int main(int argc, char* argv[])
{
struct sockaddr_in addr1, addr2;
char* str_ptr;
char str_arr[20];
addr1.sin_addr.s_addr = htonl(0x10203040);
}
where s_addr is the variable declared in the in_addr structure.
What I'm curious about is why it's not an error when the in_addr structure has not even been declared?
(Excerpt part of the book code.)
The header file declared stdio.h, string.h, arpa/inet.h.
socket network c
If you check https://man7.org/linux/man-pages/man7/ip.7.html, sockaddr_in is defined as follows.
struct sockaddr_in {
sa_family_t sin_family; /* address family: AF_INET */
in_port_t sin_port; /* port in network byte order */
struct in_addr sin_addr; /* internet address */
};
/* /* Internet address */
struct in_addr {
uint32_t s_addr; /* address in network byte order */
};
In fact, if you look at Linux's /usr/include/netinet/in.h header, it is defined as follows:
typedef uint32_t in_addr_t;
struct in_addr
{
in_addr_t s_addr;
};
struct sockaddr_in
{
__SOCKADDR_COMMON (sin_);
in_port_t sin_port; /* Port number. */
struct in_addr sin_addr; /* Internet address. */
/* /* Pad to size of `struct sockaddr'. */
unsigned char sin_zero[sizeof (struct sockaddr)
- - __SOCKADDR_COMMON_SIZE
- - sizeof (in_port_t)
- - sizeof (struct in_addr)];
};
If you look at the above codes, the structure sockaddr_in has the member variable sin_addr.
This variable sin_addr has a s_addr member variable because it is a in_addr structure.
Therefore, addr1 has sin_addr, and this sin_addr has s_addr, so you can access addr1.sin_addr.s_addr in a series.
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