Clearing a terminal similar to man page using C

Question

I want to read a text file and display it. But I need to print it on terminal, similar to the man page (linux). That is, when scrolled up, it shouldn't go beyond the first line and scrolling down shouldn't go beyond the last line. I have to program it only in C. I shouldn't use any tools. My current coding for clearing a terminal alone is,

#include<stdio.h>

main()
{
printf("\033[2J");
printf("\033[0;0f");
FILE *ffp;
char c;

ffp=fopen("help.txt","r");
while((c=getc(ffp))!=EOF)
    printf("%c",c);
}

Kindly guide me. Thanks in advance.

UPDATED:

main()
{
FILE *ffp;
char c;


ffp=fopen("help.txt","r");

FILE *less = popen("less", "w");
while ((c = getc(ffp)) != EOF) {
  fputc(c, less);
}
}

@maverik Yes. But it's a pre-defined tool. I need to get it programmed, as I cleared the terminal using a C code. — Gomathi, Dec 20 '12 at 10:20
Is this some kind of homework ? In real life you'd use `less` (or whatever is set in the `PAGER` environment variable). No C is ever required here (and it goes against the UNIX spirit to use C for this task). — Alexandre C., Dec 20 '12 at 10:26
@AlexandreC. Yes. It's a part of my project. I'll try PAGER enironment variable. Thanks. — Gomathi, Dec 20 '12 at 10:33

score 1 · Answer 1 · edited May 23 '17 at 11:56

1

try something like this,,

#include <stdio.h>

int
main ()
{
    fputs("output1\n",stdout);
    fputs("output2\n",stdout);
    fputs("\033[A\033[2K\033[A\033[2K",stdout);
    rewind(stdout);
    ftruncate(1,0); /* you probably want this as well */
    fputs("output3\n",stdout);
    fputs("output4\n",stdout);
    return 0;
}

SOURCE: Clearing output of a terminal program Linux C/C++

edited May 23 '17 at 11:56

Community

1
1

answered Dec 20 '12 at 10:20

Adeel Ahmed

1,591
8
10

I already viewed that answer. It only clears the previous two lines. My coding clears even an entire screen! – Gomathi Dec 20 '12 at 10:22
Thanks. But clearing isn't a matter, which I can already do using my code. I want it similar to a man page. Please read my question again. – Gomathi Dec 20 '12 at 10:35

Barmar · Accepted Answer · 2012-12-20T10:35:22.237

1

FILE *less = popen("less", "w");
while ((c = getc(ffp)) != EOF) {
  fputc(c, less);
}

more and less are the programs that implement scrolling through a file or pipe a screenful at a time.

edited Dec 20 '12 at 10:35

answered Dec 20 '12 at 10:25

Barmar

741,623
53
500
612

Thank you. What header file should I use for less? I'm getting an undeclared variable error. – Gomathi Dec 20 '12 at 10:31
I've added the declaration. Couldn't you look in the man page for `popen()`? – Barmar Dec 20 '12 at 10:34
Thanks and sorry. But the file is not getting displayed. I have updated my code in question. – Gomathi Dec 20 '12 at 10:42
Is the `less` program in your `$PATH`? – Barmar Dec 20 '12 at 10:45
If I use 'more' it displays the file. But it makes no difference. It still can be scrolled up to see the remaining part of the terminal! – Gomathi Dec 20 '12 at 10:58
That's just the way terminal emulator scrollback buffers work. – Barmar Dec 20 '12 at 10:59
I read that, there are certain tools for creating man page, like Troff and Groff. Is that the only way then? Programming in C seems impossible. – Gomathi Dec 20 '12 at 11:06
This has nothing to do with the tools used for creating man pages. `man` just uses $PAGER to display the file. – Barmar Dec 20 '12 at 11:07

Clearing a terminal similar to man page using C

2 Answers2