# write a single line C program whose output is the program itself

Discussion in 'C Programming' started by Puneet, Mar 16, 2005.

1. ### PuneetGuest

Hi ALL,

I have a silly question... (may be)

Can we write a single line C program whose output is the program
itself?

Puneet

Puneet, Mar 16, 2005

2. ### bjrnoveGuest

The c standard doesn't say anything about how a program is in memory.
So to make a program that does this on every system will probably not
be possible.
On some systems (like windows), if you compile your program without any
optimisation everything usaly end up in memory almost as you write the
program. This means that the following would print out it self on some
systems:

int main(void)
{
unsigned char *pCur = (unsigned char*)main, *pEnd = (unsigned
char*)emptyfunc;
while(pCur < pEnd) printf("%c", *pCur++);
}

void emptyfunc(void)
{
return;
}

This isn't something you usaly would want to do. It's much bether to
get a disassembler.

--
bjrnove

bjrnove, Mar 16, 2005

3. ### bjrnoveGuest

I forgot to declare emtyfunc, so you will have to add
void emptyfunc();
before main.

--
bjrnove

bjrnove, Mar 16, 2005
4. ### Shanmuhanathan TGuest

Puneet said,on 3/16/2005 3:53 PM:
> Hi ALL,
>
> I have a silly question... (may be)
>
> Can we write a single line C program whose output is the program
> itself?
>
>
> Puneet
>

you'll get lots of such programs...

--
Shanmu.

Shanmuhanathan T, Mar 16, 2005
5. ### Roy HillsGuest

On 16 Mar 2005 02:23:49 -0800, "Puneet" <>
wrote:
>Can we write a single line C program whose output is the program
>itself?

Ken Thompson mentions this in his classic paper "Reflections on
Trusting Trust" (from Communication of the ACM, Vol. 27, No. 8, August
1984, pp. 761-763).

This paper is available from:

http://www.acm.org/classics/sep95/

Roy

Roy Hills, Mar 16, 2005
6. ### Dave VanderviesGuest

In article <>,
Roy Hills <> wrote:
>On 16 Mar 2005 02:23:49 -0800, "Puneet" <>
>wrote:
>>Can we write a single line C program whose output is the program
>>itself?

>
>Ken Thompson mentions this in his classic paper "Reflections on
>Trusting Trust" (from Communication of the ACM, Vol. 27, No. 8, August
>1984, pp. 761-763).

Note that the one he presents won't fit on one line.

But you can just take out the line breaks to get everything but the
preprocessor directives on one line, and most implementations let you
invoke the preprocessor separately to get a (nonportable) program that
can have all the line breaks removed and still be valid...

dave
('twill be a long line though)

--
Dave Vandervies
So you consider it a lie to express an opinion that is supported by facts?
Interesting, and presumably the reason why so many of your opinions are *not*
supported by facts. --Richard Heathfield roasts a troll in comp.lang.c

Dave Vandervies, Mar 16, 2005
7. ### Guest

Dave Vandervies wrote:
> In article <>,
> Roy Hills <> wrote:
> >On 16 Mar 2005 02:23:49 -0800, "Puneet" <>
> >wrote:
> >>Can we write a single line C program whose output is the program
> >>itself?

> >
> >Ken Thompson mentions this in his classic paper "Reflections on
> >Trusting Trust" (from Communication of the ACM, Vol. 27, No. 8,

August
> >1984, pp. 761-763).

>
> Note that the one he presents won't fit on one line.
>
> But you can just take out the line breaks to get everything but the
> preprocessor directives on one line, and most implementations let you
> invoke the preprocessor separately to get a (nonportable) program

that
> can have all the line breaks removed and still be valid...
>
>
> dave
> ('twill be a long line though)

Does the OP mean output the source of the program, or output the
program though?

, Mar 16, 2005
8. ### Kevin D. QuittGuest

On 16 Mar 2005 02:23:49 -0800, "Puneet" <> wrote:
>Can we write a single line C program whose output is the program
>itself?

Some of we can. It's not proper C or portable. With 2 lines, it can be.

--
#include <standard.disclaimer>
_
Kevin D Quitt USA 91387-4454 96.37% of all statistics are made up
Per the FCA, this address may not be added to any commercial mail list

Kevin D. Quitt, Mar 16, 2005
9. ### Arthur J. O'DwyerGuest

[OT] Re: write a single line C program whose output is the program itself

On Wed, 16 Mar 2005 wrote:
>> Roy Hills <> wrote:
>>> "Puneet" <> wrote:
>>>> Can we write a single line C program whose output is the program
>>>> itself?
>>>
>>> Ken Thompson mentions this in his classic paper "Reflections on
>>> Trusting Trust" (from Communication of the ACM, Vol. 27, No. 8,
>>> August 1984, pp. 761-763).

