ares_set_sortlist man page
ares_set_sortlist — Initialize an ares_channel sortlist configuration
#include <ares.h> int ares_set_sortlist(ares_channel channel, const char *sortstr)
The ares_set_sortlist(3) function initializes an address sortlist configuration for the channel data identified by channel, so that addresses returned by ares_gethostbyname(3) are sorted according to the sortlist. The provided sortstr string that holds a space separated list of IP-address-netmask pairs. The netmask is optional but follows the address after a slash if present. For example, "188.8.131.52/255.255.240.0 184.108.40.206".
This function replaces any potentially previously configured address sortlist with the ones given in the configuration string.
ares_set_sortlist(3) may return any of the following values:
The sortlist configuration was successfully initialized.
The process's available memory was exhausted.
The channel data identified by channel was invalid.
c-ares library initialization not yet performed.
ares_set_sortlist(3) was added in c-ares 1.11.0