How can i emulate sizeof()

[Eugeny Myunster]

Hello all,
How can i emulate sizeof()
only for integers?

 

[Kenneth Brody]

Hello all,
How can i emulate sizeof()
only for integers?

I'd really love to know which instructors keep giving this assignment.

Why do you want to "emulate sizeof", when sizeof exists just for this
purpose?

How about:

#define MySizeof(x) sizeof(x)

Now you can "emulate sizeof" by using "MySizeof(int)", for example.

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:[email protected]>

 

[Keith Thompson]

I'd really love to know which instructors keep giving this assignment.

Why do you want to "emulate sizeof", when sizeof exists just for this
purpose?

How about:

#define MySizeof(x) sizeof(x)

Now you can "emulate sizeof" by using "MySizeof(int)", for example.

Except that the macro, unlike the sizeof operator, requires a
parenthesized argument; you can't write "MySizeof 42".

I'd use:

#define MySizeof sizeof

which is equally useful (i.e., not at all).

A serious answer to the original poster: Why do you want to do this?
There are ways to determine the size of an object without using the
sizeof operator, but there's no point in using them; the sizeof
operator exists for exactly this purpose.

Q: How do I pound in a nail? I don't want to use a hammer.
A: Use a hammer anyway; that's what it's for.

Having said that, it's not entirely pointless *as an exercise*.
Figuring out how to compute the size of something without using sizeof
does present an opportunity to demonstrate that you understand certain
aspects of the language. The resulting piece of code isn't going to
be useful in itself, but then neither is the classic "hello, world"
program; if I really want to print "hello, world" on stdout, I'll use
echo. (There's a GNU "hello" program, for example, but it exists
purely as a demo; it's not actually useful.) That's just the nature
of homework assignments.

Oh, and speaking of homework assignments: DO IT YOURSELF. What will
you learn if we just give you the answer? We're willing to offer
hints if you try to do it yourself, but if you want us to solve the
problem for you, please give us your instructor's e-mail address so we
can submit our solutions directly.

 

[user923005]

Hello all,
        How can i emulate sizeof()
        only for integers?

Of course, it is lunacy to use something else when you want a size,
since the sizeof operator is perfect for that task.

That having been said, you can make an array of 2 objects, and get an
unsigned char pointer to the first and second object and subtract the
pointer difference to find the size.

E.g.

#define StupidEvilTwistedSizeof(type,ans) { \
type a[2]; \
unsigned char *start = (unsigned char *)&a[0]; \
unsigned char *end = (unsigned char *)&a[1]; \
*ans=end-start;}

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

typedef struct thingy {
int a;
char b;
long c;
} thingy;

int main(void)
{
size_t size;
size_t *psize = &size;
StupidEvilTwistedSizeof(char, psize);
printf("I am ashamed to say that the size of char is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(short, psize);
printf("I am ashamed to say that the size of short is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(long, psize);
printf("I am ashamed to say that the size of long is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(long long, psize);
printf("I am ashamed to say that the size of long long is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(float, psize);
printf("I am ashamed to say that the size of float is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(double, psize);
printf("I am ashamed to say that the size of double is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(long double, psize);
printf("I am ashamed to say that the size of long double is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(thingy, psize);
printf("I am ashamed to say that the size of thingy is %u\n",
(unsigned) size);

return 0;
}
/*
Possible output:
I am ashamed to say that the size of char is 1
I am ashamed to say that the size of short is 2
I am ashamed to say that the size of long is 4
I am ashamed to say that the size of long long is 8
I am ashamed to say that the size of float is 4
I am ashamed to say that the size of double is 8
I am ashamed to say that the size of long double is 8
I am ashamed to say that the size of thingy is 12
*/

 

[user923005]

Hello all,
        How can i emulate sizeof()
        only for integers?

Of course, it is lunacy to use something else when you want a size,
since the sizeof operator is perfect for that task.

That having been said, you can make an array of 2 objects, and get an
unsigned char pointer to the first and second object and subtract the
pointer difference to find the size.

E.g.

#define StupidEvilTwistedSizeof(type,ans) { \
type a[2]; \
unsigned char *start = (unsigned char *)&a[0]; \
unsigned char *end = (unsigned char *)&a[1]; \
*ans=end-start;}

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

typedef struct thingy {
    int             a;
    char            b;
    long            c;

}   thingy;

int             main(void)
{
    size_t          size;
    size_t         *psize = &size;
    StupidEvilTwistedSizeof(char, psize);
    printf("I am ashamed to say that the size of char is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(short, psize);
    printf("I am ashamed to say that the size of short is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long, psize);
    printf("I am ashamed to say that the size of long is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long long, psize);
    printf("I am ashamed to say that the size of long long is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(float, psize);
    printf("I am ashamed to say that the size of float is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(double, psize);
    printf("I am ashamed to say that the size of double is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long double, psize);
    printf("I am ashamed to say that the size of long double is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(thingy, psize);
    printf("I am ashamed to say that the size of thingy is %u\n",
(unsigned) size);

    return 0;}

/*
Possible output:
I am ashamed to say that the size of char is 1
I am ashamed to say that the size of short is 2
I am ashamed to say that the size of long is 4
I am ashamed to say that the size of long long is 8
I am ashamed to say that the size of float is 4
I am ashamed to say that the size of double is 8
I am ashamed to say that the size of long double is 8
I am ashamed to say that the size of thingy is 12
*/

