gethostbyaddr (original) (raw)

These functions shall retrieve information about hosts. This information is considered to be stored in a database that can be accessed sequentially or randomly. Implementation of this database is unspecified.

Note:

In many cases it is implemented by the Domain Name System, as documented in RFC 1034, RFC 1035, and RFC 1886.

Entries shall be returned in hostent structures.

The gethostbyaddr() function shall return an entry containing addresses of address family type for the host with address addr. The len argument contains the length of the address pointed to by addr. The_gethostbyaddr_() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

The gethostbyname() function shall return an entry containing addresses of address family AF_INET for the host with name_name_. The gethostbyname() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

The addr argument of gethostbyaddr() shall be an in_addr structure when type is AF_INET. It contains a binary format (that is, not null-terminated) address in network byte order. The gethostbyaddr() function is not guaranteed to return addresses of address families other than AF_INET, even when such addresses exist in the database.

If gethostbyaddr() returns successfully, then the h_addrtype field in the result shall be the same as the_type_ argument that was passed to the function, and the h_addr_list field shall list a single address that is a copy of the addr argument that was passed to the function.

The name argument of gethostbyname() shall be a node name; the behavior of gethostbyname() when passed a numeric address string is unspecified. For IPv4, a numeric address string shall be in the dotted-decimal notation described in inet_addr().

If name is not a numeric address string and is an alias for a valid host name, then gethostbyname() shall return information about the host name to which the alias refers, and name shall be included in the list of aliases returned.

Upon successful completion, these functions shall return a pointer to a hostent structure if the requested entry was found, and a null pointer if the end of the database was reached or the requested entry was not found.

Upon unsuccessful completion, gethostbyaddr() and gethostbyname() shall set h_errno to indicate the error.

The following sections are informative.

End of informative text.