How to call a C++ function from c code?

**CBFalconer** · Aug 3 '08, 03:15 AM

Re: How to call a C++ function from c code?

"AL@TW" wrote:

>
How to call a C++ function from c code?
extern "C++"?

No. In general, you can't, because of C++ overloading. You can
call C from C++, however.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

**Stephen Sprunk** · Aug 3 '08, 03:15 AM

Re: How to call a C++ function from c code?

AL@TW wrote:

How to call a C++ function from c code?
extern "C++"?
>
I think it just inhibit the warning.
I maybe have to consider c++ object creation problem.

This is OT for comp.lang.c; comp.lang.c++ is down the hall, to the left.

<OT>
The answer I assume you'll get is that the C++ function declaration
should be enclosed in an extern "C" { ... } block when compiled in C++,
while the prototype declaration that the C compiler sees should _not_ be
so enclosed. The usual way to do this is with the BEGIN_C_DECLS and
END_C_DECLS macros (Google for the idiomatic definitions) in a single
header that can be used by compilers of both languages.

I don't recall if the C++ compiler needs the function definition to be
enclosed with extern "C" { ... } or whether it will "remember" to
compile the function C-style simply by having the declaration enclosed.

Does the C++ need to be a static function?

No. However, some features of C++ aren't available in a function that
is being compiled as extern "C", like default arguments, variable
signatures, etc. I'm pretty sure there's no way to do it with a class
method either, whether static or not, just plain functions. A common
tactic is to have a C-compatible "wrapper" function, which in turn calls
the real C++ functions. (For instance, an object may be passed in to
the wrapper via a void* parameter, and the wrapper then casts it to an
object and invokes a method on the result.)
</OT>

BTW, the c code is compiled with C++ compiler.

If you're compiling it with a C++ compiler, the code is C++. You may
have used a subset of C++ that looks the same as C (and hopefully has
the same meaning, which isn't guaranteed), but it isn't C unless you're
using a C compiler.

S

**Peter Nilsson** · Aug 3 '08, 03:25 AM

Re: How to call a C++ function from c code?

"AL@TW" <schosnab...@gm ail.comwrote:

How to call a C++ function from c code?

You don't. [You can in certain cases, but the details
are implementation specific and outside the scope of
the C language itself, hence off-topic in comp.lang.c.]

extern "C++"?
I think it just inhibit the warning.
I maybe have to consider c++ object creation problem.
>
Does the C++ need to be a static function?

Ask about C++ in comp.lang.c++.

BTW, the c code is compiled with C++ compiler.

Then you don't have a C language question, but a C++
question. Again, ask in comp.lang.c++.

--
Peter

**Keith Thompson** · Aug 3 '08, 04:45 AM

Re: How to call a C++ function from c code?

CBFalconer <cbfalconer@yah oo.comwrites:

"AL@TW" wrote:

>How to call a C++ function from c code?
>extern "C++"?

>
No. In general, you can't, because of C++ overloading. You can
call C from C++, however.

<OT>
Yes, you can call C from C++, and you can call C++
from C. This is explained in the "C++ FAQ Lite",
<http://www.parashift.c om/c++-faq-lite/>, section 32.

Chuck, as I recall, last time we discussed this, you refused to
believe it was possible to call C++ from C even after I demonstrated
it.

In any case, it happens to be C++, not C, that provides the
mechanisms for calling functions in either language from the other,
so this is a question a comp.lang.c++ -- but only if the C++ FAQ
doesn't answer the question.

But as Stephen Sprunk already pointed out, the OP isn't really trying
to call C++ from C anyway; since he's compiling all is code with
a C++ compiler, it's all C++ code, and there are no inter-language
calling issues at all. (What the OP is already doing may well be
the best approach anyway.)
</OT>

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

**Ian Collins** · Aug 3 '08, 05:25 AM

Re: How to call a C++ function from c code?

CBFalconer wrote:

"AL@TW" wrote:

>How to call a C++ function from c code?
>extern "C++"?

>
No. In general, you can't, because of C++ overloading.

Not that old nonsense again. I though we ponded the truth into you last
time around.

--
Ian Collins.

**Richard Heathfield** · Aug 3 '08, 05:55 AM

Re: How to call a C++ function from c code?

Ian Collins said:

CBFalconer wrote:

>"AL@TW" wrote:

>>How to call a C++ function from c code?
>>extern "C++"?

>>
>No. In general, you can't, because of C++ overloading.

>
Not that old nonsense again. I though we ponded the truth into you last
time around.

<croak>
Ribbit. Ribbit.
</croak>

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

**Ian Collins** · Aug 3 '08, 06:05 AM

Re: How to call a C++ function from c code?

Richard Heathfield wrote:

Ian Collins said:
>

>CBFalconer wrote:

>>"AL@TW" wrote:
>>>How to call a C++ function from c code?
>>>extern "C++"?
>>No. In general, you can't, because of C++ overloading.

