function call in conditional operator?

[bnp]

Hi,

Is possible to use functions in conditional operator as ashown below.
.....
.....
int fun1()
{
// body
}

int fun2()
{
//body
}

....
main()
{...
int x;
x = (a>b)?fun1():fun2();
}

[Régis Troadec]

"bnp" <bh**********@yahoo.com> a écrit dans le message de
news:7d*************************@posting.google.co m...

Hi,
Hi,
Is possible to use functions in conditional operator as ashown below.
....
....
int fun1()
{
// body
}

int fun2()
{
//body
}

...
main()
{...
int x;
x = (a>b)?fun1():fun2();

Yes,

it's semantically equivalent to:

if (a>b)
x = fun1();
else
x = fun2();

IMHO, I find that the conditional operator fits very well in this case.

Regis

[Kevin Bracey]

In message <7d*************************@posting.google.com>
bh**********@yahoo.com (bnp) wrote:

Hi,

Is possible to use functions in conditional operator as ashown below. x = (a>b)?fun1():fun2();

Yes. And even more entertainingly, you can do this:

x = (a > b ? fun1 : fun2) (c, d, e);

--
Kevin Bracey, Principal Software Engineer
Tematic Ltd Tel: [phone]
182-190 Newmarket Road Fax: [phone]
Cambridge, CB5 8HE, United Kingdom WWW: http://www.tematic.com/

[Case]

Kevin Bracey wrote:

Yes. And even more entertainingly, you can do this:

x = (a > b ? fun1 : fun2) (c, d, e);

Yes, of course! Never thought of stretching the meaning
of a function 'pointer' this far. Things like 5["Hello world"]
(as you know I'm sure) are entertaining too.

Kees

[Paul D. Boyle]

Kevin Bracey <ke**********@tematic.com> wrote:
: In message <7d*************************@posting.google.com>
: bh**********@yahoo.com (bnp) wrote:

:> Hi,
:>
:> Is possible to use functions in conditional operator as ashown below.

:> x = (a>b)?fun1():fun2();

: Yes. And even more entertainingly, you can do this:

: x = (a > b ? fun1 : fun2) (c, d, e);

Are you saying that if functions 'fun1' and 'fun2' have the same
prototypes and take (appropriately typed) arguments, 'c', 'd', and 'e',
that this would be equivalent to:

if ( a > b )
x = fun1( c, d, e );
else
x = fun2( c, d, e );

?

Paul

--
Paul D. Boyle
bo***@laue.chem.ncsu.edu
North Carolina State University
http://www.xray.ncsu.edu

[Case]

Kevin Bracey wrote:

Yes. And even more entertainingly, you can do this:

x = (a > b ? fun1 : fun2) (c, d, e);

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

Case

[Eric Sosman]

bnp wrote:

Hi,

Is possible to use functions in conditional operator as ashown below.
....
....
int fun1()
{
// body
}

int fun2()
{
//body
}

...
main()
{...
int x;
x = (a>b)?fun1():fun2();
}

Yes. You can even use `x = (a > b ? fun1 : fun2)();'
if you have sado-masochistic tendencies.

--
Er*********@sun.com

[Case]

Case wrote:

Kevin Bracey wrote:

Yes. And even more entertainingly, you can do this:

x = (a > b ? fun1 : fun2) (c, d, e);

BTW what other seemingly strange standard C constructions
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people

About the whole human race of course. But I meant C
programmers. :-)

Kees

[glen herrmannsfeldt]

bnp wrote:

(snip)

Is possible to use functions in conditional operator as ashown below.
(snip)
int x;
x = (a>b)?fun1():fun2();

Not only that, you can even do

x=(a>b?fun1:fun2)();

assuming that fun1 and fun2 are declared as functions.
(It is more interesting if they have arguments.)
-- glen

[pete]

Paul D. Boyle wrote:

Kevin Bracey <ke**********@tematic.com> wrote:
: In message <7d*************************@posting.google.com>
: bh**********@yahoo.com (bnp) wrote:

:> Hi,
:>
:> Is possible to use functions in conditional operator as ashown below.

:> x = (a>b)?fun1():fun2();

: Yes. And even more entertainingly, you can do this:

: x = (a > b ? fun1 : fun2) (c, d, e);

Are you saying that if functions 'fun1' and 'fun2' have the same
prototypes and take (appropriately typed) arguments, 'c', 'd', and
'e',

It could happen. Take a look at this line of code

string = (digit == 0 ? sput_ip1 : sput_i)(integer / 10, string);

from

http://groups.google.com/groups?selm...mindspring.com

sput_ip1 and sput_i, are functions.

--
pete

[Keith Thompson]

Case <[e-mail]> writes:

Kevin Bracey wrote:

Yes. And even more entertainingly, you can do this:
x = (a > b ? fun1 : fun2) (c, d, e);

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

Google "Duff's Device".

