[Boost-users] Re: base64->wstring decoding

From: Robert Ramey (ramey_at_[hidden])
Date: 2005-03-11 00:10:02

This problem came about due to the fact I couldn't figure out how to
implement (in your code) decode(in.end()).   I really did try but concluded
that I couldn't do with out losing the ablity to buid up my string
translators by stepwise composition of inline code.  This latter was
important to me to guarentee optimal code generation so I wouldn't be
tempted to make a bunch of translators for every combination.

After much frustation I came to realized that it was easier to just avoid
using (decode(in.end())).  See test_iterators_base64

so use something like

So your case might be altered to interate not on the input characters but
rather on the output

> typedef
> transform_width<binary_from_base64<std::(w?)string::const_iterator>,32,6>
> decode;
>
> std::wostringstream out;

std::ostream_iterator<wchar_t,wchar_t> oit(out);
decode iit(s);

bits_size = in.size (32 / 6 ) // ?

while(bit_size-- > 0){
    *(oit++) = decode(*iit);

Other misc observations:

a) i notices you're using a 32 bit wchar_t - note that this is non-portable.
I would think about using std::vector<boost::int_least32>. or maybe instead
of using the "magic" number 32 you might want to try something like
(sizeof(wchar_t) * 8).

b) I'm not sure I remember where I handled the padding.  you should double
check that your if your original binary string isn't modulo 6 bits you might
find it filled with 0 after a round trip through base64.

Robert Ramey

Stefan Strasser wrote:
> Hi,
>
> I need to write a std::wstring which can contain binary data like \0
> to a xml attribute, so I'm converting it to base64 but I have problems
> decoding it:
> std::copy(decode(in.begin()),decode(in.end()),);
>
> is this a correct way to decode base64?
> it works, but only if (bits % 6 == 0).
> otherwise the program is abort()ed due to an exception.
>
> the string was encoded by
> base64_from_binary<transform_width<std::wstring::const_iterator,6,32>
> >
>
> Thanks,