sizeof

[pnreddy1976]

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

[Andrew Poelstra]

On 2006-06-18, Xicheng Jia <xi*****@gmail. com> wrote:

pn*********@gma il.com wrote:

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

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

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]

Andrew Poelstra <ap*******@loca lhost.localdoma in> writes:

On 2006-06-18, Xicheng Jia <xi*****@gmail. com> wrote:

pn*********@gma il.com wrote:

Hi,
How can we write a function, which functionality is similar to sizeof
function
any one send me source code
the problem is that the result of sizeof() is interpolated at compile
time. Can any function do it that way! :-)

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.

Why?
--
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.

[Xicheng Jia]

Andrew Poelstra wrote:

On 2006-06-18, Xicheng Jia <xi*****@gmail. com> wrote:

pn*********@gma il.com wrote:

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

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

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.

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]

pn*********@gma il.com writes:

How can we write a function, which functionality is similar to sizeof
function
Why would you want to do that?
any one send me source code

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) 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.

[Richard Heathfield]

ada said:

Andrew Poelstra <ap*******@loca lhost.localdoma in> writes:

<snip>

Not only that, but with C99
VLA's, sizeof /cannot/ be computer at compile time in some cases.

Why?

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)

[pete]

Madhav wrote:

Richard Heathfield wrote:

pn*********@gma il.com said:

Hi,
How can we write a function,
which functionality is similar to sizeof function

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

Can you tell us that reason, Richard?

The result of the sizeof operator must be a constant expression,
whenever the operand isn't a variable length array.

--
pete

[lovecreatesbeauty]

Richard Heathfield wrote:

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

Is following the inconsistent between the standard and implementations ?

#include <stdio.h>

int main(void)
{
int len = 10;
char a[len];

switch (sizeof a)
{
case 10:
printf("%s", "10 elements");
break;
default:
printf("<unknow >");
break;
}

fflush(stdout);

return 0;
}

$ gcc test.c
$ ./a.out
10 elements$
$

lovecreatesbeau ty

/*quoting begins*/
6.6 Constant expressions
2 A constant expression can be evaluated during translation rather than
runtime, <snip>

6.8.4.2 The switch statement
3 The expression of each case label shall be an integer constant
expression <snip>
/*quoting ends*/

[Dave Vandervies]

In article <df************ ********@bt.com >,
Richard Heathfield <in*****@invali d.invalid> wrote:

Madhav said:

Richard Heathfield wrote:

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

Can you tell us that reason, Richard?

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?

--------
template<class T>
std::size_t my_sizeof(const T&)
{
assert(HAS_FLAT _MEMORY_SPACE_A ND_UNCHECKED_PO INTER_ARITHMETI C);
T* x=0;
T* y=x+1;
return static_cast<std ::size_t>(
static_cast<cha r*>(y)-static_cast<cha r*>(x));
}
--------

If you'll excuse me while I go find a pointy stick to poke my sigmonster
with, I'll be right back...
dave

--
Dave Vandervies dj******@csclub .uwaterloo.ca
Suggesting to comp.lang.c that they use C++ compilers and inline assembly is
like suggesting to an American that you can get nice and warm by burning an
American flag. --Richard Heathfield in comp.lang.c

[lovecreatesbeauty]

Dave Vandervies wrote:

template<class T>
std::size_t my_sizeof(const T&)

C language has no template, namespace, :: and function overloading
things. Even you can't find any word same as "template", "namespace" or
"overload" in the standard document.

lovecreatesbeau ty

[Dave Vandervies]

In article <11************ *********@g10g2 000cwb.googlegr oups.com>,
lovecreatesbeau ty <lo************ ***@gmail.com> wrote:

Dave Vandervies wrote:

template<class T>
std::size_t my_sizeof(const T&)
C language has no template, namespace, :: and function overloading
things. Even you can't find any word same as "template", "namespace" or
"overload" in the standard document.

If you hadn't stopped reading there, and had been willing and able to
engage your brain while continuing to read, you would probably have
realized that I was aware of that.

(It also subtly fails to meet RH's spec, while providing enough
information to allow the OP to write (non-function) code to meet his
original spec without doing his homework for him. Which, really, is
all anybody could ask for in a homework thread.)
dave
(procrastinatin g doing homework of my own)

--
Dave Vandervies dj******@csclub .uwaterloo.caYup. Now, how does one fit this into a four-line .sig?

"People are stupid."
--Arvid Grotting and Mike Sphar in the Scary Devil Monastery