Updated: April 19, 2023 |
Get a network host entry, given an Internet address
#include <netdb.h> struct hostent * gethostbyaddr( const void * addr, socklen_t len, int type );
The gethostbyaddr() function searches for information associated with a host, which has the address pointed to by addr within the address family specified by type, opening a connection to the database if necessary.
This function returns a pointer to a structure of type hostent that describes an Internet host. This structure contains either the information obtained from a name server, or broken-out fields from a line in /etc/hosts.
You can use sethostent() to request the use of a connected TCP socket for queries. If the stayopen flag is nonzero, all queries to the name server will use TCP and the connection will be retained after each call to gethostbyaddr() or gethostbyname(). If the stayopen flag is zero, queries use UDP datagrams.
A pointer to a valid hostent structure, or NULL if an error occurs (h_errno is set).
See herror().
Use the gethostbyaddr() function to find a host:
struct sockaddr_in client; struct hostent* host; int sock, fd, len; … len = sizeof( client ); fd = accept( sock, (struct sockaddr*)&client, &len ); if( fd == -1 ) { perror( "accept" ); exit( 1 ); } host = gethostbyaddr( (const void*)&client.sin_addr, sizeof(struct in_addr), AF_INET ); printf( "Connection from %s: (%s)\n", host ? host->h_name : "<unknown>", inet_ntoa( client.sin_addr ) ); …
Standard Unix; removed from POSIX.1-2008
Safety: | |
---|---|
Cancellation point | Yes |
Interrupt handler | No |
Signal handler | No |
Thread | No |
This function uses static data storage; if you need the data for future use, copy it before any subsequent calls overwrite it. Currently, only the Internet address format is understood.