when does sizeof ( ) operator return zero !!

joeyBig · 10-01-2004, 02:07 AM

hi

When does the sizeof () operator return the value zero.

regards,
joe

rjlee · 10-01-2004, 03:58 AM

I guess you mean the C sizeof() operator (as opposed to, say, the PHP one).

The sizeof operator returns the size of its operand, in memory units (not necessarily bytes).
sizeof() a pointer will return the size of the thing the pointer points to; apparantly, it returns 1 for a pointer to a pointer (this makes sense, as you can ++ a pointer to make it point to the next element in a contiguous array)

I guess passing an empty struct or union (or C++ class) would return zero on some implementations but I wouldn't rely on it.

joeyBig · 10-01-2004, 05:54 AM

hi rjlee,
thanks for u'r information.
what u said is correct.
an empty structure or union is the answer.
empty class returns 1.

the doubt i got is,
in C, the size of an empty structure is 0 while in C++, it is 1.

why does this difference occurs.

regards,
joey

WhiteChedda · 10-01-2004, 06:43 AM

Quote:

Originally posted by joeyBig
hi

When does the sizeof () operator return the value zero.

regards,
joe

Make sure you tell the compiler to do strict ANSI C compiling. You SHOULD get a warning for C, as this is undefined behavior if I am remembering correctly and hence compiler dependent. Some compilers may have extentions to handle this in a non-standard fashion, and this might be what you are seeing.

As to C++ last time I used it, there was no standard, so I'm really not sure about that.