implementation of the 'sizeof' operator

[Aloo]

dear fellas,

this is anupam aka aloo and i have small problem

the problem ststes :--

But what if the the variable is gathered in a void pointer or the
element itself is given and not the data.

If you have any answers please mail it to my id
(e-mail address removed)

-thanks Aloo

 

[Richard Heathfield]

Aloo said:

the problem ststes :--


But what if the the variable is gathered in a void pointer

Then you're stuffed - but then, so is sizeof, so that's no hardship.

or the element itself is given and not the data.

I'm not sure exactly what you mean here. Could you please clarify?

 

[Aloo]

Aloo said:


Then you're stuffed - but then, so is sizeof, so that's no hardship.


I'm not sure exactly what you mean here. Could you please clarify?

well Richard,

first of all this problem was put up to me during an interview.

it stated :

let us say

that we need to implement the 'sizeof' operator without using sizeof
opearator of-course.

the data element is declared and the data inputed earlier. e.g.

....
....
int a;
scanf("%d",&a);
....
....


now at a later stage we need to know the size of the object 'a' with
the code above not visible to us. then what do we do ?

 

[DevarajA]

Aloo ha scritto:

well Richard,

first of all this problem was put up to me during an interview.

it stated :

let us say

that we need to implement the 'sizeof' operator without using sizeof
opearator of-course.

the data element is declared and the data inputed earlier. e.g.

...
...
int a;
scanf("%d",&a);
...
...


now at a later stage we need to know the size of the object 'a' with
the code above not visible to us. then what do we do ?

You could use two pointers, one to the variable and one to variable+1.
Then cast them to char* and subtract them.

type *pt1,*pt2;
int size;

pt1=pt2=&var;
size=((char*)++pt2-(char*)pt1);

 

[Richard Heathfield]

Aloo said:

that we need to implement the 'sizeof' operator without using sizeof
opearator of-course.

the data element is declared and the data inputed earlier. e.g.

...
...
int a;
scanf("%d",&a);
...
...


now at a later stage we need to know the size of the object 'a' with
the code above not visible to us. then what do we do ?

You can use a couple of char * to store (char *)&a and (char *)(&a + 1).

My last reply to you was written when I was very tired, and may contain much
that is apocryphal or even plain old brain-damaged, for which I apologise.

 

[Keith Thompson]

Aloo ha scritto: [...]

first of all this problem was put up to me during an interview.
it stated :
let us say
that we need to implement the 'sizeof' operator without using sizeof
opearator of-course.
the data element is declared and the data inputed earlier. e.g.
...
...
int a;
scanf("%d",&a);
...
...
now at a later stage we need to know the size of the object 'a' with
the code above not visible to us. then what do we do ?

You could use two pointers, one to the variable and one to
variable+1. Then cast them to char* and subtract them.

type *pt1,*pt2;
int size;

pt1=pt2=&var;
size=((char*)++pt2-(char*)pt1);

Gratuitous use of the ++ operator. There's also no need for either
pt1 or pt2.

size_t size = (char*)(&var+1) - (char*)(&var);