Re: recent gnulib has problems with read, write and close within structs

[Joël Krähemann]

thank you.

On Sun, Sep 13, 2020 at 11:11 PM Bruno Haible <bruno@clisp.org> wrote:
>
> Hi Joël,
>
> > Because recent gnulib has problems with read, write and close as
> > struct fields. I am still using:
> >
> > gnulib$ git log
> > commit 2d431ac35c4943a3655c07ba91870d2323321b43 (HEAD -> master,
> > origin/master, origin/HEAD)
> >
> > Here is my code:
> >
> > https://git.savannah.nongnu.org/cgit/gsequencer.git/tree/ags/object/ags_application_context.h#n112
> >
> > Actually it fails here:
> >
> > https://git.savannah.nongnu.org/cgit/gsequencer.git/tree/ags/X/ags_xorg_application_context.c#n431
> >
> > Here is a snipped of the terminal output:
> >
> > ags/X/ags_xorg_application_context.c:89: warning: "_GNU_SOURCE" redefined
> >    89 | #define _GNU_SOURCE
> >       |
> > In file included from <command-line>:
> > ././ags/config.h:605: note: this is the location of the previous definition
> >   605 | # define _GNU_SOURCE 1
> >       |
> > In file included from ./ags/audio/midi/ags_midi_builder.h:29,
> >                  from ./ags/libags-audio.h:144,
> >                  from ./ags/X/ags_xorg_application_context.h:29,
> >                  from ags/X/ags_xorg_application_context.c:20:
> > ags/X/ags_xorg_application_context.c: In function
> > 'ags_xorg_application_context_class_init':
> > ags/X/ags_xorg_application_context.c:431:24: error:
> > 'AgsApplicationContextClass' {aka 'struct
> > _AgsApplicationContextClass'} has no member named '_write'; did you
> > mean 'write'?
> >   431 |   application_context->write = ags_xorg_application_context_write;
> >       |                        ^~~~~
> > ags/X/ags_xorg_application_context.c:432:24: error:
> > 'AgsApplicationContextClass' {aka 'struct
> > _AgsApplicationContextClass'} has no member named '_read'; did you
> > mean 'read'?
> >   432 |   application_context->read = ags_xorg_application_context_read;
> >       |
>
> Gnulib defines functions like 'read', 'write', 'close', etc. as C preprocessor
> macros, in order to avoid conflicts at the linker level. This is essential for
> the operation of Gnulib. So, 'write' may be defined to 'rpl_write' or to
> '_write', depending on the platform. (For some compilers, it would be possible
> to do this mapping at the C compiler level as opposed to the C preprocessor
> level. But this does not generalize to all compilers, therefore we are 
> avoiding
> this approach.)
>
> Yes, unfortunately this can produce an error if you define a struct with a
> member 'write', then #include <unistd.h>, then use code that looks up the
> member 'write' - because at this point, 'write' expands to 'rpl_write' or
> '_write'.
>
> The workaround is simple: Make sure that you include the corresponding file -
> here <unistd.h> - before the struct definition. That is, in this case,
> at the beginning of ags/object/ags_application_context.h, add
>   #include <unistd.h>
>
> Bruno
>