std::stringstream o;

typedef std::ostreambuf_iterator<char> o_iter;

base64_t::decoder<o_iter> deciter(o_iter(o));

    std::istreambuf_iterator<char>(), deciter).eof().first=0;

x::base64::decoder is the comparable decoding output iterator. x::base64::decoder's template parameter is an output iterator class. x::base64::decoder expects to receive a base64-encoded sequence, which gets decoded and written to the output iterator class instance that's passed to x::base64::decoder's constructor.

Its eof() decodes any partially-received encoded sequence, then returns a std::pair. first is the final value of the output iterator originally given to the constructor. second is a bool which is true if the sequence was decoded with no errors, or false if the sequence contained any characters not a part of the base64 alphabet (excepting CR and LF).

size_t needed=base64_t::decoded_size(buffer.size());

decoded_size() estimates the size of a decoded base64 sequence, given the size of the encoded sequence. decoded_size() returns an upper estimate. The exact size cannot be known until the entire sequence gets decoded, because it depends on the presence of any padding characters or newlines. The value returned by decoded_size() is an upper estimate, for a buffer large enough to hold the largest possible decoded sequence from an encoded sequence of the given size.

auto res=base64_t::decode(buffer.begin(), buffer.end(), iter);


This is a convenience function that takes a pair of iterators, a beginning iterator, and an ending iterator for a base64-encoded sequence; and an output iterator. decode() constructs a x::base64::decoder using the output iterator passed as the third parameter, iterates over the input sequence, passing it to the instantiated x::base64::decoder, then invokes its eof() and returns the new output iterator and an indication whether the sequence was valid and did not contain characters other than those in the base64 alphabet.

This example base64-decodes the buffer container into the iter output iterator, then updating it with the new iterator value.