Wikipedia
The functions getaddrinfo and getnameinfo convert domain names, hostnames, and IP addresses between human-readable text representations and structured binary formats for the operating system's networking API. Both functions are contained in the POSIX standard application programming interface (API).
getaddrinfo and getnameinfo are inverse functions of each other. They are network protocol agnostic, and support both IPv4 and IPv6. It is the recommended interface for name resolution in building protocol independent applications and for transitioning legacy IPv4 code to the IPv6 Internet.
Internally, the functions perform resolutions using the Domain Name System (DNS) by calling other, lower level functions, such as gethostbyname .
On February 16 2016 a security bug was announced in the glibc implementation of getaddrinfo , using a buffer overflow technique, that may allow execution of arbitrary code by the attacker.