You might also take a look at the past winners of the International
Obfuscated C Code Contest (google "IOCCC"). Please keep firmly in
mind that some of the earlier winners are non-portable, and that
*none* of them are examples of good C code (except for extremely and
deliberately perverse values of "good").

--
Keith Thompson (The_Other_Keith) 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.

[Chris Dollin]

Case wrote:

Kevin Bracey wrote:

Yes. And even more entertainingly, you can do this:

x = (a > b ? fun1 : fun2) (c, d, e);

Yes, of course! Never thought of stretching the meaning
of a function 'pointer' this far.

That's hardly "stretching", more a "perfectly routine use".

[And people think the Sapir-Whorf hypothesis is false ...]

--
Chris "f(x) := E means updater(f)(x)(E)" Dollin
C FAQs at: http://www.faqs.org/faqs/by-newsgrou...mp.lang.c.html
C welcome: http://www.angelfire.com/ms3/bchambl...me_to_clc.html

[August Derleth]

On Mon, 17 May 2004 18:40:49 +0000, glen herrmannsfeldt wrote:

bnp wrote:

(snip)

Is possible to use functions in conditional operator as ashown below.

(snip)

int x;
x = (a>b)?fun1():fun2();

Not only that, you can even do

x=(a>b?fun1:fun2)();

Yes, that is possible, now that I think of it. It could even be a rather
elegant solution to a problem.

It will, however, leave the wet-behind-the-ears maintenance programmer who
was raised on Java and Visual Basic scratching his head, as well as
sparking a Holy War with those who still believe in Structured Programming. ;)

--
yvoregnevna gjragl-guerr gjb-gubhfnaq guerr ng lnubb qbg pbz
To email me, rot13 and convert spelled-out numbers to numeric form.
"Makes hackers smile" makes hackers smile.

[Case]

Keith Thompson wrote:

Case <[e-mail]> writes:

Kevin Bracey wrote:

Yes. And even more entertainingly, you can do this:
x = (a > b ? fun1 : fun2) (c, d, e);

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

Google "Duff's Device".

This one is really amazing! Thanks.

You might also take a look at the past winners of the International
Obfuscated C Code Contest (google "IOCCC"). Please keep firmly in
mind that some of the earlier winners are non-portable, and that
*none* of them are examples of good C code (except for extremely and
deliberately perverse values of "good").

I know IOCCC and own the book "Obfuscated C and Other Mysteries" by Don
Libes. That's real fun too indeed.

Kees

[Joona I Palaste]

August Derleth <se*@sig.now> scribbled the following:

On Mon, 17 May 2004 18:40:49 +0000, glen herrmannsfeldt wrote:

Not only that, you can even do

x=(a>b?fun1:fun2)();

Yes, that is possible, now that I think of it. It could even be a rather
elegant solution to a problem. It will, however, leave the wet-behind-the-ears maintenance programmer who
was raised on Java and Visual Basic scratching his head, as well as
sparking a Holy War with those who still believe in Structured Programming. ;)

It's not so much a feature of C as a feature of first-class functions.
In other languages, like ML or Haskell, you can even manufacture new
functions at run-time and then call them.

For example:
mynewfunction :: int -> (int -> int)
mynewfunction x = \y.(x+y)

When called, for example, with an argument of 5, this function returns
a function that adds 5 to its argument. Can you do this in C?

It wouldn't be too much trouble, semantically, to add method references
to Java. How it's handled down at the implemenation level is anyone's
guess, though.

--
/-- Joona Palaste (pa*****@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Nothing lasts forever - so why not destroy it now?"
- Quake

[Dan Pop]

In <7d*************************@posting.google.com> bh**********@yahoo.com (bnp) writes:

Is possible to use functions in conditional operator as ashown below.
....
....
int fun1()
{
// body
}

int fun2()
{
//body
}

...
main()
{...
int x;
x = (a>b)?fun1():fun2();
}

In such cases, the best way of finding the answer is by trying to answer
another question: why not?

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[glen herrmannsfeldt]

August Derleth wrote:

(snip)

x=(a>b?fun1:fun2)();

Yes, that is possible, now that I think of it. It could even be a rather
elegant solution to a problem. It will, however, leave the wet-behind-the-ears maintenance programmer who
was raised on Java and Visual Basic scratching his head, as well as
sparking a Holy War with those who still believe in Structured Programming. ;)

Well, in Java you can do it with Object reference variables.

x=(a>b?string1:string2).equals("hi");

something like:

x=!strcmp((a>b?string1:string2),"hi");

With Java's reflection, you can probably do the equivalent of
function pointers in a conditional expression, though I won't try.

I don't know about VB at all.

-- glen

[Malcolm]

"Case" <[e-mail]> wrote in message

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

C allows a lot of this sort of thing in order to make the compiler's grammar
easier to specify.
The problem is that people then think it is fun to use such constructions in
production code.

