When working with IPv4 and IPv6 addresses, one often needs to convert their human-readable textual
representation into a binary numeric form and vice versa. The following two functions serve this
purpose:

The inet_pton function converts the textual representation into binary and inet_ntop the other way around. The binary form always uses the Network Byte Order.

The af argument specifies the address family (AF_INET or AF_INET6) and through the src and dst arguments the functions are given two pointers – src points to the buffer with the input value and dst to the buffer where the result is to be stored. Finally, the size argument of inet_ntop gives the size of the buffer allocated for the result. This buffer should be long enough to store a textual representation of any IPv4 or IPv6 address (depending on the chosen address family).

Function inet_pton returns 1 if the conversion was successful, 0 if the input value is considered wrong and -1 in the case of an unknown address family. In contrast, inet_ntop signals a failure by returning the NULL pointer, whereas if the conversion succeeds, the dst pointer is passed as the function return value, too.