sizeof

[pnreddy1976@gmail.com]

Hi,
How can we write a function, which functionality is similar to sizeof
function
any one send me source code
Reddy

[Richard Heathfield]

Re: sizeof

pnreddy1976@gma il.com said:
[color=blue]
> Hi,
> How can we write a function, which functionality is similar to sizeof
> function[/color]

We can't, because sizeof is not a function. (And there's a good reason why
it's not a function.)

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

[Madhav]

Re: sizeof

Richard Heathfield wrote:[color=blue]
> pnreddy1976@gma il.com said:
>[color=green]
> > Hi,
> > How can we write a function, which functionality is similar to sizeof
> > function[/color]
>
> We can't, because sizeof is not a function. (And there's a good reason why
> it's not a function.[/color]

Can you tell us that reason, Richard?

Regards,
Madhav.

[Richard Heathfield]

Re: sizeof

Madhav said:
[color=blue]
> Richard Heathfield wrote:[color=green]
>> pnreddy1976@gma il.com said:
>>[color=darkred]
>> > Hi,
>> > How can we write a function, which functionality is similar to sizeof
>> > function[/color]
>>
>> We can't, because sizeof is not a function. (And there's a good reason
>> why it's not a function.[/color]
>
> Can you tell us that reason, Richard?[/color]

Spend a little time trying to write such a function, and you'll discover it
for yourself quickly enough. Hint: what type should its parameter be?

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

[Xicheng Jia]

Re: sizeof

pnreddy1976@gma il.com wrote:[color=blue]
> Hi,
> How can we write a function, which functionality is similar to sizeof
> function
> any one send me source code[/color]

the problem is that the result of sizeof() is interpolated at compile
time. Can any function do it that way! :-)

Xicheng

[Malcolm]

Re: sizeof




"Xicheng Jia" <xicheng@gmail. com> wrote in message[color=blue]
> pnreddy1976@gma il.com wrote:[color=green]
>> Hi,
>> How can we write a function, which functionality is similar to sizeof
>> function
>> any one send me source code[/color]
>
> the problem is that the result of sizeof() is interpolated at compile
> time. Can any function do it that way! :-)
>[/color]
A compiler is permitted to inline functions, and then to simplify code. A
really good compiler might simplify constructs like acos(0) to produce half
PI, but this is rare.
--
Buy my book 12 Common Atheist Arguments (refuted)
$1.25 download or $7.20 paper, available www.lulu.com/bgy1mm

[Frederick Gotham]

Re: sizeof

Xicheng Jia posted:
[color=blue]
> Can any function do it that way! :-)[/color]


A macro function perhaps:


#define SizeOf(Type) \
( \
(const char*)128 - \
\
(const char*)( (const Type*)128 - 1 ) \
)


--

Frederick Gotham

[lovecreatesbeauty]

Re: sizeof


Richard Heathfield wrote:[color=blue]
> Spend a little time trying to write such a function, and you'll discover it
> for yourself quickly enough. Hint: what type should its parameter be?[/color]

I think it is because we need C language to tell us the sizes of
various types and objects by sizeof. It's the purpose of sizeof itself
and why it is called the name operator. We have no alternative choice.

lovecreatesbeau ty

[Marc Thrun]

Re: sizeof

Frederick Gotham schrieb:[color=blue]
> Xicheng Jia posted:
>[color=green]
>> Can any function do it that way! :-)[/color]
>
>
> A macro function perhaps:
>
>
> #define SizeOf(Type) \
> ( \
> (const char*)128 - \
> \
> (const char*)( (const Type*)128 - 1 ) \
> )
>
>[/color]

Undefined behaviour - your pointer most likely does not point to any
valid object. And even if it does on certain implementations , it makes
no sense in c.l.c as conversion from integer to pointer types is
implementation defined and thus not portable.

--
Marc Thrun

http://www.tekwarrior.de/

[Frederick Gotham]

Re: sizeof

Marc Thrun posted:
[color=blue]
> Frederick Gotham schrieb:[color=green]
>> Xicheng Jia posted:
>>[color=darkred]
>>> Can any function do it that way! :-)[/color]
>>
>>
>> A macro function perhaps:
>>
>>
>> #define SizeOf(Type) \
>> ( \
>> (const char*)128 - \
>> \
>> (const char*)( (const Type*)128 - 1 ) \
>> )
>>
>>[/color]
>
> Undefined behaviour - your pointer most likely does not point to any
> valid object. And even if it does on certain implementations , it makes
> no sense in c.l.c as conversion from integer to pointer types is
> implementation defined and thus not portable.[/color]


Yes I'm aware of that.

