C , linebreak without linefeed? - c

Question

Silly question but,
Is it possible to break a line on stdout without the line feed using printf();? If not, any tips on how I would overwrite 2+ lines, if possible?
I'm trying to generate sort of a progress bar but on multiple lines.
Any ideas?
EDIT:
So yeah I accepted the below answer although it won't work for my specific case.
I'm trying to overwrite 2+lines
rather than a single line.
printf("12345\r");
fflush(stdout);
printf("67890\n");
The result of which is $ ./a.out 67890
But what I'm trying to achieve is have 2+ lines be overwritten with new data.
Similar to a progress bar but on 2+ lines except I have a percentage number for some data.

Answer 1

To rewrite all (or part) of a line, you need to use the correct number of backspace characters. Eg:
printf("some text");
printf("\b\b\b\bstuff");
Will output:
some stuff
This is fine for simple stuff; for something more complex you should use ncurses which uses ANSI-escape cleverness to manipulate the cursor around the screen.

Answer 2

If your terminal (or, much more likely, terminal emulator) supports VT100-style escape sequences, you can print specific code sequences to control the cursor position, clear some or all of the screen/window, etc.
For example, to move the cursor up 1 line:
printf("\x1b[A");
fflush(stdout);
To move the cursor up 2 lines, either do that twice or:
printf("\x1b[2A"});
fflush(stdout);
These are commonly referred to as ANSI escape codes; the link is to a Wikipedia article that lists many of them. They were first implemented by the old DEC VT-100 terminal, which is emulated by most modern terminals and emulators.
And this:
printf("\x1b[J");
fflush(stdout);
will clear part of the screen, from the current cursor position to the bottom.
These sequences should be enough to do what you need. (They might not work in a Windows command window.)
More portably, if your system supports it, you can use termcap or terminfo to determine the proper command sequences for your current terminal (as determined by the $TERM environment variable). The tput command lets you do this on the command line; man tput for more information. In practice, you're unlikely to find a system these days that supports termcap or terminfo with a terminal that's not VT100-compatible; printing raw escape sequences is strictly not portable, but probably good enough.
A suggestion: your program should probably have an option to inhibit any such control sequences; for example, if a user who wants to redirect the output to a file won't want to have those escape sequences in the file. Some programs use control sequences only if they can determine that stdout is a terminal, but an explicit option is also a good idea.
*UPDATE: *
Here's a program I threw together that demonstrates how to do this with the terminfo. It should work on just about any Unix-like system.
#include <stdio.h>
#include <stdlib.h>
#include <curses.h>
#include <term.h>
#include <unistd.h>
int main(void) {
const char *term = getenv("TERM");
if (term == NULL) {
fprintf(stderr, "TERM environment variable is not set\n");
exit(EXIT_FAILURE);
}
setterm(term);
for (int i = 0; i < 10; i ++) {
putp(tparm(clr_eos));
printf("%d\n%d\n", i, i+1);
sleep(1);
putp(tparm(parm_up_cursor, 2));
}
return 0;
}