From: Brian Candler <b.candler@...>
Date: 2009-12-03T02:59:17+09:00
Subject: Re: How to use rb_enc_str_new() to create a String with UTF-8 encoding?

I単aki Baz Castillo wrote:
> El Mi辿rcoles, 2 de Diciembre de 2009, Brian Candler escribi坦:
>> > How should I fill the third 'enc' argument?
>>     return rb_enc_from_index(idx);
>> }
> 
> Humm, it involves allocating memory for the rb_encoding object

Why? AFAICS, you can just pass a pointer to an existing encoding object. 
They are not mutated.

There are other examples, e.g. from io.c

#ifdef _WIN32
    if (utf16 == (rb_encoding *)-1) {
        utf16 = rb_enc_find("UTF-16LE");
        if (utf16 == rb_ascii8bit_encoding())
            utf16 = NULL;
    }
    if (utf16) {
        VALUE wfname = rb_str_encode(fname, rb_enc_from_encoding(utf16), 
0,
                                     Qnil);
        rb_enc_str_buf_cat(wfname, "", 1, utf16); /* workaround */
        data.fname = RSTRING_PTR(wfname);
        data.wchar = 1;
    }
    else {
        data.wchar = 0;
    }
#endif

It looks like rb_enc_from_encoding() takes a pointer to the rb_encoding 
object returned from rb_enc_find, and turns it into a VALUE
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