhelix.com/RealtimeMantra/Basics/ComparingCPPAndCPerformance.htm

Sandeep
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