C and Sizeof question..

[Roger Oberholtzer]

On Wed, 2008-11-12 at 19:33 +0000, Steve Jardine wrote:
> Calling all C Gurus!!
> 
> Consider this C code:
> 
> #include <stdio.h>
> main() {
> 
> typedef struct {
> char           name[256];
> char           type[1]; 
> int             size;
> }resp;
> 
> char n[256];
> char t[1];
> 
> printf("sizeof resp is %d\n",sizeof(resp));
> printf("sizeof int is %d\n",sizeof(int));
> printf("Total: %d\n", sizeof(int)+sizeof(n)+sizeof(t));
> }
> 
> Can anyone explain why the sizeof the struct is 264 bytes, yet adding up all of its components yields 261 bytes?
> Call me confused...

Try this:

#include <stdio.h>

main() {

#	pragma pack(1)

	typedef struct {
		char	name[256];
		char	type[1]; 
		int	size;
}resp;

	char n[256];
	char t[1];

#	pragma pack(4)

	printf("sizeof resp is %d\n",sizeof(resp));
	printf("sizeof int is %d\n",sizeof(int));
	printf("Total: %d\n", sizeof(int)+sizeof(n)+sizeof(t));
}

We use this pragma when defining structures that will be sent to other
machine architectures. 

-- 
Roger Oberholtzer

OPQ Systems / Ramböll RST

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

Office: Int +46 8-615 60 20
Mobile: Int +46 70-815 1696

--

"On two occasions I have been asked (by members of Parliament!),
'Pray, Mr. Babbage, if you put into the machine wrong figures,
will the right answers come out?' I am not able rightly to apprehend
the kind of confusion of ideas that could provoke such a question.
  - Charles Babbage 1791-1871)
    English computer pioneer, philosopher

And remember:

It is RSofT and there is always something under construction. 
It is like talking about large city with all constructions finished. 
Not impossible, but very unlikely.