(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 <CkString.h>

void ChilkatSample(void)
    {
    CkString s;

    s.append("café");
    s.punyEncode();
    std::cout << s.getString() << "\r\n";

    s.prepend("xn--");
    s.append(".com");
    std::cout << s.getString() << "\r\n";

    s.replaceFirstOccurance("xn--","");
    s.replaceFirstOccurance(".com","");
    s.punyDecode();
    std::cout << s.getString() << "\r\n";

    //  The output is:
    // 
    //  	caf-dma
    //  	xn--caf-dma.com
    //  	café
    // 
    }