const function() !!??

[Sundar]

Do we have something called a const function ? I thought applying the
'const' specifier to a function is meaningless... but when i tried
defining a const function it worked !!
like...
const int func(int a)
{
int b;
.....
return b;
}

...The above code gave no compilation errors ! :->
How should i interpret it ?
(i used MS- vc++ compiler)

Sundar

[dandelion]

"Sundar" <su**********@y ahoo.com> wrote in message
news:9e******** *************** ***@posting.goo gle.com...

<snip>

const int func(int a)
{
int b;
.....
return b;
}

...The above code gave no compilation errors ! :->
And it shouldn't.
How should i interpret it ?

A function returning a const int, that is an non-modifyable integer.

[Emmanuel Delahaye]

Sundar wrote on 30/12/04 :

Do we have something called a const function ? I thought applying the
No.
'const' specifier to a function is meaningless... defining a const function it worked !!
like...
const int func(int a)
{
int b;
.....
return b;
}

That 'const' is useless.

This one is useful:

char const *get_ver (void)
{
return "1.2";
}

--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html
The C-library: http://www.dinkumware.com/refxc.html

"Clearly your code does not meet the original spec."
"You are sentenced to 30 lashes with a wet noodle."
-- Jerry Coffin in a.l.c.c++

[Andrey Tarasevich]

Sundar wrote:

Do we have something called a const function ? I thought applying the
'const' specifier to a function is meaningless...
You can't apply the 'const' specifier to a function in C. That would be
a syntax error.
but when i tried
defining a const function it worked !!
like...
const int func(int a)
{
int b;
.....
return b;
}

This is not a 'const' function. In accordance with C syntax, this
'const' qualifier is applied to the return type of the function. I.e.
this function return type is 'const int'.

Syntactically, a naive attempt to apply a 'const' qualifier to a
function would look as follows

int (const func)(int a)

but this simply won't compile.

--
Best regards,
Andrey Tarasevich

[Keith Thompson]

"dandelion" <da*******@mead ow.net> writes:

"Sundar" <su**********@y ahoo.com> wrote in message
news:9e******** *************** ***@posting.goo gle.com...

<snip>

const int func(int a)
{
int b;
.....
return b;
}

...The above code gave no compilation errors ! :->

And it shouldn't.

How should i interpret it ?

A function returning a const int, that is an non-modifyable integer.

But you can't modify the result of a function anyway.

Is there any context in which there's a difference between
const int func(int a) { /* blah blah */ }
and
int func(int a) { /* blah blah */ }
?

As far as I can tell there isn't, and gcc warns:

tmp.c:3: warning: type qualifiers ignored on function return type

I suppose pointers to the two function types would be incompatible,
but I can't think of any other difference.

Probably it was just easier to allow it in the language definition,
even though it's meaningless, than to disallow it.

--
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.

[__MMS__]

Thanks !
I understand 'const' function is meaningless, but please tell me why to
use a 'const' as return type ?!

[Raymond Martineau]

On 2 Jan 2005 00:45:30 -0800, "__MMS__" <su**********@y ahoo.com> wrote:

Thanks !
I understand 'const' function is meaningless, but please tell me why to
use a 'const' as return type ?!

Because the return value of the function would result in undefined
behaviour if it were changed (e.g. returning a string literal).

[Stephen Sprunk]

"__MMS__" <su**********@y ahoo.com> wrote in message
news:11******** **************@ z14g2000cwz.goo glegroups.com.. .

Thanks !
I understand 'const' function is meaningless, but please tell me why to
use a 'const' as return type ?!

You may want to return a const pointer because you don't want the pointed-to
object to be changed.

S

--
Stephen Sprunk "Stupid people surround themselves with smart
CCIE #3723 people. Smart people surround themselves with
K5SSS smart people who disagree with them." --Aaron Sorkin

[Keith Thompson]

"Stephen Sprunk" <st*****@sprunk .org> writes:

"__MMS__" <su**********@y ahoo.com> wrote in message
news:11******** **************@ z14g2000cwz.goo glegroups.com.. .

Thanks !
I understand 'const' function is meaningless, but please tell me why to
use a 'const' as return type ?!

You may want to return a const pointer because you don't want the pointed-to
object to be changed.

That's a good reason for returning a pointer-to-const-whatever, but I
think the OP was asking why you would want to return a const-whatever
(where "whatever" itself may or may not be a pointer type). As far as
I can tell, there's no reason to do so.

--
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.

[Andrey Tarasevich]

__MMS__ wrote:

...
I understand 'const' function is meaningless, but please tell me why to
use a 'const' as return type ?!
...

There's absolutely no point in doing it in C. Values returned by
functions are rvalues. Const-qualification has no effect on rvalues in C
(in C++ things are different, but that's offtopic here).

--
Best regards,
Andrey Tarasevich