sizeof and multi-dimensional arrays

[Jay A. Konigsberg]

In article <fred.663069060 at prisma> fred at prisma.cv.ruu.nl (Fred Appelman) writes:
>In <1991Jan5.050613.22303 at Neon.Stanford.EDU> dkeisen at Gang-of-Four.Stanford.EDU (Dave Eisen) writes:
>>Is the following a compiler bug or am I just confused?
>>
>>char x[2][3];
>>  sizeof (*x)          gives 6
>>  sizeof (x[0])        gives 3.
>>What's the scoop?
>
>You are just confused. 
>'x' is a two dimensional array of 2*3 elments of type char. Makes a total of
>6. 'x[0]' and 'x[1]' are arrays with a length of 3 elements. So both arrays
>have a size of 3.
>

Something is wrong here. I ran the program with the addition of sizeof(x)
and got the following:

sizeof(x[0])=3
sizeof(*x)=3
sizeof(x)=6

Also I bumped the array to "char x[5][6]" and got:

sizeof(x[0])=6
sizeof(*x)=6
sizeof(x)=30

This seems to be one of the finer differences between pointers and arrays.

sizeof(x)    makes sense as it is returning the total size declared for
	     the array.

sizeof(x[0]) makes sense as it returns the total size of that dimmension
	     of the array.

sizeof(*x)   DOES NOT make sense. The size of a pointer on this machine
	     is 4 bytes. (Note: adding "char *y; sizeof(y) does return 4).

-- 
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Jay @ SAC-UNIX, Sacramento, Ca.   UUCP=...pacbell!sactoh0!jak
If something is worth doing, it's worth doing correctly.