[Mitchell]

On Mon, 17 May 2004 18:17:05 +0200, Case <[e-mail]> wrote:

Yes, of course! Never thought of stretching the meaning
of a function 'pointer' this far. Things like 5["Hello world"]
(as you know I'm sure) are entertaining too.

I'm a bit stumped here, how does 5("Hello world"); works?
#define 5(_a) printf("%s",_a) ?

[Joona I Palaste]

Mitchell <ch***************@inahatespamme.cohatespamm> scribbled the following:

On Mon, 17 May 2004 18:17:05 +0200, Case <[e-mail]> wrote:

Yes, of course! Never thought of stretching the meaning
of a function 'pointer' this far. Things like 5["Hello world"]
(as you know I'm sure) are entertaining too.

I'm a bit stumped here, how does 5("Hello world"); works?
#define 5(_a) printf("%s",_a) ?

5("Hello world"); doesn't work. It's 5["Hello world"] with square
brackets instead of normal ones. It works because [] is actually a
commutative operator - a[b] is the exact same thing as b[a].

--
/-- Joona Palaste (pa*****@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/

[kal]

Case <[e-mail]> wrote in message news:<40*********************@news.xs4all.nl>...

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

Why is the resultant deferenced type (char) and not some other
scalar type?

[Richard Bos]

k_*****@yahoo.com (kal) wrote:

Case <[e-mail]> wrote in message news:<40*********************@news.xs4all.nl>...

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

Why is the resultant deferenced type (char) and not some other
scalar type?

Because that's how the Standard defines it. Besides, what other type
would you have it be?

Richard

[Richard Bos]

"Malcolm" <ma*****@55bank.freeserve.co.uk> wrote:

"Case" <[e-mail]> wrote in message

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

C allows a lot of this sort of thing in order to make the compiler's grammar
easier to specify.

Oddly enough, in this case the grammar wouldn't have been much easier if
this were disallowed. "The first expression shall have type 'pointer to
object type', the second expression shall have integral type" wouldn't
have been any simpler than the actual C89 sentence "One of the
expressions shall have type 'pointer to object type', the other
expression shall have integral type". It probably even would've made
compilers (very) slightly smaller.

Richard

[Irrwahn Grausewitz]

Joona I Palaste <pa*****@cc.helsinki.fi> wrote:

Mitchell <ch***************@inahatespamme.cohatespamm> scribbled the following:

On Mon, 17 May 2004 18:17:05 +0200, Case <[e-mail]> wrote:

Yes, of course! Never thought of stretching the meaning
of a function 'pointer' this far. Things like 5["Hello world"]
(as you know I'm sure) are entertaining too.

I'm a bit stumped here, how does 5("Hello world"); works?
#define 5(_a) printf("%s",_a) ?

5("Hello world"); doesn't work. It's 5["Hello world"] with square
brackets instead of normal ones. It works because [] is actually a
commutative operator - a[b] is the exact same thing as b[a].

Or, to put it another way, the array subscript operator [] is
essentially "syntactic sugar" and a[b] is semantically equivalent
to (*((a)+(b))), which in turn obviously equals (*((b)+(a))),
because of the commutative nature of the binary + operator.

Regards
--
Irrwahn Grausewitz (ir*******@freenet.de)
welcome to clc: http://www.ungerhu.com/jxh/clc.welcome.txt
clc faq-list : http://www.faqs.org/faqs/C-faq/faq/
clc OT guide : http://benpfaff.org/writings/clc/off-topic.html

[Dan Pop]

In <a5*************************@posting.google.com> k_*****@yahoo.com (kal) writes:

Case <[e-mail]> wrote in message news:<40*********************@news.xs4all.nl>...

BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

Why is the resultant deferenced type (char) and not some other
scalar type?

Engage your brain and tell us what type can be expected from
"fsdssdfssf"[5]. Then explain why would you expect another type from
5["fsdssdfssf"]. I assume you have already read the FAQ...

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Mabden]

"Case" <[e-mail]> wrote in message
news:40*********************@news.xs4all.nl...

Keith Thompson wrote:

Case <[e-mail]> writes:

Kevin Bracey wrote:

Yes. And even more entertainingly, you can do this:
x = (a > b ? fun1 : fun2) (c, d, e);
BTW what other seemingly strange standard C construction
do you know? I mentioned 5["fsdssdfssf"] which looks
very strange to most people even very experienced C
programmers. It would be fun to discuss this kind of
constructs.

Google "Duff's Device".

