Editing Berkeley sockets (section)

===gethostbyname and gethostbyaddr===
The functions ''gethostbyname()'' and ''gethostbyaddr()'' are used to resolve host names and addresses in the [[domain name system]] or the local host's other resolver mechanisms (e.g., /etc/hosts lookup). They return a pointer to an object of type <var>struct hostent</var>, which describes an [[Internet Protocol]] host.  The functions use the following arguments:
* <var>name</var> specifies the name of the host.
* <var>addr</var> specifies a pointer to a <var>struct in_addr</var> containing the address of the host.
* <var>len</var> specifies the length, in bytes, of <var>addr</var>.
* <var>type</var> specifies the address family type (e.g., AF_INET) of the host address.

The functions return a NULL pointer in case of error, in which case the external integer {{mono|<var>h_errno</var>}} may be checked to see whether this is a temporary failure or an invalid or unknown host. Otherwise a valid <var>struct hostent *</var> is returned.

These functions are not strictly a component of the BSD socket API, but are often used in conjunction with the API functions for looking up a host. These functions are now considered legacy interfaces for querying the domain name system. New functions that are completely protocol-agnostic (supporting IPv6) have been defined. These new functions are [[getaddrinfo|getaddrinfo() and getnameinfo()]], and are based on a new ''[[addrinfo]]'' data structure.<ref>POSIX.1-2004</ref>

This pair of functions appeared at the same time as the BSD socket API proper in 4.2BSD (1983),<ref>{{man|3|gethostbyname|FreeBSD}}</ref> the same year DNS was first created. Early versions did not query DNS and only performed /etc/hosts lookup. The 4.3BSD (1984) version added DNS in a crude way. The current implementation using [[Name Service Switch]] derives Solaris and later NetBSD 1.4 (1999).<ref name="Conill">{{cite web |last1=Conill |first1=Ariadne |title=the tragedy of gethostbyname |url=https://ariadne.space/2022/03/27/the-tragedy-of-gethostbyname/ |website=ariadne.space |date=March 27, 2022}}</ref> Initially defined for [[NIS+]], NSS makes DNS only one of the many options for lookup by these functions and its use can be disabled even today.<ref>{{man|5|nsswitch.conf|FreeBSD}}</ref>