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?

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.

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.

vvv The Red Means Happy!

Kleido-0, time to update your title thingy. Unless you're hoping for some negative rep

>And don't tell me it's off topic because you can put assembly into your C code.
It's off-topic because you can't do it portably. First, embedding assembly code into C source is a common extension, but not blessed by the standard. Second, assembly itself is dreadfully nonportable. Now, if the question mentioned a compiler, operating system, and architecture then we could get into mentioning assembly. Of course, it would still be off-topic because it isn't C.

>I was hoping you would do that :P
I have done that, just not with the code you linked to. In a previous life I implemented a large portion of the C run-time and standard library to work with a very broken OS.