(Unicode C++) Punycode Encoding / Decoding

Punycode is an encoding standard for representing Unicode characters using only the 7bit us-ascii characters that are permitted in network host names. Punycode is used for internationalized domain names -- i.e. IDN or IDNA (Internationalizing Domain Names in Applications).

Punycode is defined in RFC 3492. Converting to/from punycode does not include the "xn--" prefix. The "xn--" prefix is to signify that punycode follows. For example, the string " café.com" is converted to "caf-dma.com" in punycode. The punycode domain name is "xn--caf-dma.com".

Converting an email address to punycode would be as follows. Suppose the email address is "coffee@café.com". The punycode representation is "coffee@xn--caf-dma.com". The RFC 3492 punycode representation of "café.com" is simply "caf-dma.com", but the punycode domain name is "xn--caf-dma.com".

The "xn--" is a constant. It is the same regardless of the domain. For example, the punycode URL representation of "mañana.com" is "xn--maana-pta.com".

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#include <CkStringBuilderW.h>

void ChilkatSample(void)
    {
    bool success;
    CkStringBuilderW sb;

    // Load the string "café" from a utf-8 text file.
    success = sb.LoadFile(L"qa_data/txt/cafe.txt",L"utf-8");

    sb.PunyEncode();
    wprintf(L"%s\n",sb.getAsString());

    sb.PunyDecode();
    wprintf(L"%s\n",sb.getAsString());

    // The output is:
    // 
    // caf-dma
    // café
    }