C++ library access from C

[TBass]

Hi,

This is going to be one of those annoyingly stupid questions.

I would like to compile a library as a C++ program, but it needs to be
able to work with a C program as well. I only want to distribute one
..lib file and an H file.

I know that I can call a C library from a C++ program. Is it possible
to compile a CPP library that can be called from a C program?

For the, "why not just make it a C library and stop wasting our time?"
question, I need to handle some OLE/OCP calls, and I'm trying to avoid
the pain the arse of doing OLE in C.

Thanks in advance,
Tom

[Victor Bazarov]

Re: C++ library access from C

TBass wrote:

This is going to be one of those annoyingly stupid questions.
>
I would like to compile a library as a C++ program, but it needs to be
able to work with a C program as well. I only want to distribute one
.lib file and an H file.
>
I know that I can call a C library from a C++ program. Is it possible
to compile a CPP library that can be called from a C program?

Yes, what you usually do is provide a C interface for every C++ function
you expect to call:

int my_Cpp_function (const char*);

extern "C" int my_Cpp_function _C_wrapper(cons t char* cptr) {
return my_Cpp_function (cptr);
}

Of course, it means that no C++ types can be present in the interface.

For the, "why not just make it a C library and stop wasting our time?"
question, I need to handle some OLE/OCP calls, and I'm trying to avoid
the pain the arse of doing OLE in C.

Agreed.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[TBass]

Re: C++ library access from C

[snip]

Yes, what you usually do is provide a C interface for every C++ function
you expect to call:
>
int my_Cpp_function (const char*);
>
extern "C" int my_Cpp_function _C_wrapper(cons t char* cptr) {
return my_Cpp_function (cptr);
}
>
Of course, it means that no C++ types can be present in the interface.

[/snip]

There aren't any. Thanks! That's a big help.

[Roland Pibinger]

Re: C++ library access from C

On Fri, 29 Sep 2006 12:50:58 -0400, "Victor Bazarov"
<v.Abazarov@com Acast.netwrote:

>TBass wrote:

>This is going to be one of those annoyingly stupid questions.
>I would like to compile a library as a C++ program, but it needs to be
>able to work with a C program as well. I only want to distribute one
>.lib file and an H file.

>
>Yes, what you usually do is provide a C interface for every C++ function
>you expect to call:
>
int my_Cpp_function (const char*);
>
extern "C" int my_Cpp_function _C_wrapper(cons t char* cptr) {
return my_Cpp_function (cptr);
}
>
>Of course, it means that no C++ types can be present in the interface.

You can use forward declared C++ types - 'class' renamed to 'struct'
which may be helpful in that case.

Best regards,
Roland Pibinger

[Greg Comeau]

Re: C++ library access from C

In article <1159548059.941 307.147180@e3g2 000cwe.googlegr oups.com>,
TBass <tbj@automatedd esign.comwrote:

>I would like to compile a library as a C++ program, but it needs to be
>able to work with a C program as well. I only want to distribute one
>.lib file and an H file.
>
>I know that I can call a C library from a C++ program. Is it possible
>to compile a CPP library that can be called from a C program?
>
>For the, "why not just make it a C library and stop wasting our time?"
>question, I need to handle some OLE/OCP calls, and I'm trying to avoid
>the pain the arse of doing OLE in C.

Check out http://www.comeaucomputing.com/techtalk/#externC

If your library is a class library, or template library, etc.
for all practical purposes, don't do that.
--
Greg Comeau / 20 years of Comeauity! Intel Mac Port now in alpha!
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?

[Greg Comeau]

Re: C++ library access from C

In article <451d629c.11817 99@news.utanet. at>,
Roland Pibinger <rpbg123@yahoo. comwrote:

>On Fri, 29 Sep 2006 12:50:58 -0400, "Victor Bazarov"
><v.Abazarov@co mAcast.netwrote :

>>TBass wrote:

>>This is going to be one of those annoyingly stupid questions.
>>I would like to compile a library as a C++ program, but it needs to be
>>able to work with a C program as well. I only want to distribute one
>>.lib file and an H file.

>>
>>Yes, what you usually do is provide a C interface for every C++ function
>>you expect to call:
>>
> int my_Cpp_function (const char*);
>>
> extern "C" int my_Cpp_function _C_wrapper(cons t char* cptr) {
> return my_Cpp_function (cptr);
> }
>>
>>Of course, it means that no C++ types can be present in the interface.

