Using C functions in a C++ program

[ruffiano]

A colleague of mine who is a C developer wrote several functions in C
which I now need to invoke in my C++ application. This is normally not
a problem except that the header file that he wrote contains also
several structures and #defines, which I need to use in my C++
application.

What is the best way to use the C functions, structures and defines in
my code without upsetting the compiler / linker?

For the C functions I know I need to use extern "C" { ...}. But how do
I get to include the structures and the defines? If I include the
header file in my C++ code, then the linker will fail.

Any help is greatly appreciated.

Thanks.

[Noah Roberts]

Re: Using C functions in a C++ program


ruffiano wrote:

A colleague of mine who is a C developer wrote several functions in C
which I now need to invoke in my C++ application. This is normally not
a problem except that the header file that he wrote contains also
several structures and #defines, which I need to use in my C++
application.
>
What is the best way to use the C functions, structures and defines in
my code without upsetting the compiler / linker?
>
For the C functions I know I need to use extern "C" { ...}. But how do
I get to include the structures and the defines? If I include the
header file in my C++ code, then the linker will fail.

You can embed the C functions and structures in a namespace:

namespace CFunctions {

#include "CHeader.h"

};

Now you refer to them as CFunctions::fun ction() and such and it won't
clobber your global namespace with names you already have.

You can also use preprocessor stuff to undefine and redefine your
macros where needed. I don't know if push/pop and undef are standard
but they are rather common.

[Frederick Gotham]

Re: Using C functions in a C++ program

ruffiano posted:

A colleague of mine who is a C developer wrote several functions in C
which I now need to invoke in my C++ application. This is normally not
a problem except that the header file that he wrote contains also
several structures and #defines, which I need to use in my C++
application.

You'll have your files like:

apple.hpp
table.hpp

apple.cpp
table.cpp
disk.cpp

Your colleague's source files should have the extension ".c" -- most
compilers take this to mean that it should be compiled as C. Make sure though
that you go through the compiler options, paying specific attention to
whether it's compiled as C89 or as C99.

What is the best way to use the C functions, structures and defines in
my code without upsetting the compiler / linker?
For the C functions I know I need to use extern "C" { ...}. But how do
I get to include the structures and the defines? If I include the
header file in my C++ code, then the linker will fail.

Why does the linker fail?

--

Frederick Gotham

[Ian Collins]

Re: Using C functions in a C++ program

Noah Roberts wrote:

ruffiano wrote:
>

>>A colleague of mine who is a C developer wrote several functions in C
>>which I now need to invoke in my C++ application. This is normally not
>>a problem except that the header file that he wrote contains also
>>several structures and #defines, which I need to use in my C++
>>application .
>>
>>What is the best way to use the C functions, structures and defines in
>>my code without upsetting the compiler / linker?
>>
>>For the C functions I know I need to use extern "C" { ...}. But how do
>>I get to include the structures and the defines? If I include the
>>header file in my C++ code, then the linker will fail.

>
>
You can embed the C functions and structures in a namespace:
>
namespace CFunctions {
>
#include "CHeader.h"
>
};
>
Now you refer to them as CFunctions::fun ction() and such and it won't
clobber your global namespace with names you already have.
>

But then they will fail to link, assuming the C code is compiled with a
C compiler, all the symbols will be extern "C", not C++ mangled names.

Even if the C code is compiled with the C++ compiler, you will have to
conditionally include the namespace declaration for C++ compilation.

Better off just putting extern "C" round the inclusion of the header, or
better still conditionally included the wrapper in the header.

--
Ian Collins.

[Noah Roberts]

Re: Using C functions in a C++ program


Ian Collins wrote:

Noah Roberts wrote:

ruffiano wrote:

>A colleague of mine who is a C developer wrote several functions in C
>which I now need to invoke in my C++ application. This is normally not
>a problem except that the header file that he wrote contains also
>several structures and #defines, which I need to use in my C++
>application.
>
>What is the best way to use the C functions, structures and defines in
>my code without upsetting the compiler / linker?
>
>For the C functions I know I need to use extern "C" { ...}. But how do
>I get to include the structures and the defines? If I include the
>header file in my C++ code, then the linker will fail.

You can embed the C functions and structures in a namespace:

namespace CFunctions {

#include "CHeader.h"

};

Now you refer to them as CFunctions::fun ction() and such and it won't
clobber your global namespace with names you already have.

But then they will fail to link, assuming the C code is compiled with a
C compiler, all the symbols will be extern "C", not C++ mangled names.
>
Even if the C code is compiled with the C++ compiler, you will have to
conditionally include the namespace declaration for C++ compilation.
>
Better off just putting extern "C" round the inclusion of the header, or
better still conditionally included the wrapper in the header.

I misunderstood the problem. I figured he was dealing with names the
same as names he has.

[ruffiano]

Re: Using C functions in a C++ program

Better off just putting extern "C" round the inclusion of the header,


Hello Ian, I apologize in advance if I misunderstood you, but are you
basically suggesting writing the following:

extern "C"
{
#include "CHeader.h"
}

or better still conditionally included the wrapper in the header.

