#include <netinet/in.h>
The <netinet_in.h> header shall define the sa_family_t type as described in <sys/socket.h>.
The <netinet_in.h> header shall define the uint8_t and uint32_t types as described in <inttypes.h>. Inclusion of the <netinet/in.h> header may also make visible all symbols from <inttypes.h> and <sys/socket.h>.
The <netinet/in.h> header shall define the in_addr structure, which shall include at least the following member:
in_addr_t s_addr
The <netinet/in.h> header shall define the sockaddr_in structure, which shall include at least the following members:
sa_family_t sin_family AF_INET. in_port_t sin_port Port number. struct in_addr sin_addr IP address.
The sin_port and sin_addr members shall be in network byte order.
The sockaddr_in structure is used to store addresses for the Internet address family. Pointers to this type shall be cast by applications to struct sockaddr * for use with socket functions.
The <netinet/in.h> header shall define the in6_addr structure, which shall include at least the following member:
uint8_t s6_addr[16]
This array is used to contain a 128-bit IPv6 address, stored in network byte order.
The <netinet/in.h> header shall define the sockaddr_in6 structure, which shall include at least the following members:
sa_family_t sin6_family AF_INET6. in_port_t sin6_port Port number. uint32_t sin6_flowinfo IPv6 traffic class and flow information. struct in6_addr sin6_addr IPv6 address. uint32_t sin6_scope_id Set of interfaces for a scope.
The sin6_port and sin6_addr members shall be in network byte order.
Prior to calling a function in this standard which reads values from a sockaddr_in6 structure (for example, bind() or connect()), the application shall ensure that all members of the structure, including any additional non-standard members, if any, are initialized. If the sockaddr_in6 structure has a non-standard member, and that member has a value other than the value that would result from default initialization, the behavior of any function in this standard that reads values from the sockaddr_in6 structure is implementation-defined. All functions in this standard that return data in a sockaddr_in6 structure (for example, getaddrinfo() or accept()) shall initialize the structure in a way that meets the above requirements, and shall ensure that each non-standard member, if any, has a value that produces the same behavior as default initialization would in all functions in this standard which read values from a sockaddr_in6 structure.
The sin6_scope_id field is a 32-bit integer that identifies a set of interfaces as appropriate for the scope of the address carried in the sin6_addr field. For a link scope sin6_addr, the application shall ensure that sin6_scope_id is a link index. For a site scope sin6_addr, the application shall ensure that sin6_scope_id is a site index. The mapping of sin6_scope_id to an interface or set of interfaces is implementation-defined.
The <netinet/in.h> header shall declare the following external variable:
const struct in6_addr in6addr_any
This variable is initialized by the system to contain the wildcard IPv6 address. The <netinet/in.h> header also defines the IN6ADDR_ANY_INIT macro. This macro must be constant at compile time and can be used to initialize a variable of type struct in6_addr to the IPv6 wildcard address.
The <netinet/in.h> header shall declare the following external variable:
const struct in6_addr in6addr_loopback
This variable is initialized by the system to contain the loopback IPv6 address. The <netinet/in.h> header also defines the IN6ADDR_LOOPBACK_INIT macro. This macro must be constant at compile time and can be used to initialize a variable of type struct in6_addr to the IPv6 loopback address.
The <netinet/in.h> header shall define the ipv6_mreq structure, which shall include at least the following members:
struct in6_addr ipv6mr_multiaddr IPv6 multicast address. unsigned ipv6mr_interface Interface index.
The <netinet/in.h> header shall define the following symbolic constants for use as values of the level argument of getsockopt() and setsockopt():
The <netinet/in.h> header shall define the following symbolic constant for use as a local address in the structure passed to bind():
The <netinet/in.h> header shall define the following symbolic constant for use as a destination address in the structures passed to connect(), sendmsg(), and sendto():
The <netinet/in.h> header shall define the following symbolic constant, with the value specified, to help applications declare buffers of the proper size to store IPv4 addresses in string form:
The htonl(), htons(), ntohl(), and ntohs() functions shall be available as described in <arpa/inet.h>. Inclusion of the <netinet/in.h> header may also make visible all symbols from <arpa/inet.h>.
The <netinet/in.h> header shall define the following symbolic constant, with the value specified, to help applications declare buffers of the proper size to store IPv6 addresses in string form:
The <netinet/in.h> header shall define the following symbolic constants, with distinct integer values, for use in the option_name argument in the getsockopt() or setsockopt() functions at protocol level IPPROTO_IPV6:
The <netinet/in.h> header shall define the following macros that test for special IPv6 addresses. Each macro is of type int and takes a single argument of type const struct in6_addr *:
The following sections are informative.
Although it is common practice to initialize a sockaddr_in6 structure using:
struct sockaddr_in6 sa; memset(&sa, 0, sizeof sa);
this method is not portable according to this standard, because the structure can contain pointer or floating-point members that are not required to have an all-bits-zero representation after default initialization. Portable methods make use of default initialization; for example:
struct sockaddr_in6 sa = { 0 };
or:
static struct sockaddr_in6 sa_init; struct sockaddr_in6 sa = sa_init;
A future version of this standard may require that a pointer object with an all-bits-zero representation is a null pointer, and that sockaddr_in6 does not have any floating-point members if a floating-point object with an all-bits-zero representation does not have the value 0.0.
The System Interfaces volume of POSIX.1-2017, connect(), getsockopt(), htonl(), sendmsg(), sendto(), setsockopt()
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .