All functions return a exit code:
Idna_rc IDNA_SUCCESS = 0
Successful operation. This value is guaranteed to always be zero, the
remaining ones are only guaranteed to hold non-zero values, for
logical comparison purposes.
Idna_rc IDNA_STRINGPREP_ERROR
Error during string preparation.
Idna_rc IDNA_PUNYCODE_ERROR
Error during punycode operation.
Idna_rc IDNA_CONTAINS_LDH
For IDNA_USE_STD3_ASCII_RULES, indicate that the string contains LDH
ASCII characters.
Idna_rc IDNA_CONTAINS_MINUS
For IDNA_USE_STD3_ASCII_RULES, indicate that the string contains a
leading or trailing hyphen-minus (U+002D).
Idna_rc IDNA_INVALID_LENGTH
The final output string is not within the (inclusive) range 1 to 63
characters.
Idna_rc IDNA_NO_ACE_PREFIX
The string does not contain the ACE prefix (for ToUnicode).
Idna_rc IDNA_ROUNDTRIP_VERIFY_ERROR
The ToASCII operation on output string does not equal the input.
Idna_rc IDNA_CONTAINS_ACE_PREFIX
The input contains the ACE prefix (for ToASCII).
Idna_rc IDNA_ICONV_ERROR
Could not convert string in locale encoding.
Idna_rc IDNA_MALLOC_ERROR
Could not allocate buffer (this is typically a fatal error).