This streambuf base64-decodes all data read from the istream connected to it.
Note: For performance reasons, the characters are read directly from the given istream's underlying streambuf, so the state of the istream will not reflect that of its streambuf.
Direct Base Classes: UnbufferedStreamBuf
All Base Classes: UnbufferedStreamBuf
std::istream & istr,
int options = 0