Question

u_char  ip_vhl;     /* version << 4 | header length >> 2 */

I can’t get it right , how is this done ?
can you give me examples on how to use this byte to store these 2 numbers
knowing that each one is 4 bit

Answer 1

ip_vhl = (version << 4) | (headerlen & 0xf);

Then the byte will look like this:

VVVVHHHH

To get back the original values:

version = ip_vhl >> 4;
headerlen = ip_vhl & 0xf;