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Re: <ncursesw/curses.h> and addnwstr

From: Thomas Dickey
Subject: Re: <ncursesw/curses.h> and addnwstr
Date: Fri, 17 Mar 2023 19:02:39 -0400

On Fri, Mar 17, 2023 at 07:15:26PM +0100, Florian Weimer wrote:
> ocaml-curses has a configure check like this
>     AC_MSG_CHECKING(for wide character support in ncurses library)
>     AC_TRY_LINK(
>       [#include <wchar.h>
>        #include CURSES_HEADER
>       ],
>       [wchar_t wch = 0;
         ^^^^^^ this is declared via wchar.h, but the wide-character curses.h
                would include that, making the #include redundant.
>        addnwstr(&wch, 1);],
>       [AC_MSG_RESULT(yes)
>        AC_DEFINE(HAVE_WIDE_CURSES, 1, [Defined if ncurses library includes 
> wide character support])
>        BOOL_WIDE_CURSES="true"],
>       [AC_MSG_RESULT(no)])
> CURSES_HEADER in our builds is <ncursesw/curses.h>.  But curiously, that
> does not declare define, only <curses.h> does.  The symbol is defined in
                   ^^ not sure what you're indicating here
> libncursesw.so.6.2, though, which is why this issue is not apparent with
> current compilers which still support implicit function declarations.
> How should we resolve this?  Is there a better function for ocaml-curses
> to probe?  What about portability beyond ncurses?

I'd check if cchar_t is declared, to first get the proper header.
That should only be declared in the wide-character headers (because
it's only used for the wide-character functions of X/Open Curses).

But the wide-character features also (even for X/Open Curses) have
to have a symbol defined to declare them.  There's a section in
the ncurses manpage mentioning that:

            •   Alternatively,   you   can  enable  the  feature  by  defining
                NCURSES_WIDECHAR with the caveat that some other  header  file
                than  curses.h  may require a specific value for _XOPEN_SOURCE
                (or a system-specific symbol).

(actually, NetBSD doesn't require a symbol, but that's in the 60% which
it hasn't implemented yet :-)

Thomas E. Dickey <dickey@invisible-island.net>

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