This one is really amazing! Thanks.

send(to, from, count)
register short *to, *from;
register count;
{
register n=(count+7)/8;
switch(count%8){
case 0: do{ *to = *from++;
case 7: *to = *from++;
case 6: *to = *from++;
case 5: *to = *from++;
case 4: *to = *from++;
case 3: *to = *from++;
case 2: *to = *from++;
case 1: *to = *from++;
}while(--n>0);
}
}

So basically at some count != 8 you end up with:

} while (--n>0);

And this is legal? What about the } with no opening {?

--
Mabden

[kal]

Da*****@cern.ch (Dan Pop) wrote in message news:<c8**********@sunnews.cern.ch>...

Then explain why would you expect another type from 5["fsdssdfssf"].
Now it seems clear. I got muddled about 'left' and 'right' operands.
But when you phrase it as "one is a pointer type and the other an
integral type" it clarifies itself.
I assume you have already read the FAQ...

Haven't read it. In fact I wasn't planning to read it till I
came across references to it in a few posts. Those references
were direct and pertinent (references to 16.5 etc.) I think one
was yours (Dan Pop) and the names of the posters of the other
two I can't recall at the moment (one was about "if (2 == x) ..."
form.)

When I went and looked at it I was surprised to see how well
done it is. So, I have read SOME of it and am still reading
parts of it almost everday. Thanks for directing me there.

[Dan Pop]

In <3a*****************@newssvr27.news.prodigy.com> "Mabden" <ma****@sbcglobal.net> writes:

send(to, from, count)
register short *to, *from;
register count;
{
register n=(count+7)/8;
switch(count%8){
case 0: do{ *to = *from++;
case 7: *to = *from++;
case 6: *to = *from++;
case 5: *to = *from++;
case 4: *to = *from++;
case 3: *to = *from++;
case 2: *to = *from++;
case 1: *to = *from++;
}while(--n>0);
}
}

So basically at some count != 8 you end up with:

} while (--n>0);

And this is legal? What about the } with no opening {?

Good question. A strict reading of the standard makes it undefined
behaviour. This is not the intent of the authors, but they couldn't be
bothered to get it right.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Kevin Bracey]

In message <c8***********@sunnews.cern.ch>
Da*****@cern.ch (Dan Pop) wrote:

In <3a*****************@newssvr27.news.prodigy.com> "Mabden" <ma****@sbcglobal.net> writes:

And this is legal? What about the } with no opening {?

Good question. A strict reading of the standard makes it undefined
behaviour. This is not the intent of the authors, but they couldn't be
bothered to get it right.

Of course, they're still some way ahead of those who couldn't be bothered to
get involved in authoring it.

--
Kevin Bracey, Principal Software Engineer
Tematic Ltd Tel: [phone]
182-190 Newmarket Road Fax: [phone]
Cambridge, CB5 8HE, United Kingdom WWW: http://www.tematic.com/

[Peter Shaggy Haywood]

Groovy hepcat Mitchell was jivin' on Wed, 19 May 2004 11:07:08 +0800
in comp.lang.c.
Re: function call in conditional operator?'s a cool scene! Dig it!

On Mon, 17 May 2004 18:17:05 +0200, Case <[e-mail]> wrote:

Yes, of course! Never thought of stretching the meaning
of a function 'pointer' this far. Things like 5["Hello world"]
(as you know I'm sure) are entertaining too.

I'm a bit stumped here, how does 5("Hello world"); works?

It doesn't. But 5["Hello world"] does. It works like this:

1) "Hello world" is somewhat equivalent to

char somestring[] = {'H', 'e', 'l', 'l', 'o', ' ',
'w', 'o', 'r', 'l', 'd'};

2) In an expression, "Hello world"[5] is therefore somewhat equivalent
to somestring[5].

3) This is equivalent to *(somestring + 5).

4) That is equivalent to *(5 + somestring).

6) And that is equivalent to 5[somestring].

7) So, that is somewhat equivalent to 5["Hello world"].

Understand?

--

Dig the even newer still, yet more improved, sig!

http://alphalink.com.au/~phaywood/
"Ain't I'm a dog?" - Ronny Self, Ain't I'm a Dog, written by G. Sherry & W. Walker.
I know it's not "technically correct" English; but since when was rock & roll "technically correct"?

[Ralmin]

"glen herrmannsfeldt" <ga*@ugcs.caltech.edu> wrote:

Well, in Java you can do it with Object reference variables.

x=(a>b?string1:string2).equals("hi");

The concept works on C too, except that it's messy to include a reference to
the object as part of the method's arguments.

#include <string.h>

struct string {
int (*equals)(struct string *, const char *);
char *data;
};

int str_equals(struct string *this, const char *other)
{
return !strcmp(this->data, other);
}

int main(void)
{
struct string string1 = {str_equals, "Hello"};
struct string string2 = {str_equals, "World"};
int x, a = 1, b = 2;
x = ((a > b) ? string1 : string2).equals(((a > b) ? &string1 : &string2),
"hi");
return 0;
}

--
Simon.