CODEWITHSUNDEEP
cstdoutncurses
lowq
lowq

Reputation: 628

Ncurses and Linux pipeline

I'd like to write a simple program using ncurses for displaying some data. I would then like for the program to write to stdout in such a way that I can then use a pipe (|) on the command line to pipe some data out.

My current attempt doesn't work. I can see the "GOT HERE"'s in a file using '>', but there's a whole bunch of other stuff. The program also exits immediately.

#include <stdio.h>
#include <ncurses.h>


int main(int _argc, char ** _argv)
{
    initscr();          /* Start curses mode          */

    printw("Hello World !!!");  /* Print Hello World          */

    refresh();          /* Print it on to the real screen */

    getch();            /* Wait for user input */

    printf("GOT HERE");

    endwin();           /* End curses mode        */

    printf("GOT HERE");

    return 0;
}

This is the final output using >

^[[?1049h^[[1;29r^[(B^[[m^[[4l^[[?7h^[[H^[[2JHello World !!!^MGOT HERE^[[29;1H^[[?1049l^M^[[?1l^[>GOT HERE

Is it possible to use stdout through a pipeline and ncurses at the same time?

Upvotes: 4

Views: 8022

Answers (2)

Thomas Dickey
Thomas Dickey

Reputation: 54475

By default, curses writes to the standard output, which is where your pipe goes. But there are two different initialization functions for curses: initscr and newterm. The latter lets you do what was asked, like this:

#include <stdio.h>
#include <ncurses.h>


int main(int _argc, char ** _argv)
{
    newterm(NULL, stderr, stdin);          /* Start curses mode          */    
    printw("Hello World !!!");  /* Print Hello World          */    
    refresh();          /* Print it on to the real screen */    
    getch();            /* Wait for user input */    
    printf("GOT HERE");    
    endwin();           /* End curses mode        */    
    printf("GOT HERE");    
    return 0;
}

Further reading: manual page for newterm and initscr.

Upvotes: 6

flukus
flukus

Reputation: 1028

This is 5 years old now and you've probably moved on, but this was the top of my search results so I thought I'd add the solution I found. After a lot of messing about with trying to get pipes to work in code like bash example above, I finally found someone that hinted in the right direction with the newterm command. The only trick is to open a new tty and to use newterm instead of initscr:

#include  <stdio.h>
#include <ncurses.h>

int main(int argc, char ** argv) {

  FILE *f = fopen("/dev/tty", "r+");
  SCREEN *screen = newterm(NULL, f, f);
  set_term(screen);

  //this goes to stdout
  fprintf(stdout, "hello\n");
  //this goes to the console
  fprintf(stderr, "some error\n");
  //this goes to display
  mvprintw(0, 0, "hello ncurses");
  refresh();
  getch();
  endwin();

  return 0;
}

With this you can pipe stdout and stderr wherever you want but have an ncurses session. I'm not sure how portable it is or if there are any other catches, just glad to find a solution that worked.

Upvotes: 13

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