>
>You can use forward declared C++ types - 'class' renamed to 'struct'
>which may be helpful in that case.

Only if it's truly POD classes.
--
Greg Comeau / 20 years of Comeauity! Intel Mac Port now in alpha!
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?

[Frederick Gotham]

Re: C++ library access from C

TBass posted:

I would like to compile a library as a C++ program, but it needs to be
able to work with a C program as well. I only want to distribute one
.lib file and an H file.
>
I know that I can call a C library from a C++ program. Is it possible
to compile a CPP library that can be called from a C program?

Here's a sample program:

/* defs.cpp */

extern "C" int Func(double const k) { return k / 3.2; }


/* header.h */

#ifdef __cplusplus
extern "C" int Func(double);
#else
int Func(double);
#endif

/* source1.c */

#include "header.h"

int main(void)
{
Func(53.6);
return 0;
}


/* source2.cpp */

#include "header.h"

int Abc()
{
Func(45.8);
return 0;
}

--

Frederick Gotham

[Roland Pibinger]

Re: C++ library access from C

On 29 Sep 2006 18:28:10 -0400, comeau@panix.co m (Greg Comeau) wrote:

>In article <451d629c.11817 99@news.utanet. at>,
>Roland Pibinger <rpbg123@yahoo. comwrote:

>>You can use forward declared C++ types - 'class' renamed to 'struct'
>>which may be helpful in that case.

>
>Only if it's truly POD classes.

When you use only pointers it works with non-POD classes too, eg.

// myclass.h

struct MyClass;
typedef struct MyClass MyClass;

extern "C" {
MyClass* createMyClass() ;
int doSomething (MyClass* m, int i);
void destroyMyClass (MyClass* m);
}


// myclass.cpp

#include "myclass.h"

class MyClass {
public:
virtual int doSomething (int i) { return i; }
virtual ~MyClass() {}
};


MyClass* createMyClass() { return new MyClass; }
int doSomething (MyClass* m, int i) {
return m ? m->doSomething( i) : 0;
}
void destroyMyClass (MyClass* m) { delete m; }


// usage in C program:

int main() {
MyClass* m = createMyClass() ;
doSomething (m, 7);
destroyMyClass (m);
}

Best regards,
Roland Pibinger

[Greg Comeau]

Re: C++ library access from C

In article <451e2505.26212 79@news.utanet. at>,
Roland Pibinger <rpbg123@yahoo. comwrote:

>On 29 Sep 2006 18:28:10 -0400, comeau@panix.co m (Greg Comeau) wrote:

>>In article <451d629c.11817 99@news.utanet. at>,
>>Roland Pibinger <rpbg123@yahoo. comwrote:

>>>You can use forward declared C++ types - 'class' renamed to 'struct'
>>>which may be helpful in that case.

>>
>>Only if it's truly POD classes.

>
>When you use only pointers it works with non-POD classes too, eg.
>
>// myclass.h
>
>struct MyClass;
>typedef struct MyClass MyClass;
>
>extern "C" {
MyClass* createMyClass() ;
int doSomething (MyClass* m, int i);
void destroyMyClass (MyClass* m);
>}
>
>
>// myclass.cpp
>
>#include "myclass.h"
>
>class MyClass {
>public:
virtual int doSomething (int i) { return i; }
virtual ~MyClass() {}
>};
>
>
>MyClass* createMyClass() { return new MyClass; }
>int doSomething (MyClass* m, int i) {
return m ? m->doSomething( i) : 0;
>}
>void destroyMyClass (MyClass* m) { delete m; }
>
>
>// usage in C program:
>
>int main() {
MyClass* m = createMyClass() ;
doSomething (m, 7);
destroyMyClass (m);
>}

Indeed. I was thinking about him actually accessing
members of types that don't exist in C though.
Nope, not impossible, but like the above, stub city et al,
which can be a real pain to being productive unless
isolated cases.
--
Greg Comeau / 20 years of Comeauity! Intel Mac Port now in alpha!
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?

[Roland Pibinger]

Re: C++ library access from C

On 30 Sep 2006 09:22:43 -0400, comeau@panix.co m (Greg Comeau) wrote:

>Nope, not impossible, but like the above, stub city et al,
>which can be a real pain to being productive unless
>isolated cases.

Yes, that's true. A tool may be helpful: http://www.swig.org/

Best regards,
Roland Pibinger