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Old 06-14-2012, 04:16 AM   #1
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Can a process redirect stdout and still use ncurses in a terminal?

Hi all.

Hopefully I can explain this OK, but if not I am happy to try to expand my problem.

I am using ncurses to display my program output in a terminal. I would also like to redirect stdout and stderr to my own logging functions so that any third-party software errors etc. are picked up and recorded/displayed as part of my logs.

However, ncurses appears to use stdout to display its windows in the terminal so when I redirect stdout, the ncurses output gets redirected to my logging output too. It then also obviously stops displaying the ncurses window in the terminal.

So, can (and if so how?), the stdout be redirected and yet ncurses still be used to display in the terminal?
Old 06-14-2012, 06:17 AM   #2
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you need to NOT write to stdout... maybe you can chuck output to syslog, or open a log file directly?
Old 06-14-2012, 08:37 AM   #3
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Er, I knew my description would be not as good as it could be.

My aim was to catch all the printf and similar output from third-party code I have no control over, from stdout and redirect it to my own logger. This logger can then record and update the ncurses display with its own formatted output. Except the ncurses displays using stdout, so any re-direction caused ncurses to be logged. And no re-direction caused printf's to corrupt the display.

Thanks for answering though, because on the plus side, as always happens when you post and ask for help, writing the post seems to clarify things in your mind and after days of work and searching a solution presents itself...

For anyone else that needs this:

1. Instead of using initscr(), use newterm() with the default terminal file desciptor to start ncurses:

FILE *fd = fopen("/dev/tty", "r+");
SCREEN *scr = newterm(NULL, fd, fd);

This opens a new ncurses terminal bypassing stdin and stdout (I think). stdout can then by redirected wherever:

int newfd;
dup2(newfd, 1);

I then use setvbuf(stdout, NULL, _IONBF, 0) to make stdout unbuffered. This doesn't seem to automatically pass printf's with no "\n" through, so in an ncurses update function, I call fflush(stdout) every pass to punt through the messages. And hey presto I seem to be getting there!

Don't forget delscreen(scr) when you're done with ncurses.



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