This thread isn't about anything serious; it's more of a little mind game
to see who can write a "sizeof".


--

Frederick Gotham

[Andrew Poelstra]

Re: sizeof

On 2006-06-18, Xicheng Jia <xicheng@gmail. com> wrote:[color=blue]
> pnreddy1976@gma il.com wrote:[color=green]
>> Hi,
>> How can we write a function, which functionality is similar to sizeof
>> function
>> any one send me source code[/color]
>
> the problem is that the result of sizeof() is interpolated at compile
> time. Can any function do it that way! :-)
>[/color]

Yes, any standard function could do it that way; the compiler has control
over all the libraries included with it. Not only that, but with C99 VLA's,
sizeof /cannot/ be computer at compile time in some cases.

--
Andrew Poelstra < http://www.wpsoftware.net/blog >
To email me, use "apoelstra" at the above address.
I know that area of town like the back of my head.

[ada]

Re: sizeof

Andrew Poelstra <apoelstra@loca lhost.localdoma in> writes:
[color=blue]
> On 2006-06-18, Xicheng Jia <xicheng@gmail. com> wrote:[color=green]
>> pnreddy1976@gma il.com wrote:[color=darkred]
>>> Hi,
>>> How can we write a function, which functionality is similar to sizeof
>>> function
>>> any one send me source code[/color]
>>
>> the problem is that the result of sizeof() is interpolated at compile
>> time. Can any function do it that way! :-)
>>[/color]
>
> Yes, any standard function could do it that way; the compiler has control
> over all the libraries included with it. Not only that, but with C99 VLA's,
> sizeof /cannot/ be computer at compile time in some cases.[/color]
Why?[color=blue]
>
> --
> Andrew Poelstra < http://www.wpsoftware.net/blog >
> To email me, use "apoelstra" at the above address.
> I know that area of town like the back of my head.[/color]

[Xicheng Jia]

Re: sizeof

Andrew Poelstra wrote:[color=blue]
> On 2006-06-18, Xicheng Jia <xicheng@gmail. com> wrote:[color=green]
> > pnreddy1976@gma il.com wrote:[color=darkred]
> >> Hi,
> >> How can we write a function, which functionality is similar to sizeof
> >> function
> >> any one send me source code[/color]
> >
> > the problem is that the result of sizeof() is interpolated at compile
> > time. Can any function do it that way! :-)
> >[/color]
>
> Yes, any standard function could do it that way; the compiler has control
> over all the libraries included with it. Not only that, but with C99 VLA's,
> sizeof /cannot/ be computer at compile time in some cases.
>[/color]

Sorry, I should have said that the operand of sizeof() is interpolated
at compile-time. so i++ in sizeof(i++) does not increment i and the
following code prints 'i = 1' instead of 'i = 2'..

#include<stdio. h>
int main()
{
int i = 1, sz;
sz = sizeof(i++);
printf("i = %d\n", i);
return 0;
}

In ISO C, Macro is a different thing from function. and I am not sure
if inline function can do things like sizeof() does though . any hints
about this, thanks..:)

Xicheng

[Keith Thompson]

Re: sizeof

pnreddy1976@gma il.com writes:[color=blue]
> How can we write a function, which functionality is similar to sizeof
> function[/color]

Why would you want to do that?
[color=blue]
> any one send me source code[/color]

Nope.

The only plausible reason to do something like this is as a homework
assignment (though it's a particularly bad one). If this is the case
here, we're certainly not going to do your homework for you.

If you have some other reason, tell us what it is. Tell us what
you're *really* trying to accomplish, and we might be able to help you
find a better solution. (Based on your question, a better solution is
obvious: use the sizeof operator, that's what it's for.)

--
Keith Thompson (The_Other_Keit h) kst-u@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.

[Richard Heathfield]

Re: sizeof

ada said:
[color=blue]
> Andrew Poelstra <apoelstra@loca lhost.localdoma in> writes:[/color]

<snip>
[color=blue][color=green]
>> Not only that, but with C99
>> VLA's, sizeof /cannot/ be computer at compile time in some cases.[/color]
> Why?[/color]

Here's one reason:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
puts("How many array elements would you like?");
char buf[32];
if(fgets(buf, sizeof buf, stdin) != NULL)
{
unsigned long n = strtoul(buf, NULL, 10);
if(n > 0)
{
int arr[n];
/* ... */

There is simply no way that the compiler can know at compile time how many
elements the user will ask for at run time.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)