>Not that old nonsense again. I though we ponded the truth into you last
>time around.

>
<croak>
Ribbit. Ribbit.
</croak>
>

:)

--
Ian Collins.

**Malcolm McLean** · Aug 3 '08, 09:05 AM

Re: How to call a C++ function from c code?

"AL@TW" <schosnablue@gm ail.comwrote in message

How to call a C++ function from c code?
extern "C++"?
>

Three ways:

1) extern "C" the C++ function in C++ code. If you don't want to touch the
C++ source, write a wrapper.

2) Compile the C code under C++ and call in the normal way. Note this means
you'll have to be careful not to use any C-only constructs, like uncast
malloc().

3) Examine the object file that the C++ compiler creates and call the
mangled function names that it outputs. This is the worst option but
cometimes necessary.

--
Free games and programming goodies.

http://www.personal.leeds.ac.uk/~bgy1mm

**CBFalconer** · Aug 3 '08, 10:15 AM

Re: How to call a C++ function from c code?

Ian Collins wrote:

CBFalconer wrote:

>"AL@TW" wrote:
>>

>>How to call a C++ function from c code?
>>extern "C++"?

>>
>No. In general, you can't, because of C++ overloading.

^^^^^^^^^^^

>
Not that old nonsense again. I though we ponded the truth into
you last time around.

And I cavilled above.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

**Greg Comeau** · Aug 3 '08, 05:45 PM

Re: How to call a C++ function from c code?

In article <910db35a-ad6e-481b-8203-fc70d5102e5c@a3 g2000prm.google groups.com>,
AL@TW <schosnablue@gm ail.comwrote:

>How to call a C++ function from c code?
>extern "C++"?
>
>I think it just inhibit the warning.
>I maybe have to consider c++ object creation problem.
>
>Does the C++ need to be a static function?
>
>BTW, the c code is compiled with C++ compiler.

Check out http://www.comeaucomputing.com/techtalk/#externc
--
Greg Comeau / 4.3.10.1 with C++0xisms now in beta!
Comeau C/C++ ONLINE == http://www.comeaucomputing.com/tryitout
World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90.
Comeau C/C++ with Dinkumware's Libraries... Have you tried it?

**Keith Thompson** · Aug 3 '08, 06:25 PM

Re: How to call a C++ function from c code?

CBFalconer <cbfalconer@yah oo.comwrites:

Ian Collins wrote:

>CBFalconer wrote:

>>"AL@TW" wrote:
>>>
>>>How to call a C++ function from c code?
>>>extern "C++"?
>>>
>>No. In general, you can't, because of C++ overloading.

^^^^^^^^^^^

>>
>Not that old nonsense again. I though we ponded the truth into
>you last time around.

>
And I cavilled above.

The problem is that the phrase "In general" is ambiguous here. I
think what you meant is that it's not always possible, which is true.
An equally reasonable reading is that it's *usually* not possible,
which is not true. (Even in the presence of overloading, you can
provide a uniquely named C++ wrapper.)

In any case, saying that "In general, you can't" is hardly responsive
to a question about how to do it.

Yes, you certainly can call C++ from C. No, you can't always do it;
there are cases where C++ features are incompatible with C, making a
C-to-C++ call impossible or impractical. Since it happens to be C++,
not C, that provides the mechanisms for cross-language calls in both
directions, comp.lang.c++ is the place to ask about it, but only if
the detailed information in the "C++ FAQ Lite" doesn't already answer
the question.

Yes, this is off-topic, but (a) I'm providing a redirection to a forum
where it's topical, and (b) I'm also correcting a statement that's
both off-topic and misleading.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

**Kenny McCormack** · Aug 4 '08, 02:05 PM

Re: How to call a C++ function from c code?

In article <lnabfuc65e.fsf @nuthaus.mib.or g>,
Keith Thompson <kst-u@mib.orgwrote:

>CBFalconer <cbfalconer@yah oo.comwrites:

>Ian Collins wrote:

>>CBFalconer wrote:
>>>"AL@TW" wrote:
>>>>
>>>>How to call a C++ function from c code?
>>>>extern "C++"?
>>>>
>>>No. In general, you can't, because of C++ overloading.

> ^^^^^^^^^^^

>>>
>>Not that old nonsense again. I though we ponded the truth into
>>you last time around.

>>
>And I cavilled above.

>
>The problem is that the phrase "In general" is ambiguous here. I

But you of all people should know that Chuck's interpretation *is* the
clc-approved one. People routinly say things like "That doesn't work in
general" when it works perfectly well on 99.9999% of all known machines.

And, mathematically speaking, they are right (to do so).

How to call a C++ function from c code?

How to call a C++ function from c code?

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