Re: waddch_literal()

[Thomas Dickey]

On Sun, Nov 24, 2002 at 06:19:38PM -0500, Sam Varshavchik wrote:
> I was using the wide character build of ncurses-5.3 with the electricfence 
> memory debugger, when it dumped core in waddch_literal().  A brief 
> investigation revealed the following possible explanation:
> 
> Consider an 80 character display.  Upon entry to waddch_literal, 
> win->_curx=79.
> 
> The culprit appears to be the following:
> 
> 152:    line->text[x++] = ch;
> 153:    /*
> 154:     * Provide for multi-column characters
> 155:     */
> 156:    if_WIDEC({
> 157:        if (wcwidth(CharOf(ch)) > 1)
> 158:            AddAttr(line->text[x++], WA_NAC);
> 159:    }
> 

Thanks.  I guess a quick (not complete fix) would be to change that to
something like (untested):

          if_WIDEC({
              int len = wcwidth(CharOf(ch));
              if (len > 1 && (x + len) < getmaxx(newscr))
                  AddAttr(line->text[x++], WA_NAC);
              else {
                  /* some logic to force ch to start on the next line */
              }
          }

> In the case where it dumped core:
> 
> #0  0x081d370c in waddch_literal (win=0x403dff9c, ch=
>        {attr = 0, chars = {38291, 0, 0, 0, 0}})
> 
> At line 152, the character is placed into the 79th position, and x is 
> incremented to 80.
> 
> Now, it appears that this unicode character takes up two character cells, 
> according to my wcwidth(), so line 158 appears to try to set 
> line->text[80]. The problem appears to be that the array is not big enough 
> for that, so it runs off the end of the array.
> 
> Well, obviously placing a two-cell character in the last character position 
> on the line is not going to work, still a casual inquiry does seem to 
> indicate that ncurses tries to do boundary checking in these kinds of cases.
> 
> Additionally, I do not know if there are any unicode chars that will claim 
> three character cell positions, but the unlikely occurence it might be 
> useful to adjust this code to handle very, very wide characters...
> 
> 
> 
> 
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-- 
Thomas E. Dickey <address@hidden>
http://invisible-island.net
ftp://invisible-island.net