X-Git-Url: https://ncurses.scripts.mit.edu/?p=ncurses.git;a=blobdiff_plain;f=man%2Fcurs_getcchar.3x;h=43f97fd434113e46f9a7b12693d1d8cc1e8fd546;hp=01fc5f673c98ef033208591d1aa779ab872652af;hb=d97989d1e0db7282c723cabb44b991b951790006;hpb=1379ab3f6cc5b92256708ecc4129b57928d62cf4

diff --git a/man/curs_getcchar.3x b/man/curs_getcchar.3x
index 01fc5f67..43f97fd4 100644
--- a/man/curs_getcchar.3x
+++ b/man/curs_getcchar.3x
@@ -26,7 +26,7 @@
 .\" authorization.                                                           *
 .\"***************************************************************************
 .\"
-.\" $Id: curs_getcchar.3x,v 1.21 2019/03/24 00:59:45 tom Exp $
+.\" $Id: curs_getcchar.3x,v 1.23 2019/11/30 22:22:32 tom Exp $
 .TH curs_getcchar 3X ""
 .de bP
 .ie n  .IP \(bu 4
@@ -145,6 +145,53 @@ and \fBERR\fP otherwise.
 .PP
 Upon successful completion, \fBsetcchar\fP returns \fBOK\fP.
 Otherwise, it returns \fBERR\fP.
+.SH PORTABILITY
+The \fBCCHARW_MAX\fP symbol is specific to ncurses.
+X/Open Curses does not provide details for the layout of the \fBcchar_t\fP
+structure.
+It tells what data are stored in it:
+.bP
+a spacing character (\fBwchar_t\fP, i.e., 32-bits).
+.bP
+non-spacing characters (again, \fBwchar_t\fP's).
+.bP
+attributes (at least 16 bits, inferred from the various ACS- and WACS-flags).
+.bP
+color pair (at least 16 bits, inferred from the \fBunsigned short\fP type).
+.PP
+The non-spacing characters are optional,
+in the sense that zero or more may be stored in a \fBcchar_t\fP.
+XOpen/Curses specifies a limit:
+.RS 4
+.PP
+Implementations may limit the number of non-spacing characters that can be
+associated with a spacing character, provided any limit is at least 5.
+.RE
+.PP
+The Unix implementations at the time follow that limit:
+.bP
+AIX\ 4 and OSF1\ 4 use the same declaration with an array of 5 non-spacing
+characters \fIz\fP and a single spacing character \fIc\fP.
+.bP
+HP-UX\ 10 uses an opaque structure with 28 bytes,
+which is large enough for the 6 \fBwchar_t\fP values.
+.bP
+Solaris xpg4 curses uses a single array of 6 \fBwchar_t\fP values.
+.PP
+This implementation's \fBcchar_t\fP was defined in 1995
+using \fB5\fP for the total of spacing and non-spacing characters
+(\fBCCHARW_MAX\fP).
+That was probably due to a misreading of the AIX\ 4 header files,
+because the X/Open Curses document was not generally available at that time.
+Later (in 2002), this detail was overlooked when beginning to implement
+the functions using the structure.
+.PP
+In practice, even four non-spacing characters may seem enough.
+X/Open Curses documents possible uses for non-spacing characters,
+including using them for ligatures between characters
+(a feature apparently not supported by any curses implementation).
+Unicode does not limit the (analogous) number of combining characters,
+so some applications may be affected.
 .SH SEE ALSO
 .PP
 Functions: