structure sockaddr_in

[zio_mangrovia]

#include <sys/socket.h>
#include <netinet/in.h>

struct sockaddr_in {
  sa_family_t    sin_family; 
  in_port_t      sin_port;       /* network order */
  struct in_addr sin_addr;
};

struct in_addr {
  uint32_t s_addr;               /* network order */
};

Why It has been declared the structure in_addr ?
I could to declare the structure sockaddr_in as this one ?

struct sockaddr_in {
  sa_family_t    sin_family; 
  in_port_t      sin_port;       /* network order */
  uint32_t       s_addr; 
};

[salem_c]

1. _in isn't the only kind of address: See also https://man.archlinux.org/man/core/m...kaddr.3type.en

2. On your system for today, it happens to be a uint32. This won't be necessarily true for all systems across all of time.

3. The structure serves to document it's purpose. A bare uint32 could be anything.

4. If it became necessary to change what an 'in_addr' was, the structure means it's only changed in one place. Having just a bare uint32 is a massive search/replace with scope for lots of errors.

[VictorN]

...

struct in_addr {
  uint32_t s_addr;               /* network order */
};

Why It has been declared the structure in_addr ?
...

In addition to what salem_c already wrote I'd recommend to look at its definition in Microsoft winsock2.h file (in_addr structure (winsock2.h)):

struct in_addr {
  union {
    struct {
      u_char s_b1;
      u_char s_b2;
      u_char s_b3;
      u_char s_b4;
    } S_un_b;
    struct {
      u_short s_w1;
      u_short s_w2;
    } S_un_w;
    u_long S_addr;
  } S_un;
};