#include <sys/socket.h>
#include <netdb.h>
int getnameinfo(const struct sockaddr *restrict sa, socklen_t
salen,
char *restrict node, socklen_t nodelen,
char *restrict
service,
socklen_t servicelen, int flags);
The getnameinfo() function shall translate a socket address to a node name and service location, all of which are defined as in getaddrinfo() .
The sa argument points to a socket address structure to be translated.
If the socket address structure contains an IPv4-mapped IPv6 address or an IPv4-compatible IPv6 address, the implementation shall extract the embedded IPv4 address and lookup the node name for that IPv4 address.
If the node argument is non-NULL and the nodelen argument is non-zero, then the node argument points to a buffer able to contain up to nodelen characters that receives the node name as a null-terminated string. If the node argument is NULL or the nodelen argument is zero, the node name shall not be returned. If the node's name cannot be located, the numeric form of the address contained in the socket address structure pointed to by the sa argument is returned instead of its name.
If the service argument is non-NULL and the servicelen argument is non-zero, then the service argument points to a buffer able to contain up to servicelen bytes that receives the service name as a null-terminated string. If the service argument is NULL or the servicelen argument is zero, the service name shall not be returned. If the service's name cannot be located, the numeric form of the service address (for example, its port number) shall be returned instead of its name.
The flags argument is a flag that changes the default actions of the function. By default the fully-qualified domain name (FQDN) for the host shall be returned, but:
The getnameinfo() function shall be thread-safe.
A zero return value for getnameinfo() indicates successful completion; a non-zero return value indicates failure. The possible values for the failures are listed in the ERRORS section.
Upon successful completion, getnameinfo() shall return the node and service names, if requested, in the buffers provided. The returned names are always null-terminated strings.
The getnameinfo() function shall fail and return the corresponding value if:
The flags had an invalid value.
NI_NAMEREQD is set and the host's name cannot be located, or both nodename and servname were null.
An argument buffer overflowed. The buffer pointed to by the node argument or the service argument was too small.
The following sections are informative.
If the returned values are to be used as part of any further name resolution (for example, passed to getaddrinfo()), applications should provide buffers large enough to store any result possible on the system.
Given the IPv4-mapped IPv6 address "::ffff:1.2.3.4" , the implementation performs a lookup as if the socket address structure contains the IPv4 address "1.2.3.4" .
gai_strerror() , getaddrinfo() , getservbyname() , inet_ntop() , socket() , the Base Definitions volume of IEEE Std 1003.1-2001, <netdb.h>, <sys/socket.h>