C++ code with C-style interface for a library to be used in C++ and C?

[Koen]

Hi!

I have a question about building and then using libraries containing
C++ code.

Let's say I have some C++ code and a .cpp file with 1 function that
uses some other C++ code / classes etc... Also, any possible exception
is handled within the function itself.

In code:

MyModule.h
----------
#ifndef MYMODULE_H
#define MYMODULE_H

extern int Test(float inParam1,float inParam2,float* outResult);

#endif // #ifndef MYMODULE_H

MyModule.cpp
------------
#include "MyModule.h"
#include "MyClasses.h" // contains MyClassA and MyClassB

int Test(float inParam1,float inParam2,float* outResult)
{
int theResult = 0;
try
{
MyClassA a;
a.Setup(inParam1);
MyClassB b;
b.Setup(inParam2);
*outResult = a.Process(b);
}
catch (...)
{
theResult = -1;
}
return theResult;
}

Now, I would like to build a library that is callable from C++ AND
from C that exposes the functionality of that Test function (I just
gave an example with 1 single function, but in practice there are
more).

Currently, when I build the library, it is compiled using the C++
compiler (of course, since I really use C++ classes and so on), and I
can use the library from a C++ program (.cpp file with main), as
should...

But I can't seem to find out how to make that function accessible to a
C program (.c file with main). I get an error like "unresolved
external symbol _Test", and I know that it probably has something to
do with the name mangling in C++ being different from C...
Considering the fact that the *interface* of the library does not
contain any C++ specific things, and handles all possible exceptions
internally, it should be possible to use it in C too, right?

Can someone please explain me how to do that?
Thanks in advance!

Koen

PS
If someone wants the test code, I can post/send them on request.

[Koen]

"Koen" <[e-mail]> wrote in message
news:bk**********@gaudi2.UGent.be...

Hi!

I have a question about building and then using libraries containing
C++ code.

Let's say I have some C++ code and a .cpp file with 1 function that
uses some other C++ code / classes etc... Also, any possible exception is handled within the function itself.

In code:

MyModule.h
----------
#ifndef MYMODULE_H
#define MYMODULE_H

extern int Test(float inParam1,float inParam2,float* outResult);

#endif // #ifndef MYMODULE_H

OK. Seems like all I needed to do was this:

#ifndef MYMODULE_H
#define MYMODULE_H

#ifdef __cplusplus
extern "C" {
#endif

int Test(float inParam1,float inParam2,float* outResult);

#ifdef __cplusplus
}
#endif

#endif // #ifndef MYMODULE_H
Only thing I'm not sure of anymore is whether I should still keep the
"extern" in front of my function (so that also in the C case there is
an "extern"):

extern int Test(float inParam1,float inParam2,float* outResult);

Does that still have any use?

Koen

[Julián Albo]

Koen escribió:

But I can't seem to find out how to make that function accessible to a
C program (.c file with main). I get an error like "unresolved
external symbol _Test", and I know that it probably has something to
do with the name mangling in C++ being different from C...

Declare your function as extern "C".

Regards.

[Mike Wahler]

"Koen" <[e-mail]> wrote in message
news:bk**********@gaudi2.UGent.be...

"Koen" <[e-mail]> wrote in message
news:bk**********@gaudi2.UGent.be...

Hi!

I have a question about building and then using libraries containing
C++ code.

Let's say I have some C++ code and a .cpp file with 1 function that
uses some other C++ code / classes etc... Also, any possible exception

is handled within the function itself.

In code:

MyModule.h
----------
#ifndef MYMODULE_H
#define MYMODULE_H

extern int Test(float inParam1,float inParam2,float* outResult);

#endif // #ifndef MYMODULE_H

OK. Seems like all I needed to do was this:

#ifndef MYMODULE_H
#define MYMODULE_H

#ifdef __cplusplus
extern "C" {
#endif

int Test(float inParam1,float inParam2,float* outResult);

#ifdef __cplusplus
}
#endif

#endif // #ifndef MYMODULE_H
Only thing I'm not sure of anymore is whether I should still keep the
"extern" in front of my function (so that also in the C case there is
an "extern"):

extern int Test(float inParam1,float inParam2,float* outResult);

In both C and C++, functions are 'extern' by default,
and need not be qualified as such.

The use of 'extern' with 'extern "C"' has a special
purpose meaning, used for the interlanguage interface.

Does that still have any use?

No, it never did. :-)

-Mike

[Koen]

"Mike Wahler" <mk******@mkwahler.net> wrote in message
news:fh*****************@newsread3.news.pas.earthl ink.net...

In both C and C++, functions are 'extern' by default,
and need not be qualified as such.

The use of 'extern' with 'extern "C"' has a special
purpose meaning, used for the interlanguage interface.

Does that still have any use?

No, it never did. :-)

OK. Thanks for the info!
Koen

[Jack Klein]

On Fri, 19 Sep 2003 15:49:33 +0200, "Koen" <[e-mail]> wrote in
comp.lang.c++:

Hi!

I have a question about building and then using libraries containing
C++ code.

Let's say I have some C++ code and a .cpp file with 1 function that
uses some other C++ code / classes etc... Also, any possible exception
is handled within the function itself.

In code:

MyModule.h
----------
#ifndef MYMODULE_H
#define MYMODULE_H

extern int Test(float inParam1,float inParam2,float* outResult);

#endif // #ifndef MYMODULE_H

MyModule.cpp
------------
#include "MyModule.h"
#include "MyClasses.h" // contains MyClassA and MyClassB

int Test(float inParam1,float inParam2,float* outResult)
{
int theResult = 0;
try
{
MyClassA a;
a.Setup(inParam1);
MyClassB b;
b.Setup(inParam2);
*outResult = a.Process(b);
}
catch (...)
{
theResult = -1;
}
return theResult;
}

Now, I would like to build a library that is callable from C++ AND
from C that exposes the functionality of that Test function (I just
gave an example with 1 single function, but in practice there are
more).

Currently, when I build the library, it is compiled using the C++
compiler (of course, since I really use C++ classes and so on), and I
can use the library from a C++ program (.cpp file with main), as
should...

But I can't seem to find out how to make that function accessible to a
C program (.c file with main). I get an error like "unresolved
external symbol _Test", and I know that it probably has something to
do with the name mangling in C++ being different from C...
Considering the fact that the *interface* of the library does not
contain any C++ specific things, and handles all possible exceptions
internally, it should be possible to use it in C too, right?

Can someone please explain me how to do that?
Thanks in advance!

Koen

PS
If someone wants the test code, I can post/send them on request.

You probably can't use C++ code that does things like throwing and
catching exceptions from inside a C program.

While this is implementation specific, it is often necessary on many
platforms for a program containing mixed C and C++ object modules to
have the start-up and main() in C++. It is quite possible that the C
environment created by the C compiler for a C executable will not have
appropriate support for C++ only features such as exceptions.

--
Jack Klein
Home: http://JK-Technology.Com
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