Linux C Ncurses issue

Question

I'm having a strange problem with Ncurses in C that I can't seem to find documented anywhere, nor on the web. Maybe I'm not using the correct search terms?

Here is the problem:

I have several windows and panels and LOTs of code. It all works perfectly UNTIL this happens:

mvwprintw(windowptr[i], y, x, NULL); <-- That NULL value is what sets off the bomb

I would expect that a NULL string would simply print a string of 0 length, but that's not what happens. What actually happens is that it corrupts all of my windows/panels. It seems to be somehow deleting all previously written chars and disabling the displaying of new chars on all windows / panels except the current window / panel. The current window / panel does not get blanked, but no new chars can be printed to it.

Is this a bug? ... or maybe an undocumented feature?

Here's my Ncurses version:

$ dpkg -l | grep -i ncurse
ii  libncurses5:amd64                             6.0+20160213-1ubuntu1                           amd64        shared libraries for terminal handling
ii  libncurses5:i386                              6.0+20160213-1ubuntu1                           i386         shared libraries for terminal handling
ii  libncurses5-dev:amd64                         6.0+20160213-1ubuntu1                           amd64        developer's libraries for ncurses
ii  libncursesw5:amd64                            6.0+20160213-1ubuntu1                           amd64        shared libraries for terminal handling (wide character support)
ii  libncursesw5:i386                             6.0+20160213-1ubuntu1                           i386         shared libraries for terminal handling (wide character support)
ii  mtr-tiny                                      0.86-1ubuntu0.1                                 amd64        Full screen ncurses traceroute tool
ii  ncurses-base                                  6.0+20160213-1ubuntu1                           all          basic terminal type definitions
ii  ncurses-bin                                   6.0+20160213-1ubuntu1                           amd64        terminal-related programs and man pages
ii  ncurses-term                                  6.0+20160213-1ubuntu1                           all          additional terminal type definitions

Answer 1

Actually (there's no sample MCVE ) to test in this question), ncurses does check for this null pointer and is expected to ignore the printw which would be called after the wmove part.

To see this, follow the source-code:

• mvprintw is always a function call (due to the variable-length argument list)
• vw_printw is the next step, which calls
• _nc_printf_string , which sees the null-pointer for the format, and returns null,
• making vw_printw ignore the call.