Writing an integer to stdout in text form using only write() to do writing

Question

I'm trying to write an integer in stdout, in text form, with only write() function and possibly while/if.

I want to write the integer out in text form, so that it's human-readable, but actually it is write out in binary form :

Here is what I tried :

main.c :

#include "my_put_nbr.h"
int main()
{
    my_put_nbr(43);
    return 0;
}

my_put_char.c :

#include <unistd.h>
int my_put_nbr(int nb)
{
        write(1, &nb, sizeof(nb));
        return 0;
}

So how can I write the integer out in text form with only write (or putchar) and conditions ?

PS : I must not use other libraries, so I can't use printf or whatever !

My github : link

text mode and binary mode are common in computer science, but here is a reminder for ones who don't understand what I mean by text form :

On a UNIX system, when an application reads from a file it gets exactly what's in the file on disk and the converse is true for writing. The situation is different in the DOS/Windows world where a file can be opened in one of two modes, binary or text. In the binary mode the system behaves exactly as in UNIX. However on writing in text mode, a NL (\n, ^J) is transformed into the sequence CR (\r, ^M) NL.

Quote from Cygwin.com

MAJ :

I found the answer:

#include "my_putchar.h"
/* 0x2D = '-'
 * 0x0 = NUL */
int my_put_nbr(int n)
{
        if (n < 0)
        {
                my_putchar(0x2D);
                n = -n;
        }

        if (n > 9)
        {
                my_put_nbr(n/10);
        }

        my_putchar((n%10) + '0');

        return 0;
}

Does your program include any header files? If yes, please post the entire program. — R Sahu, Jan 07 '16 at 17:28
So do you want to write the integer out in *text* form, so that it's human-readable, or do you want to write it out in *binary* form, with the expectation that another program will read the binary output? — , Jan 07 '16 at 20:46
@GuyHarris I want to write the integer out in text form, so that it's human-readable ! That's exactly the thing :) But actually I think my output is binary. — noraj, Jan 08 '16 at 07:20
It's not going to be reopened until you make the question understandable in the first place. — Carey Gregory, Jan 08 '16 at 23:50

score 2 · Answer 1 · answered Jan 07 '16 at 17:30

2

write is writing, but it is writing non-visible characters. You can see this with:

./myprogram | od -tx1

You will need to make the number in n (int value 23) into the string "23" before printing it.

One way:

  char buffer[16];
  snprintf(buffer, sizeof(buffer), "%d", n);
  write(1, buffer, strlen(buffer));

answered Jan 07 '16 at 17:30

John Hascall

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the number is `42` `$ ./main.out` => output : `�Ð�` and `$ ./main.out | od -tx1` => output : `0000053` – noraj Jan 07 '16 at 17:51
John Hascall : i don't want to use snprintf(), just write() – noraj Jan 07 '16 at 17:56
2

Then you will need to write the code to do the conversion to a string yourself. This page should help http://stackoverflow.com/a/9660930/2040863 – John Hascall Jan 07 '16 at 17:59
1

*i don't want to use snprintf(), just write()* Why do you expect writing a raw binary `int` to a character-based terminal to be readable? – Andrew Henle Jan 07 '16 at 18:00
@AndrewHenle I just re-coded `putchar`, `puts` and `strlen` with only write or/and boucle (while)or/and conition (if). I now want to write a put_int with just write() and ascii translation. I fact I want to use only system call and no additionnal library. – noraj Jan 07 '16 at 18:20
[Github](https://github.com/shark-oxi/my_functions) : here it is what I'm doing – noraj Jan 07 '16 at 18:36

Writing an integer to stdout in text form using only write() to do writing

1 Answers1