[lug] [OT] g++ error message: declared with an exception specification?

[D. Stimits]

Scott Herod wrote:

> On Tue, 19 Nov 2002 rm at fabula.de wrote:
>
>
> >On Tue, Nov 19, 2002 at 10:30:50AM -0700, Scott Herod wrote:
> >
> >>Hello,
> >>
> >>Sorry of the OT post, but this is about the best group of people for it.
> >>
> >>I'm trying to write a bash built-in and compile it with g++.  This 
> is with
> >>bash 2-05a source from the GNU folk.  I'm getting errors like:
> >>
> >>../GNU/bash-2.05a/general.h:187: `sh_intfunc_t' declared with an 
> exception
> >>specification
> >
> >Rather silly question: if you compile an extension to a C-Program, 
> shouldn't
> >the exported functions be wrapped in 'extern C ...{ ...' ? Exception 
> specification
> >smells pretty much like C++-Linking ....
> >
> > ralfd
>
>
>
> I thought that was for going the other way, i.e. allowing a C++
> declaration to be understood by C?


Sounds like semantics. One would create a C++ extension to a C program 
by wrapping the C++ in extern "C" so it appears as C...both of you said 
the same thing. FYI, I have run into lots of functions that now have 
their own C++ prototype in GNU libs that now throw exceptions when they 
detect C++, and have best dealt with it by only using the extern "C" 
version without the exception throwing. What you observe is a bad sign 
that it is a reserved "hidden" symbol. You might try intentionally 
declaring everything involved as extern "C", as well as undefining 
__cplusplus while in that block.

Incidentally, if you cd to /lib/, and have libnss stuff, try this:
  nm libnss*.so | grep "_P[^a-zA-Z]"

Better yet, cd to /usr/include/ and run:
  grep -r "_P[^a-zA-Z]" *

D. Stimits, stimits AT attbi.com

>
> At any rate, from the dump with g++ -E I discovered that
> /usr/include/sys/cdefs.h is included which contains a few lines with:
>
>
>
> #undef	__P
> #undef	__PMT
>
> #ifdef __GNUC__
>
> /* GCC can always grok prototypes.  For C++ programs we add throw()
>    to help it optimize the function calls.  But this works only with
>    gcc 2.8.x and egcs.  */
> # if defined __cplusplus && __GNUC_PREREQ (2,8)
> #  define __THROW	throw ()
> # else
> #  define __THROW
> # endif
> # define __P(args)	args __THROW
>
>
>
> which of course screws up the __P definition previously made in one of the
> bash header files.  It also explains that nasty throw().  I suspect that
> there are some other #defines that I need to use to not hit this section
> of code.
>
> Scott
>
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