Updated version:

#define StupidEvilTwistedSizeof(type,ans) { \
type a[2]; \
unsigned char *start = (unsigned char *)&a[0]; \
unsigned char *end = (unsigned char *)&a[1]; \
*ans=end-start;}

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

typedef struct thingy {
int a;
char b;
long c;
} thingy;

typedef double (*PFI) ( double );

int main(void)
{
size_t size;
size_t *psize = &size;
StupidEvilTwistedSizeof(char, psize);
printf("I am ashamed to say that the size of char is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(short, psize);
printf("I am ashamed to say that the size of short is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(long, psize);
printf("I am ashamed to say that the size of long is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(long long, psize);
printf("I am ashamed to say that the size of long long is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(float, psize);
printf("I am ashamed to say that the size of float is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(double, psize);
printf("I am ashamed to say that the size of double is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(long double, psize);
printf("I am ashamed to say that the size of long double is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(thingy, psize);
printf("I am ashamed to say that the size of thingy is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(char *, psize);
printf("I am ashamed to say that the size of char * is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(int *, psize);
printf("I am ashamed to say that the size of int * is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(long *, psize);
printf("I am ashamed to say that the size of long * is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(void *, psize);
printf("I am ashamed to say that the size of void * is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(PFI, psize);
printf("I am ashamed to say that the size of PFI is %u\n",
(unsigned) size);
StupidEvilTwistedSizeof(void **, psize);
printf("I am ashamed to say that the size of void ** is %u\n",
(unsigned) size);

return 0;
}
/*
Possible output:
I am ashamed to say that the size of char is 1
I am ashamed to say that the size of short is 2
I am ashamed to say that the size of long is 4
I am ashamed to say that the size of long long is 8
I am ashamed to say that the size of float is 4
I am ashamed to say that the size of double is 8
I am ashamed to say that the size of long double is 8
I am ashamed to say that the size of thingy is 12
I am ashamed to say that the size of char * is 4
I am ashamed to say that the size of int * is 4
I am ashamed to say that the size of long * is 4
I am ashamed to say that the size of void * is 4
I am ashamed to say that the size of PFI is 4
I am ashamed to say that the size of void ** is 4
*/

 

[user923005]

Of course, it is lunacy to use something else when you want a size,
since the sizeof operator is perfect for that task.

That having been said, you can make an array of 2 objects, and get an
unsigned char pointer to the first and second object and subtract the
pointer difference to find the size.

E.g.

#define StupidEvilTwistedSizeof(type,ans) { \
type a[2]; \
unsigned char *start = (unsigned char *)&a[0]; \
unsigned char *end = (unsigned char *)&a[1]; \
*ans=end-start;}

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

typedef struct thingy {
    int             a;
    char            b;
    long            c;

}   thingy;

int             main(void)
{
    size_t          size;
    size_t         *psize = &size;
    StupidEvilTwistedSizeof(char, psize);
    printf("I am ashamed to say that the size of char is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(short, psize);
    printf("I am ashamed to say that the size of short is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long, psize);
    printf("I am ashamed to say that the size of long is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long long, psize);
    printf("I am ashamed to say that the size of long long is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(float, psize);
    printf("I am ashamed to say that the size of float is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(double, psize);
    printf("I am ashamed to say that the size of double is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long double, psize);
    printf("I am ashamed to say that the size of long double is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(thingy, psize);
    printf("I am ashamed to say that the size of thingy is %u\n",
(unsigned) size);

    return 0;}

/*
Possible output:
I am ashamed to say that the size of char is 1
I am ashamed to say that the size of short is 2
I am ashamed to say that the size of long is 4
I am ashamed to say that the size of long long is 8
I am ashamed to say that the size of float is 4
I am ashamed to say that the size of double is 8
I am ashamed to say that the size of long double is 8
I am ashamed to say that the size of thingy is 12
*/

Updated version:

#define StupidEvilTwistedSizeof(type,ans) { \
type a[2]; \
unsigned char *start = (unsigned char *)&a[0]; \
unsigned char *end = (unsigned char *)&a[1]; \
*ans=end-start;}

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

typedef struct thingy {
    int             a;
    char            b;
    long            c;

