interesting problem

[kris.c]

hi, its been some time since i have posted anything on this forum.. anyway, here goes:

 void abc(void)
   {

     < TO BE FILLED UP >
  
  }

 int main()
   {
     int i=10;
     abc();
     i=1;
     printf(" i = %d\n",i);
    return 0;
   }

This program should print

  
   i=10

The problem is to write the function abc() to get the required output

The function abc() takes in no arguments and returns void..

**** WE ARE NOT ALLOWED TO USE "printf()" INSIDE abc() ****


This is what i could think of :
Instructions are stored in a contiguous manner.. If I can cleverly modify Program Counter to skip the statement

 
   i=1;

and continue execution from the statement ,

    printf(" i = %d\n",i);

The problem can be solved..

I have no idea how to actually do it.. Can someone help me? Or is there a better method?

[King Mir]

I have no idea. if abc() could take arguements, then I could think of a that could sort of work (change i after i=1, but before the printf call). If abc() can be a macro you write another function that takes the address of i as a parammiter and uses that. eg:

Of course the are other ways to print to the screan besides printf(). But I assume that's not what you're asking.

[kris.c]

>Of course the are other ways to print to the screan besides printf(). But I assume that's not what you're asking
yeah.. we are not allowed to actually use calls to prinf stuff onto the screen.. and
abc() is given to be a function..

[OnionKnight]

If abc() has to be called before i=1; then I deem this impossible. Otherwise you could make i a global variable and just have abc() set it to 10.

[King Mir]

If you make i a global variable, then you could make a seperate thread change i to 10 several times over. Chances are it will be 10 before printf() is called.

The other idea I have is if you could ask windows for a pointer the the program stack, where i is stored. By I don't know if that's possible.

But in short, there is no standard way to skip a C command like that.

[King Mir]

Here's a thought: Somewhere I read that static variables are stored in memmory just before stack variables. If this is true, you could create a static variable inside abc(). Get the address, increment it, and you have the adress of i. The rest is the same as above.

I have real doubts that that would work, but it's a thought.

Edit: yeah, this did not work on my compiler.

[kris.c]

well, this appeared in an interview of a famous software company.. I guess the problem is not unsolvable..
What we could think of was : Is there anyway we can get the address where "main()" starts? Does anyone know how many bytes are allocated for each instruction? Is it one "word" per instruction?
Then we can somehow create a skip as required.. I am not able to get anything concrete out of this though..
> If you make i a global variable
" i " is declared inside main() as per the pproblem description.

>If abc() has to be called before i=1;
Yes that unfortunately is the case..

[Dave_Sinkula]

The intended answer most likely makes you define undefined behavior, so it's a bad idea to learn it.

[kris.c]

hmmm.... so, is there really a way out of this?

[King Mir]

Yeah, there is definately no standard way to do this. If this is part of an interview then it is a question about the language, not about your knowledge of how to get around it.

So the correct answer is that there is way to skip a command in C like that.

[kris.c]

>>So the correct answer is that there is way to skip a command in C like that.
duh?? was that a typo? or am i too sleepy?

[Dave_Sinkula]

Maybe I mis-skimmed some of the early replies. Perhaps this question is looking for proprocessor abuse. Something like:

void abc(void) 
{
   #define printf(x,y) puts(" i = 10")
}

Or maybe,

void abc(void)
{
   puts(" i = 10"), exit(1);
}

If so, what are they teaching you instead of how to code?

[OnionKnight]

Maybe I mis-skimmed some of the early replies. Perhaps this question is looking for proprocessor abuse.

void abc(void)
{
   #define printf(x,y) puts(" i = 10")
}

If so, what are they teaching you instead of how to code?

Wouldn't that macro only be available inside abc()?

edit: Seems not. :|

[kris.c]

yeah, something like that does work after all.. But I think I had written that
" we are not allowed to actually use calls to print stuff onto the screen.."
so, we have to mess around with the mem to get it done I guess

[Salem]

Not this stupid exercise again

> Or is there a better method?
Find a better book, or find a better teacher.