struct sockaddr_in member byte order for bind()

Question

I\'m learning socket programming and am confused by what I feel is inconsistent use of htons() and family of functions in my learning material. I\'m currently readi

Answer 1

Why is neither ntohs() nor htons() used on adr_inet.sin_family?

adr_inet.sin_family is initialized to the value of AF_INET. This is defined in bits/socket.h (which is called by netinet/in.h in your example) as:

#define PF_INET     2   /* IP protocol family.  */

and then,

#define AF_INET     PF_INET

So AF_INET is just a way for the program to identify the associated socket as a TCP/IP connection. It won't actually hold the value of an IPv4 address itself, so there's no need to perform an endian conversion on it.

Also, note that in newer iterations of C, netinet/in.h has a comment that states the following:

/* Functions to convert between host and network byte order.

   Please note that these functions normally take `unsigned long int' or
`unsigned short int' values as arguments and also return them.  But
this was a short-sighted decision since on different systems the types
may have different representations but the values are always the same.  */ 
extern uint32_t ntohl (uint32_t __netlong) __THROW __attribute__ ((__const__));
extern uint16_t ntohs (uint16_t __netshort)
        __THROW __attribute__ ((__const__));
extern uint32_t htonl (uint32_t __hostlong)
        __THROW __attribute__ ((__const__));
extern uint16_t htons (uint16_t __hostshort)
        __THROW __attribute__ ((__const__));

Whereas the website you're referencing cites the older use of unsigned long and unsigned short datatypes for the conversion functions. So there's a chance you may encounter issues running code from that site if you're using a newer version of C.