Api function
#include <idn2.h>
int idn2_register_ul(const char * ulabel, const char * alabel, char ** insertname, int flags);
input zero-terminated locale encoded string, or NULL.
input zero-terminated ACE encoded string (xn--), or NULL.
newly allocated output variable with name to register in DNS.
optional idn2_flags to modify behaviour.
Perform IDNA2008 register string conversion on domain label ulabel and alabel, as described in section 4 of RFC 5891. Note that the input ulabel is assumed to be encoded in the locale's default coding system, and will be transcoded to UTF-8 and NFC normalized by this function.
It is recommended to supply both ulabel and alabel for better error checking, but supplying just one of them will work. Passing in only alabel is better than only ulabel. See RFC 5891 section 4 for more information.
On successful conversion IDN2_OK is returned, when the given ulabel and alabel does not match each other IDN2_UALABEL_MISMATCH is returned, when either of the input labels are too long IDN2_TOO_BIG_LABEL is returned, when alabel does does not appear to be a proper A-label IDN2_INVALID_ALABEL is returned, or another error code is returned.
The full documentation for libidn2 is maintained as a Texinfo manual. If the info and libidn2 programs are properly installed at your site, the command
info libidn2
should give you access to the complete manual.