custom printf() function

[sam_cit]

Hi Everyone,

I have the following custom printf() function in the my program unit
and when i execute the program, the actual printf() function is invoked
and i get no error, no warning. However when i rename printf to printf1
in the following program unit, it invokes my custom function... what
makes this happen?

int printf(char* p,int a)
{
return(0);
}

int main()
{
struct sample
{
int a;
}a,*b;
b = &a;
b->a = 5;
++(*b).a;
printf("%d\n",b->a);
}

[Kenny McCormack]

In article <11************ **********@38g2 000cwa.googlegr oups.com>,
<sa*****@yahoo. co.inwrote:

>Hi Everyone,

I have the following custom printf() function in the my program unit
and when i execute the program, the actual printf() function is invoked
and i get no error, no warning. However when i rename printf to printf1
in the following program unit, it invokes my custom function... what
makes this happen?

int printf(char* p,int a)
{

puts("Here we are"); /* Add this line */

> return(0);
}

int main()
{
struct sample
{
int a;
}a,*b;
b = &a;
b->a = 5;
++(*b).a;
printf("%d\n",b->a);
}

The droids will tell you that you can't invade the implementation name
space, and that, alas, printf is in that name space.

When I took your program and added the line shown above, gcc compiled it
and ran it OK (but, quite correctly, generated the following warning:

x.c:2: warning: conflicting types for built-in function `printf'

But it will work correctly on most implementations anyway.

[sam_cit]

When I took your program and added the line shown above, gcc compiled it

and ran it OK (but, quite correctly, generated the following warning:

x.c:2: warning: conflicting types for built-in function `printf'

But it will work correctly on most implementations anyway.

What exactly do you mean by correctly? are you saying it would invoke
the actual printf() function or the the customized printf() function?

[websnarf]

sam_...@yahoo.c o.in wrote:

When I took your program and added the line shown above, gcc compiled it
and ran it OK (but, quite correctly, generated the following warning:

x.c:2: warning: conflicting types for built-in function `printf'

But it will work correctly on most implementations anyway.

What exactly do you mean by correctly? are you saying it would invoke
the actual printf() function or the the customized printf() function?

I think it typically depends on the compiler and mode it is compiled
in. For example, some compilers generate "in-line" calls for built-in,
and standard library functions, depending on the flags it is given.
Because you can always compile modules seperately, there is no way for
the compiler to know that you have overridden a built-in function until
after it has emitted its code. Most compilers will nevertheless take
your overridden definition so long as you make sure the flags its given
tell it not to generate inline code for intrinsics.

--
Paul Hsieh
http://www.pobox.com/~qed/
http://bstring.sf.net/

[Richard Heathfield]

sa*****@yahoo.c o.in said:

Hi Everyone,

I have the following custom printf() function in the my program unit
and when i execute the program, the actual printf() function is invoked
and i get no error, no warning. However when i rename printf to printf1
in the following program unit, it invokes my custom function... what
makes this happen?

Undefined behaviour makes this (or something else, or nothing) happen.

If you stick to the rules, so does C. If you break the rules, C is free to
break them too. You don't want that to happen.

Key learning point: Don't Break The Rules.

One of the rules is: don't tread on the implementation.

Naming a function 'printf' constitutes treading on the implementation.

So Don't Do That.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at the above domain, - www.

[Keith Thompson]

sa*****@yahoo.c o.in writes:

>When I took your program and added the line shown above, gcc compiled it
and ran it OK (but, quite correctly, generated the following warning:

x.c:2: warning: conflicting types for built-in function `printf'

But it will work correctly on most implementations anyway.

What exactly do you mean by correctly? are you saying it would invoke
the actual printf() function or the the customized printf() function?

Neither behavior is either correct or incorrect.

The standard says:

All identifiers with external linkage in any of the following
subclauses (including the future library directions) are always
reserved for use as identifiers with external linkage.

The phrase "the following subclauses" refers to the descriptions of
the standard headers, including <stdio.hwhich declares printf().

You *could* declare your printf as static.

Or, better yet, don't try to use the name "printf" for anything other
than the standard function of that name, unless your goal is to
confuse anyone reading your code.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Kenny McCormack]

In article <ln************ @nuthaus.mib.or g>,
the totally psychotic Keith Thompson <ks***@mib.orgw rote:

>sa*****@yahoo. co.in writes:

>>When I took your program and added the line shown above, gcc compiled it
and ran it OK (but, quite correctly, generated the following warning:

x.c:2: warning: conflicting types for built-in function `printf'

But it will work correctly on most implementations anyway.

What exactly do you mean by correctly? are you saying it would invoke
the actual printf() function or the the customized printf() function?

Neither behavior is either correct or incorrect.

I think I already granted (in the part you snipped, as they say) that
the droids (that's you, in case you're wondering) would say that it is
undefined, blah, blah, blah.

[Franchie]

On Jan 14, 12:30 am, gaze...@xmissio n.xmission.com (Kenny McCormack)
wrote:

x.c:2: warning: conflicting types for built-in function `printf'

or perhaps more simply, use a #define:

int custom_printf(c har *in, ...) {XXX}
#define printf custom_printf

This way, there will be no 'conflicting types', and there will never be
any doubt as to which function is called, and it will look exactly like
the 'normal' printf...
You can then choose to enable it or not without having to change your
code, etc.

F.

[santosh]

Franchie wrote:

On Jan 14, 12:30 am, gaze...@xmissio n.xmission.com (Kenny McCormack)
wrote:

x.c:2: warning: conflicting types for built-in function `printf'

or perhaps more simply, use a #define:

int custom_printf(c har *in, ...) {XXX}
#define printf custom_printf

This way, there will be no 'conflicting types', and there will never be
any doubt as to which function is called, and it will look exactly like
the 'normal' printf...
You can then choose to enable it or not without having to change your
code, etc.

F.

Your attribution is incorrect. "Kenny McCormack" did not write what
you've attributed to him above.

[Kenny McCormack]

In article <11************ *********@51g20 00cwl.googlegro ups.com>,
Franchie <Fr************ ******@gmail.co mwrote:
....

>Disclaimer: I did not intend this quote as a statement. Simply, it was
the result of the compilation of using duplicate printfs, and seemed an
appropriate starting-point for the post. No comment intended, I hope no
offense taken.

Don't worry about it. Anyone with two brain cells to run together could
figure it out.

Admittedly, that lets out most of the droids of this ng, but, really,
when you get down to it, do you care about those fuckwits?