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Calling C++ from C

I'm trying to write some C++ library routines callable by C.
The functions are declared extern "C" but I'm getting the
loader complaining it can't resolve new() and delete(). Am I
just missing a library or is the C++ runtime environment
also an issue? Compiling the C program as a C++ program
seems to work but I'd rather have the library look like
a plain C library.

Joe Seigh
Jul 22 '05
12 1845
On Thu, 20 Jan 2005 14:28:42 +0100, Karl Heinz Buchegger <kb******@gasca d.at> wrote:
Joseph Seigh wrote:

On Wed, 19 Jan 2005 21:17:46 -0500, Victor Bazarov <v.********@com Acast.net> wrote:
> Let me get this straight. The library has a C interface. But it'll
> be impossible to use from C due to the same problem you yourself
> encountered (missing libraries when linking). So, it will only be
> useful within a C++ project/program. Why not do the users of it
> a favour and leave it C++?

So the library can have wider application.

But it can't.
There is no way around it. If it is implemented in C++, then the user
of your library has no other choice then to link the C++ runtime in,
even if he is programming in C.
Here is the deal: What if I have a C compiler only? Then you sold
me a library which is useless for me because I cannot link to it
because of the missing C++ runtime library. So it turns out that
I need to by the C++ compiler (from the same vendor and hopefully
their C library and C++ library are compatible) also, just in order
to link to your library. But then: what is hindering me to use the
C++ compiler in the first place? But then the next question is:
If I am limited to C++ anyway, why did you restrict yourself to
a C API only?

See. When using C++ as implementation language with a C style
interface you have gained nothing et all. I am still forced
to use a C++ compiler.

You're missing the point. The bulk of the applications that would
use the api are written in C. If I restrict the api to C++, I lose
most of those applications since most multi-threading applications
are written in C.

The stuff I'm planning to do is here

subject to change. I'll have to seriously consider rewriting atomic_ptr
in C. It'd be a lot more awkard to use but it might be worth it to
avoid C++ controversy.

Joe Seigh
Jul 22 '05 #11
Joseph Seigh wrote:
I'm trying to write some C++ library routines callable by C.
The functions are declared extern "C" but I'm getting the
loader complaining it can't resolve new() and delete(). Am I
just missing a library or is the C++ runtime environment
also an issue? Compiling the C program as a C++ program
seems to work but I'd rather have the library look like
a plain C library.

If you're compiling C++, you'll have to include the C++ Standard
at some point. Now, you're getting close to off-topic because
you're building something without a main(), but anyway: when
compiling a DLL you end up with two link steps. If you can't
include the C++ lib in the second (dynamic) link fase, you
must link it in the first (static) link fase.

Of course, no guarantees yet, libraries are not yet in ISO C++,
and mixed-lang programming is always implementation-defined.
Michiel Salters

Jul 22 '05 #12
> I'm trying to write some C++ library routines callable by C.
The functions are declared extern "C" but I'm getting the
loader complaining it can't resolve new() and delete(). Am I
just missing a library or is the C++ runtime environment
also an issue? Compiling the C program as a C++ program
seems to work but I'd rather have the library look like
a plain C library.

Would you like to apply the techniques that are described by Matthew Wilson in the
sections "7.4 I Can C Clearly Now" and "7.4.4 Getting a Handle on C++ Classes" of the book
"Imperfect C++" (ISBN 0-321-22877-4) for your evolving library?

Jul 23 '05 #13

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