idn2_to_ascii_4i2 - Man Page

API function


#include <idn2.h>

int idn2_to_ascii_4i2(const uint32_t * input, size_t inlen, char ** output, int flags);


const uint32_t * input

zero terminated input Unicode (UCS-4) string.

size_t inlen

number of elements in  input .

char ** output

pointer to newly allocated zero-terminated output string.

int flags

optional idn2_flags to modify behaviour.


The ToASCII operation takes a sequence of Unicode code points that make up one domain label and transforms it into a sequence of code points in the ASCII range (0..7F). If ToASCII succeeds, the original sequence and the resulting sequence are equivalent labels.

It is important to note that the ToASCII operation can fail. ToASCII fails if any step of it fails. If any step of the ToASCII operation fails on any label in a domain name, that domain name MUST NOT be used as an internationalized domain name. The method for dealing with this failure is application-specific.

The inputs to ToASCII are a sequence of code points.

ToASCII never alters a sequence of code points that are all in the ASCII range to begin with (although it could fail). Applying the ToASCII operation multiple effect as applying it just once.

The default behavior of this function (when flags are zero) is to apply the IDNA2008 rules without the TR46 amendments. As the TR46 non-transitional processing is nowadays ubiquitous, when unsure, it is recommended to call this function with the IDN2_NONTRANSITIONAL and the IDN2_NFC_INPUT flags for compatibility with other software.

Return value: Returns IDN2_OK on success, or error code.



See Also

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. As an alternative you may obtain the manual from:


2.2.0 libidn2