Printf and scanf

Printf and scanf

[Ankit Jain]

hi

this is a simple problem which somebody asked me and i
am not able to solve. if somebody here can help me out

i just want to know how scanf function can be used on
the place of printf and vice versa

thanks

ankit

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Re: Printf and scanf

[Arturas Moskvinas]

> hi
> 
> this is a simple problem which somebody asked me and i
> am not able to solve. if somebody here can help me out
> 
> i just want to know how scanf function can be used on
> the place of printf and vice versa

Scanf reads from STDIN and printf writes into STDOUT. I do not think
there is any way to change reading operation with writing... Of course
some alchemy might help you :)

I think you misinterpreted something...

Arturas Moskvinas

Re: Printf and scanf

[Eric Bambach]

On Sunday 05 June 2005 08:54 am, Arturas Moskvinas wrote:
> > hi
> >
> > this is a simple problem which somebody asked me and i
> > am not able to solve. if somebody here can help me out
> >
> > i just want to know how scanf function can be used on
> > the place of printf and vice versa
>
> Scanf reads from STDIN and printf writes into STDOUT. I do not think
> there is any way to change reading operation with writing... Of course
> some alchemy might help you :)
>
> I think you misinterpreted something...

I agree. At a most basic level printf copies its arguments into STDOUTs 
buffer. Scanf reads from STDINs buffer and copies to its arguments memory 
space. There is no way to make these functions behave differently. Perhaps 
with fprintf and fscanf you can make some magic...but its a silly exercise 
and would make code unholy and unreadable.
> Arturas Moskvinas
> -
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-- 
----------------------------------------
--EB

> All is fine except that I can reliably "oops" it simply by trying to read
> from /proc/apm (e.g. cat /proc/apm).
> oops output and ksymoops-2.3.4 output is attached.
> Is there anything else I can contribute?

The latitude and longtitude of the bios writers current position, and
a ballistic missile.

                --Alan Cox LKML-December 08,2000 

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Re: Printf and scanf

[Steve Graegert]

On 6/5/05, Ankit Jain <ankitjain1580@yahoo.com> wrote:
> hi

Hello,

> i just want to know how scanf function can be used on
> the place of printf and vice versa

Hmm, I think I do not understand your question.  Can you give an
example of what you want to achive?

Kind Regards

    \Steve

--

Steve Graegert <graegerts@gmail.com>
Independent Software Consultant {C/C++ && Java && .NET}
Mobile: +49 (176)  21 24 88 69
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Re: Printf and scanf

[Hendrik Visage]

On 6/5/05, Ankit Jain <ankitjain1580@yahoo.com> wrote:

> i just want to know how scanf function can be used on
> the place of printf and vice versa

In the Obfuscated C contest one of the first/early entries is one that
states "Using read to write" (Or something to similar extend, or
perhaps even using scanf to print). Reading that code is hackery, and
from my first glance at the code, it was don't with quote and macro
hackery.

Thus you could #define scanf __prinf and #define printf __scanf... or
something with similar confusing

-- 
Hendrik Visage
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Re: Printf and scanf

[Andriot]

Hendrik Visage wrote:

>On 6/5/05, Ankit Jain <ankitjain1580@yahoo.com> wrote:
>
>  
>
>>i just want to know how scanf function can be used on
>>the place of printf and vice versa
>>    
>>
>
>In the Obfuscated C contest one of the first/early entries is one that
>states "Using read to write" (Or something to similar extend, or
>perhaps even using scanf to print). Reading that code is hackery, and
>from my first glance at the code, it was don't with quote and macro
>hackery.
>
>Thus you could #define scanf __prinf and #define printf __scanf... or
>something with similar confusing
>  
>

Of course, it is not possible to use directly printf like a scanf ;)
But you can use printf to write some values into arguments when you call 
the function. This uses special caracters you put in the format string. 
And this should prevent you to call printf with a string the user wrote, 
because this is a very big security hole.

JP

Re: Printf and scanf

[joy merwin monteiro]

Now you have piqued my interest.......
what special characters??
any place on the net I can read up on this?

Joy


On 6/27/05, Andriot <andriot@6wind.com> wrote:
> Hendrik Visage wrote:
> 
> >On 6/5/05, Ankit Jain <ankitjain1580@yahoo.com> wrote:
> >
> >
> >
> >>i just want to know how scanf function can be used on
> >>the place of printf and vice versa
> >>
> >>
> >
> >In the Obfuscated C contest one of the first/early entries is one that
> >states "Using read to write" (Or something to similar extend, or
> >perhaps even using scanf to print). Reading that code is hackery, and
> >from my first glance at the code, it was don't with quote and macro
> >hackery.
> >
> >Thus you could #define scanf __prinf and #define printf __scanf... or
> >something with similar confusing
> >
> >
> 
> Of course, it is not possible to use directly printf like a scanf ;)
> But you can use printf to write some values into arguments when you call
> the function. This uses special caracters you put in the format string.
> And this should prevent you to call printf with a string the user wrote,
> because this is a very big security hole.
> 
> JP
> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
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> 


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