Thread: Size of structure in bytes

Consider this code:

Code:

#include <stdio.h>

typedef struct element
{
	char letter;
	struct element* next;
	
}element;
int main(void)
{
	printf("Sizeof structure element is: %d bytes!",sizeof(element));
}

If I compile this with Microsoft (Visual Studio .net) compiler and execute I get this result: Sizeof structure element is: 8 bytes!.

But if I compile this with Borlan Turbo C compiler I get this:
Sizeof structure element is: 3 bytes!.
I'm using Win XP. I know that Turbo C was used under DOS. In TC sizeof(void*) is 2 bytes which means that it behaves like it is run under 16-bit operating system. Win XP is 32 bit OS and in TC is probably 16-bit application and that's why I get these results. Can you confirm this conclusion?

What is interesting is somewhat unexpected result when using Visual Studio's compiler: 8 bytes and one could expect 5 bytes. Is that mean that structures can be only a multiple of 4. Why is that?

Thanks for help!

Do a board search for "padding" and "alignment"
Essentially, a compiler is free to add padding between members of a structure in order to ensure optimal alignment of data values within the structure.

Now you can trade compactness of structures against run-time performance if you want to by using say "#pragma pack(1)" (or some other compiler-specific notation).

It is aligning elements to the longword (32 bit) boundary because access is faster. On some 32-bit or 64-bit platforms misalignment of variables (not on a longword boundary) may result in a bus error. I believe Intel x86 systems are better off with a pointer on a longword boundary. I see the exact same thing on my PA RISC box.