> Does the OP mean output the source of the program, or output the
> program though?

If you think there's a quantitative difference, then you haven't
been programming long enough.

-Arthur

Arthur J. O'Dwyer, Mar 16, 2005
10. ### Daniel VallstromGuest

Kevin D. Quitt wrote:
> On 16 Mar 2005 02:23:49 -0800, "Puneet" <>

wrote:
> >Can we write a single line C program whose output is the program
> >itself?

>
> Some of we can. It's not proper C or portable. With 2 lines, it can

be.

$gcc -std=c99 -Wall -W -pedantic -O fixpointOneLine.c$ ./a.out
int printf(const char*s,...);char*p="\\int printf(const
char*s,...);char*p=%c%c%s%c,n='%cn',q='%c',*m=%c%s%c;%s%c",n='\n',q='"',*m="int
main(){return!printf(p+1,q,*p,p,q,*p,q,q,m,q,m,n);}";int
main(){return!printf(p+1,q,*p,p,q,*p,q,q,m,q,m,n);}
$./a.out | diff - fixpointOneLine.c$ wc fixpointOneLine.c
1 7 245 fixpointOneLine.c

Daniel Vallstrom

Daniel Vallstrom, Mar 16, 2005
11. ### PuneetGuest

Hello All,

Thanx for taking the question seriously.

i clear the question is can we write a code which prints the program
itself. means whatever code we written, in output it showz the whole
program. But code should be in one line.

Puneet

Puneet, Mar 17, 2005
12. ### Kevin D. QuittGuest

On 17 Mar 2005 04:59:26 -0800, "Puneet" <> wrote:
>Thanx for taking the question seriously.

Right. Did you try compiling the gibberish he posted?

--
#include <standard.disclaimer>
_
Kevin D Quitt USA 91387-4454 96.37% of all statistics are made up
Per the FCA, this address may not be added to any commercial mail list

Kevin D. Quitt, Mar 17, 2005
13. ### Mark McIntyreGuest

On 17 Mar 2005 04:59:26 -0800, in comp.lang.c , "Puneet"
<> wrote:

>i clear the question is can we write a code which prints the program
>itself. means whatever code we written, in output it showz the whole
>program.

Its called a quine and a websearch will find plenty.

>But code should be in one line.

thats easy. Linebreaks are irrelevant to C, they're just more whitespace.

ps its spelt shows not showz

--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>

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Mark McIntyre, Mar 17, 2005
14. ### Peter NilssonGuest

Mark McIntyre wrote:
> ...Linebreaks are irrelevant to C, they're just more whitespace.

They are relevant to preprocessing in general, but particularly
to directives.

--
Peter

Peter Nilsson, Mar 18, 2005
15. ### Mark McIntyreGuest

Re: [OT] Re: write a single line C program whose output is the program itself

On Wed, 16 Mar 2005 15:00:57 -0500 (EST), in comp.lang.c , "Arthur J. O'Dwyer"
<> wrote:

>
>On Wed, 16 Mar 2005 wrote:
>>> Roy Hills <> wrote:
>>> Does the OP mean output the source of the program, or output the

>> program though?

>
> If you think there's a quantitative difference, then you haven't
>been programming long enough.

Hmm. There's no difference between outputting the source, and outputting the
machine code.... ?

--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>

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Mark McIntyre, Mar 18, 2005
16. ### Daniel VallstromGuest

Puneet wrote:
> i clear the question is can we write a code which prints the program
> itself. means whatever code we written, in output it showz the whole
> program. But code should be in one line.

The very post you replied to contains a one line quine which does what
you want! Here is a repost of the program (meant to be on one line):

int printf(const char*s,...);char*p="\\int printf(const
char*s,...);char*p=%c%c%s%c,n='%cn',q='%c',*m=%c%s%c;%s%c",n='\n',q='"',*m="int
main(){return!printf(p+1,q,*p,p,q,*p,q,q,m,q,m,n);}";int
main(){return!printf(p+1,q,*p,p,q,*p,q,q,m,q,m,n);}

Daniel Vallstrom

Daniel Vallstrom, Mar 20, 2005
17. ### Daniel VallstromGuest

Peter Nilsson wrote:
> Mark McIntyre wrote:
> > ...Linebreaks are irrelevant to C, they're just more whitespace.

>
> They are relevant to preprocessing in general, but particularly
> to directives.

More to the point they affect any solution to the problem at hand.

Daniel Vallstrom

Daniel Vallstrom, Mar 20, 2005