Question about netinet/ip.h

[Charles Swiger]

On Jun 1, 2006, at 12:57 AM, Emil Kondayan wrote:
> Can someone tell me why "ip_hl" and "ip_v" are of type "u_int" when  
> the
> structure is packed and they only fill a byte?

Well, that struct definition is relying on the compiler to squeeze  
the bitfields into the smallest space required.  Some platforms  
define ip_hl and ip_v as a char called ip_vhl instead:

/*
  * Structure of an internet header, naked of options.
  */
struct ip {
#ifdef _IP_VHL
         u_char  ip_vhl;                 /* version << 4 | header  
length >> 2 */
#else
[ ...bitfields vary based on BYTE_ORDER... ]

> And my second question:do these "#define ..." directives allocate  
> space in the
> structure?

No.  They define bitmasks to access each flag bit.

-- 
-Chuck