???


Ian Collins wrote:

Noah Roberts wrote:

ruffiano wrote:

>A colleague of mine who is a C developer wrote several functions in C
>which I now need to invoke in my C++ application. This is normally not
>a problem except that the header file that he wrote contains also
>several structures and #defines, which I need to use in my C++
>application.
>
>What is the best way to use the C functions, structures and defines in
>my code without upsetting the compiler / linker?
>
>For the C functions I know I need to use extern "C" { ...}. But how do
>I get to include the structures and the defines? If I include the
>header file in my C++ code, then the linker will fail.

You can embed the C functions and structures in a namespace:

namespace CFunctions {

#include "CHeader.h"

};

Now you refer to them as CFunctions::fun ction() and such and it won't
clobber your global namespace with names you already have.

But then they will fail to link, assuming the C code is compiled with a
C compiler, all the symbols will be extern "C", not C++ mangled names.
>
Even if the C code is compiled with the C++ compiler, you will have to
conditionally include the namespace declaration for C++ compilation.
>
Better off just putting extern "C" round the inclusion of the header, or
better still conditionally included the wrapper in the header.
>
--
Ian Collins.

[raxitsheth2000@yahoo.co.in]

Re: Using C functions in a C++ program

ruffiano,
refer this link,

http://developers.sun.com/prodtech/cc/articles/mixing.html

hope it will be helpful,

--
Raxit Sheth

[Ian Collins]

Re: Using C functions in a C++ program

ruffiano wrote:

>>Better off just putting extern "C" round the inclusion of the header,

>
Hello Ian, I apologize in advance if I misunderstood you, but are you
basically suggesting writing the following:
>
extern "C"
{
#include "CHeader.h"
}
>

Yes. Please reply inline, rather than top-posting.

>

>>or better still conditionally included the wrapper in the header.

>
???
>

in the header file, add

#ifdef __cplusplus
extern "C" {
#endif

before the definitions and

#ifdef __cplusplus
}
#endif

after them.

This is the usual way to make a header safe for inclusion in either C or
C++ code.

--
Ian Collins.

[Pete Becker]

Re: Using C functions in a C++ program

Ian Collins wrote:

>
Better off just putting extern "C" round the inclusion of the header,

Don't do that. It can cause horrible problems. The C header might pull
in other headers which, rightly, assume that they are not inside an
extern "C" block.

or

better still conditionally included the wrapper in the header.
>

Yup. Headers that will be used in both C and C++ need to conditionally
wrap their function prototypes in an extern "C" block:

#ifdef __cplusplus
extern "C" {
#endif

int my_funky_C_func (void);

#ifdef __cplusplus
}
#endif

[Greg Comeau]

Re: Using C functions in a C++ program

In article <4l23gaFe8imkU2 @individual.net >,
Ian Collins <ian-news@hotmail.co mwrote:

>ruffiano wrote:

>>>Better off just putting extern "C" round the inclusion of the header,

>>
>Hello Ian, I apologize in advance if I misunderstood you, but are you
>basically suggesting writing the following:
>>
>extern "C"
>{
>#include "CHeader.h"
>}
>>

>Yes.

IME, that forms should be avoided at almost all costs.
"funny things" start happening with typedef's, nested headers
and with compilers.

Only extern "C" what needs to be.

To quote Las Vegas: What happens in extern "C" stays in extern "C"
--
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?

[Pete Becker]

Re: Using C functions in a C++ program

Greg Comeau wrote:

In article <4l23gaFe8imkU2 @individual.net >,
Ian Collins <ian-news@hotmail.co mwrote:
>

>>ruffiano wrote:
>>

>>>>Better off just putting extern "C" round the inclusion of the header,
>>>
>>>Hello Ian, I apologize in advance if I misunderstood you, but are you
>>>basically suggesting writing the following:
>>>
>>>extern "C"
>>>{
>>>#include "CHeader.h"
>>>}
>>>

>>
>>Yes.

>
>
IME, that forms should be avoided at almost all costs.
"funny things" start happening with typedef's, nested headers
and with compilers.
>

And the standard explicitly prohibits including standard headers inside
any extern declaration, which in turn means that this isn't allowed if
CHeader.h uses any standard headers.

[ruffiano]

Re: Using C functions in a C++ program

raxitsheth2000@ yahoo.co.in wrote:

ruffiano,
refer this link,
>

http://developers.sun.com/prodtech/cc/articles/mixing.html

>
hope it will be helpful,
>
--
Raxit Sheth

Thanks for this article, which specifically addresses the problem I'm
dealing with. I also appreciate all the other suggestions. In the end,
I edited the header file as follows:

#ifdef __cplusplus
extern "C" {
#endif
.... /* body of header */
#ifdef __cplusplus
} /* closing brace for extern "C" */
#endif

P.S.: Is this the correct way to reply inline?