sizeof dataTypes at run time

[Raman]

Hi All,

Is ut possible to calculate size of any standard data types at run
time i.e without using sizeof() operator

Thanks and Regards,
Raman

[Jack Klein]

On 26 Mar 2007 04:43:28 -0700, "ja*******@gmai l.com"
<ja*******@gmai l.comwrote in comp.lang.c:

On Mar 26, 10:54 am, "Raman" <ramanchalo...@ gmail.comwrote:

Hi All,

Is ut possible to calculate size of any standard data types at run
time i.e without using sizeof() operator

Thanks and Regards,
Raman

Hi All,

U can get a sizeof any variable without even knowing what is its type
or where it is used. The way is explained below as an example.

U doesn't post here anymore, we killed him.

int a;
printf("size of variable is %d\n",(&a+1)-(&a));

The printf() call above produces undefined behavior on systems where
the underlying type of ptrdiff_t is wider than int. Many such systems
exist.

This is applicable for all datatypes(even for array).

Regards
jamsheed m(ja*******@gma il.com)

--
Jack Klein
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[CBFalconer]

"ja*******@gmai l.com" wrote:

>

.... snip ...

>
U can get a sizeof any variable without even knowing what is its
type or where it is used. The way is explained below as an example.

int a;
printf("size of variable is %d\n",(&a+1)-(&a));

This is applicable for all datatypes(even for array).

U doesn't read this newsgroup any more, and even if he did, he
would be ill-advised to take your advice, which involves undefined
and implementation defined behaviour. I am NOT referring to the
missing includes.

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>

--
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[CBFalconer]

Raman wrote:

>
Is ut possible to calculate size of any standard data types at
run time i.e without using sizeof() operator

Maybe this should be in the FAQ under the heading 'Foolish
Questions'?

--
Chuck F (cbfalconer at maineline dot net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net>
--
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[jamsheedm]

On Mar 26, 4:53 pm, Richard Heathfield <[e-mail].i nvalidwrote:

jamshe...@gmail .com said:

U can get a sizeof any variable without even knowing what is its type
or where it is used. The way is explained below as an example.

int a;
printf("size of variable is %d\n",(&a+1)-(&a));

This is applicable for all datatypes(even for array).

Wrong wrong wrong wrong wrong, as you'd know if you'd tried the above
code yourself.

The correct answer, always, is: use sizeof. That is what it is *for*.

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

its possible
printf("size of variable is %d\n",(char*)(& a+1)-(char*)(&a));
This will print the proper size of variable.

[Richard Heathfield]

ja*******@gmail .com said:

<snip>

printf("size of variable is %d\n",(char*)(& a+1)-(char*)(&a));
This will print the proper size of variable.

He didn't ask for the size of a variable, but for the size of a type.
Check the subject line: "sizeof dataTypes at run time".

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

[jamsheedm]

On Mar 27, 2:10 pm, Richard Heathfield <[e-mail].i nvalidwrote:

jamshe...@gmail .com said:

<snip>

printf("size of variable is %d\n",(char*)(& a+1)-(char*)(&a));
This will print the proper size of variable.

He didn't ask for the size of a variable, but for the size of a type.
Check the subject line: "sizeof dataTypes at run time".

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

Then there is no way to know the size of the type directly without
crating a variable of that type.
we can never use sizeof(double) or something like this.
Please let me know if anyone knows the solution for that.

[ramana]

On Mar 27, 3:20 pm, "jamshe...@gmai l.com" <jamshe...@gmai l.comwrote:

On Mar 27, 2:10 pm, Richard Heathfield <[e-mail].i nvalidwrote:

jamshe...@gmail .com said:

<snip>

printf("size of variable is %d\n",(char*)(& a+1)-(char*)(&a));
This will print the proper size of variable.

He didn't ask for the size of a variable, but for the size of a type.
Check the subject line: "sizeof dataTypes at run time".

Sorry for my misunderstandin g.

>

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

Then there is no way to know the size of the type directly without
crating a variable of that type.
we can never use sizeof(double) or something like this.
Please let me know if anyone knows the solution for that.

No its possible to know the size using the type itself. Check the
sample program below.

#include <stdio.h>

#define SIZE(x) ( (long)(((char*) ((x*)0 + 1)) - (char*)((x*)0)) )

int main()
{

printf(" sizes of char = %ld \t int = %ld \t float = %ld \t double =
%ld\n", SIZE(char), SIZE(int), SIZE(float), SIZE(double));

return 0;
}

I am new to posting to the groups. So i don't know the rules/practices
to follow. Please don't hesitate to tell me any that sort of stuff.

Thanks in advance.

--
Regards,
Ram

[Chris Dollin]

ramana wrote:

No its possible to know the size using the type itself. Check the
sample program below.

#include <stdio.h>

#define SIZE(x) ( (long)(((char*) ((x*)0 + 1)) - (char*)((x*)0)) )

int main()
{

printf(" sizes of char = %ld \t int = %ld \t float = %ld \t double =
%ld\n", SIZE(char), SIZE(int), SIZE(float), SIZE(double));

return 0;
}

The expression `(x*)0 + 1` (for whatever type `x`) is undefined.

So, although it may work on some (perhaps many; even, perhaps, all)
implementations , it's not guaranteed to work at all.

--
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"He's dead, Jim, but not as we know it." Unsaid /Trek/

Hewlett-Packard Limited registered no:
registered office: Cain Road, Bracknell, Berks RG12 1HN 690597 England

[Richard Heathfield]

ja*******@gmail .com said:

On Mar 27, 2:10 pm, Richard Heathfield <[e-mail].i nvalidwrote:

>>
He didn't ask for the size of a variable, but for the size of a type.
Check the subject line: "sizeof dataTypes at run time".

Then there is no way to know the size of the type directly without
crating a variable of that type.

Sure there is. It's called sizeof.

we can never use sizeof(double) or something like this.

Yes, we can.

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

[Ben Pfaff]

"ja*******@gmai l.com" <ja*******@gmai l.comwrites:

we can never use sizeof(double) or something like this.

It's always funny when people who don't know C try to instruct
others on how to use it.
--
Ben Pfaff
http://benpfaff.org