Re: Bison complains about undefined reference of my own data type

[Laurence Finston]

> You need to do it to interface to any library written in C (such as
> the standard C library for example). For example, try the following
> C++ code with and without 'extern "C"'. Without it, you won't be able
> to link. Fortunately, all your system headers already provide you with
> 'extern "C"' by default.
> 
> extern "C" void exit(int);
> int main()
> {
>   exit(0);
> }

Thank you for the information.  However, I was able to compile and link
with and without 'extern "C"' using GCC 3.3.3 on a system running 
GNU/Linux (SuSE).  I couldn't link when I compiled with `g++' and tried 
to link with `gcc', but the error didn't seem to have anything to do with 
the problem under discussion:

   mangle.o(.eh_frame+0x11): undefined reference to `__gxx_personality_v0'

Am I missing something here? Clearly, `extern "C"' has a purpose, or it 
wouldn't exist.  Does GCC do something special, or have I done something 
wrong?

It seems to me that if a compiler doesn't mangle any "unqualified" names, 
i.e., ones  declared outside of a namespace or a class, it should be possible 
to link
with the object file in which they are defined without the linker having to 
do anything special.  However, it's been a long time since I read
anything about this subject and this may be naive.

Laurence


On Fri, 28 Nov 2008, Samuel Tardieu wrote:

> >>>>> "Laurence" == Laurence Finston <address@hidden> writes:
> 
> Laurence> One thing you might have to look out for is "name-mangling"
> Laurence> which C++ compilers do.  You might have to turn it off for C
> Laurence> code by specifying C-linkage, e.g., "extern "C" foo(void);".
> Laurence> I've never had to do this for my own code, but I've seen it
> Laurence> in other people's.  I would have to review when it's
> Laurence> necessary; I don't know off the top of my head.
> 
> You need to do it to interface to any library written in C (such as
> the standard C library for example). For example, try the following
> C++ code with and without 'extern "C"'. Without it, you won't be able
> to link. Fortunately, all your system headers already provide you with
> 'extern "C"' by default.
> 
> extern "C" void exit(int);
> int main()
> {
>   exit(0);
> }
> 
> 
> 
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>