}               thingy;

typedef double (*PFI) ( double );

int             main(void)
{
    size_t          size;
    size_t         *psize = &size;
    StupidEvilTwistedSizeof(char, psize);
    printf("I am ashamed to say that the size of char is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(short, psize);
    printf("I am ashamed to say that the size of short is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long, psize);
    printf("I am ashamed to say that the size of long is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long long, psize);
    printf("I am ashamed to say that the size of long long is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(float, psize);
    printf("I am ashamed to say that the size of float is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(double, psize);
    printf("I am ashamed to say that the size of double is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long double, psize);
    printf("I am ashamed to say that the size of long double is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(thingy, psize);
    printf("I am ashamed to say that the size of thingy is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(char *, psize);
    printf("I am ashamed to say that the size of char * is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(int *, psize);
    printf("I am ashamed to say that the size of int * is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(long *, psize);
    printf("I am ashamed to say that the size of long * is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(void *, psize);
    printf("I am ashamed to say that the size of void * is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(PFI, psize);
    printf("I am ashamed to say that the size of PFI is %u\n",
(unsigned) size);
    StupidEvilTwistedSizeof(void **, psize);
    printf("I am ashamed to say that the size of void ** is %u\n",
(unsigned) size);

    return 0;}

/*
Possible output:
I am ashamed to say that the size of char is 1
I am ashamed to say that the size of short is 2
I am ashamed to say that the size of long is 4
I am ashamed to say that the size of long long is 8
I am ashamed to say that the size of float is 4
I am ashamed to say that the size of double is 8
I am ashamed to say that the size of long double is 8
I am ashamed to say that the size of thingy is 12
I am ashamed to say that the size of char * is 4
I am ashamed to say that the size of int * is 4
I am ashamed to say that the size of long * is 4
I am ashamed to say that the size of void * is 4
I am ashamed to say that the size of PFI is 4
I am ashamed to say that the size of void ** is 4
*/

The biggest problem with this method is that it works ONLY on types
and NOT on objects of a given type.
The sizeof operator works nicely on both.

 

[David Thompson]

Of course, it is lunacy to use something else when you want a size,
since the sizeof operator is perfect for that task.
Concur.

That having been said, you can make an array of 2 objects, and get an
unsigned char pointer to the first and second object and subtract the
pointer difference to find the size.

You don't even need an array of two: just a single object,
and use the address-one-past. You can't (safely, portably)
_dereference_ that address, but you can compute it.

And downthread

The biggest problem with this method is that it works ONLY on types
and NOT on objects of a given type.
The sizeof operator works nicely on both.

Concur again. Although you can do a sizeof_type which creates and
measures a dummy object, and a different sizeof_object which measures
an existing object. But you still can't match the operator for sizeof
a constant or other nonlvalue* expression such as the (hypothetical)
return of a function or function pointer. (* Ignoring the C99 glitch
that unintentionallly and crazily makes almost everything an lvalue.)

- formerly david.thompson1 || achar(64) || worldnet.att.net

 

[Kenny McCormack]

It's not lunacy, if a woman tells you she'll sleep with you if can write
a program that calculates the size of an object without using the
built-in sizeof operator. It becomes a very worthwhile endeavor.

That's the problem with a lot of the answers given here. They lack
context.

 

[Eligiusz Narutowicz]

It's not lunacy, if a woman tells you she'll sleep with you if can write
a program that calculates the size of an object without using the
built-in sizeof operator. It becomes a very worthwhile endeavor.

That's the problem with a lot of the answers given here. They lack
context.

I think the lack of context is more the problems of the question in this
case.

 

[Kenny McCormack]

It's not lunacy, if a woman tells you she'll sleep with you if can write
a program that calculates the size of an object without using the
built-in sizeof operator. It becomes a very worthwhile endeavor.

That's the problem with a lot of the answers given here. They lack
context.

I think the lack of context is more the problems of the question in this
case.
[/QUOTE]

I think (against the tide, I understand) that you should assume that a
poster has a reason for posting (as he does).

He should not have to justify that position beyond that which the fact
that he has posted has already done so.

 

[Richard Tobin]

I think (against the tide, I understand) that you should assume that a
poster has a reason for posting (as he does).

Yes, but for most of these sizeof() questions the context seems most
likely to be "I can't do the questions on my C test".

-- Richard

 

[Kenny McCormack]

Yes, but for most of these sizeof() questions the context seems most
likely to be "I can't do the questions on my C test".

-- Richard

"Passing the class" is probably an even more important - and more deserving
reason - than "I wanna get laid".

 

[El-Hassan Wanas]

I'd really love to know which instructors keep giving this assignment.

Why do you want to "emulate sizeof", when sizeof exists just for this
purpose?

How about:

    #define MySizeof(x) sizeof(x)

Now you can "emulate sizeof" by using "MySizeof(int)", for example.

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody        |www.hvcomputer.com| #include              |
| kenbrody/at\spamcop.net |www.fptech.com    |    <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:[email protected]>

I think it is a punishment for missing some homework or something. I
totally agree with the Macro approach. Ask your instructor, What is
the point of this assignment?, will I ever work on a project and try
to emulate this?

 

[Kenneth Brody]

"Passing the class" is probably an even more important - and more deserving
reason - than "I wanna get laid".

Quandry:

Professor says "get the size of an object without using sizeof".

SO says "don't".

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:[email protected]>