Re: Link to C++ library

[Pascal Bourguignon]

> From: "Yen-Ju Chen" <yjchenx@hotmail.com>
> Date: Tue, 10 Sep 2002 17:55:15 -0400
> 
> 
>   Which version of GCC are you using ? I use 3.0.4.

I still have 2.95.3:
[pascal@thalassa]$ g++ --version
2.95.3

>   How can you compile .c using g++ and .m using gcc
>   in the same GNUmakefile ?

Actually, when  specifying CC=g++ in GNUmakefile,  the makefile system
of GNUstep will use g++ to compile everything, both .c and .m files.

>   If I use CC=gcc++ at the beginning,
>   it will complain that g++ unrecognize option '-MP'
>   and cc1obj invalide option '-fconstant-string-class=NSConstantString'


>   Here is what I have:
> 
>   g++ main.m -c \
>        -MMD -MP -DGNUSTEP -DGNUSTEP_BASE_LIBRARY=1 ...
>        -o shared_objc/ix86/freebsd/gnu-gnu-gnu/main.o
>         ...
> 
>   So I use CC=gcc to get the .o file first.
>   Then use CC=g++ again, I got the error in previous message...
> 
>   So weird... need to look into it....

The fact  is, when you want to  link C++ code with  C (or Objective-C)
code,  you have to  take care  of the  name mangling  done by  the C++
compiler.  One way  to do it is to use only  a C++ compiler, therefore
you only generate mangled names (for C and C++ objects) and there's no
linking problem.  Another option is to  use extern "C"{ ... } in C/C++
code. See attached files.

>   Yen-Ju
> 
> >From: Pascal Bourguignon <pjb@informatimago.com>
> >Reply-To: <pjb@informatimago.com>
> >To: yjchenx@hotmail.com
> >CC: help-gnustep@gnu.org
> >Subject: Re: Link to C++ library
> >Date: Tue, 10 Sep 2002 23:28:28 +0200 (CEST)
> >
> > > From: "Yen-Ju Chen" <yjchenx@hotmail.com>
> > > Date: Tue, 10 Sep 2002 16:55:52 -0400
> > >
> > >
> > >   Thanx a lot. It helps.
> > >   But can I directly link Objective-C to C++ throught
> > >   the C interface which the C++ library offers ?
> > >
> > >   After apply the CC=g++, the error message becomes
> > >
> > >   .../libgnustep-base.so: undefined reference to '__objc_msg_forward'
> > >   .../libgnustep-base.so: undefined reference to '__objc_msg_thread_add'
> > >   .../libgnustep-base.so: undefined reference to 
> >'__objc_msg_thread_remove'
> > >
> > >   Or do I need to write a C library as the bridge between Objective-C 
> >and
> > > C++ ?
> >
> >You seem to be missing the  Objective-C runtime. I still use a GNUstep
> >some months old,  but it's makefiles automatically cite  -lobjc on the
> >link line.  I have something like:
> >
> >  g++ -rdynamic \
> >       -o MyApp.app/ix86/linux-gnu/gnu-gnu-gnu/MyApp \
> >       shared_obj/ix86/linux-gnu/gnu-gnu-gnu/MyObjects.o ... \
> >       -L/home/pascal/GNUstep/Libraries/ix86/linux-gnu/gnu-gnu-gnu \
> >       -L/home/pascal/GNUstep/Libraries/ix86/linux-gnu \
> >       -L/local/gnustep/Local/Libraries/ix86/linux-gnu/gnu-gnu-gnu \
> >       -L/local/gnustep/Local/Libraries/ix86/linux-gnu \
> >       -L/local/gnustep/Network/Libraries/ix86/linux-gnu/gnu-gnu-gnu \
> >       -L/local/gnustep/Network/Libraries/ix86/linux-gnu \
> >       -L/local/gnustep/System/Libraries/ix86/linux-gnu/gnu-gnu-gnu \
> >       -L/local/gnustep/System/Libraries/ix86/linux-gnu \
> >       -L/local/gnustep/System/Libraries/ix86/linux-gnu \
> >       -lgnustep-gui -lgnustep-base -lobjc \
> >       -lz -lcallback -lavcall -lxml2 -lz -lm -lgmp -lpthread -ldl -lm \
> >       $(MyApp_OTHER_LIBRARIES)
> >
> >
> > >   Thanx again.
> > >
> > >   Yen-Ju
> > >
> > > >From: Pascal Bourguignon <pjb@informatimago.com>
> > > >Date: Tue, 10 Sep 2002 22:38:13 +0200 (CEST)
> > > > > From: "Yen-Ju Chen" <yjchenx@hotmail.com>
> > > > > Date: Tue, 10 Sep 2002 15:52:52 -0400
> > > > >
> > > > >   I try to use the id3lib (http://www.id3lib.org), which is a
> > > > >   C++ library, but offer the C interface.  But I met a problem
> > > > >   about linking between id3lib and standard C++  library.  Is it
> > > > >   possible to use such C++ library with C interface in GNUstep ?
> > > >
> > > >I  do  link  routinely   C++  libraries  into  GNUstep  /  Objective-C
> > > >applications without any problem, passing thru a C interface.
> > > >
> > > >Here  is an example  of GNUmakefile  I used  lately. The  only notable
> > > >thing  is  the  use  of  the  g++ compiler  (CC=g++)  to  compile  the
> > > >MyCppLibCalls.c  file, which  contains  only simple  C functions  each
> > > >sending  a message  to a  C++ object  from libMyCppLib.a,  which  is a
> > > >library of C++ objects.


-- 
__Pascal_Bourguignon__                   http://www.informatimago.com/
----------------------------------------------------------------------
 The name is Baud,...... James Baud.

stuff.h
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stuff.h++
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stuff.c++
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main.m
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Makefile
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compile.log
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