Thread: printf without include??

He wants you to write your own console IO without using any standard headers? Good luck.

Quzah.

Originally Posted by quzah

He wants you to write your own console IO without using any standard headers? Good luck.

Quzah.

Actually, it's not to hard.

There's some code over at http://www.osdever.net about writing C functions without the RTL (Run-Time Library).

Basically, all you do is access the memory for the video, and then put your text onto the screen.

If you don't know how to start, you're probably mistunderstanding the assignment, because writing your own I/O library (no matter how simplistic) without any headers is an exercise in VERY low level programming. Try this:

Code:

int main(void)
{
  printf("a");

  return 0;
}

It's wrong on so many levels to be scary, but it may happen to work. It sounds like your teacher can't recognize undefined behavior and wants to show you a "neat trick".

>"Well that would be easy", but you can't use putchar() or even strlen()!?
Nope, you have to write them yourself if you want them. strlen is a no brainer, but putchar is surprisingly difficult to implement. Especially if you aren't allowed to include any headers.

Originally Posted by asun

i want to

Code:

printf("a");

without using

Code:

#include<stdio.h>

Code:

int printf(const char *format, ... );

int main(void)
{
   printf("a");
   return 0;
}

...Provided the proper library is linked?

Ok maybe not as bad as I thought lol

Code:

int mystrlen(char *sz) {
	int c, count=0;
	while((c=sz[count++]) != '\0');
	return --count;
}

Ok the putchar... I think I found something, check it out http://www.uclibc.org/cgi-bin/cvsweb....1&view=markup

For those who don't know, try googling:
filetype:c putchar

That's what I used to find the page above just in case you all wanted to know.

>Ok maybe not as bad as I thought lol
Yes, most of the string functions are trivial.

>Ok the putchar... I think I found something
Have you walked all of the way through the macro maze to see what's really happening?

I don't know how you would do it but maybe you could use assembly? I know you can print stuff on the screen with that. And don't tell me it's off topic because you can put assembly into your C code.

Originally Posted by Kleid-0

Ok maybe not as bad as I thought lol
...snip...
Ok the putchar... I think I found something, check it out http://www.uclibc.org/cgi-bin/cvsweb....1&view=markup

For those who don't know, try googling:
filetype:c putchar

That's what I used to find the page above just in case you all wanted to know.

The linked code wouldn't be allowed by the OP's definition. They include their own header file, "_stdio.h", which includes who knows what. Oh, wait, here it is:

Code:

/* Copyright (C) 2004       Manuel Novoa III    <[email protected]>
 *
 * GNU Library General Public License (LGPL) version 2 or later.
 *
 * Dedicated to Toni.  See uClibc/DEDICATION.mjn3 for details.
 */

#define _GNU_SOURCE

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#ifdef __UCLIBC_HAS_WC
...snip...

So yeah, that's not going to cut it.

Quzah.

Wouldn't you at least need write()? I mean, the kernel doesn't actually let you send stuff to the console without passing it through it, does it?

Furthermore, as suggested in the first reply to mine, most kernels now don't simply let you grab ahold of the hardware. So I suspect that you fiddling with the video memory directly wouldn't be appreciated either. Could be wrong, but that's what I'm thinking. (Oh, and that link was dead when I went to look at it.)

Quzah.