each_char

static VALUE
rb_str_each_char(VALUE str)
{
    long i, len, n;
    const char *ptr;
    rb_encoding *enc;

    RETURN_ENUMERATOR(str, 0, 0);
    str = rb_str_new4(str);
    ptr = RSTRING_PTR(str);
    len = RSTRING_LEN(str);
    enc = rb_enc_get(str);
    for (i = 0; i < len; i += n) {
        n = rb_enc_mbclen(ptr + i, ptr + len, enc);
        rb_yield(rb_str_subseq(str, i, n));
    }
    return str;
}