Re: Linux vs. libio

[Jamie Lokier <jamie dot lokier at cern dot ch>]

Per Bothner wrote:
> Jeffrey A Law <law@cygnus.com> writes:
> 
> > While I believe it was an unbelievably dumb thing for the glibc folks to
> > tie libio into the C library,
> 
> In other words, you don't think it is a reasonable goal to allow C
> stdio FILEs to be shared with C++ iostream streambufs?

The down side is it's not at all portable, so code that's written on
Linux will output differently on other platforms.

> The best way to synchronize (say) stdout with cout seems to be for
> them both to use the same buffer.  The requires (at least if you want
> efficiency) for them to use compatible data structures,

Only the /very/ few fields that are used by inline input/output
functions need to be shared.  Since they are simple data fields, sharing
those would be very easy even with many different kinds of C++ ABI.

Everything else, including vtable format and placement does not need to
be shared.  Just have the C library call functions (not virtual ones)
like "flush_my_output_stream" etc., and those functions would contain
the vtable lookup code.  Or alternatively, have an explicit /C/ vtable
as one of the shared fields and keep it that way for the C++ version.
C++ streams don't have to call that vtable; they merely have to provide
it.

-- Jamie