Hello *, I really enjoyed working with Iostreams, while testing some of my components. Using IOStreams with array_device seemed to be a very powerfull approach to test some of my stream based algorithms. But currently I face some issues which seem to be really weired to me. I produced some code snippet to better explain it. I used Boost.Test library to verify my assumptions. using namespace boost; namespace io=boost::iostreams; typedef unsinged char byte; typedef array arr_buffer; //boost::array typedef io::basic_array<byte> arr_dev; arr_buffer buffer_ = {{}}; arr_dev dev_(buffer_.begin(), buffer_.end()); io::stream ios_(dev_); arr_dev::pair_type range = dev_.input_sequence(); BOOST_MESSAGE("size: " << distance(range.first, range.second)); // output: size is 2 BOOST_CHECK_EQUAL(0u, ios_.tellg()); //stream is at position 0 as expected ios_.seekg(1); BOOST_CHECK_EQUAL(1u, ios_.tellg()); // stream is at position 1 as expected ios_.seekg(2); BOOST_MESSAGE("current pos: " << ios_.tellg()); // !!! stream is at position 2 ios_.seekg(3); BOOST_MESSAGE("current pos: " << ios_.tellg()); // stream is at position -1 BOOST_MESSAGE("eof: " << ios_.eof()); // !!! but eof is false If the defined stream is only 2 bytes long why is 2 a valid stream position? Why is eof always false? Do you think this behavior is buggy? I changed the same behavior to read bytes from stream and created an array of length 3, but passed the range of 2 bytes to the device ctor. This works as expected: arr_buffer buffer_ = {{'a', 'b', 'c'}}; arr_dev dev_(buffer_.begin(), buffer_.begin()+2); //range of 2 bytes is passed io::stream ios_(dev_); arr_dev::pair_type range = dev_.input_sequence(); BOOST_MESSAGE("size: " << distance(range.first, range.second)); byte bt; BOOST_MESSAGE("current pos: " << ios_.tellg()); // prints 0 BOOST_CHECK_EQUAL(0u, ios_.tellg()); ios_.read(&bt, 1); BOOST_MESSAGE("retrieved: " << bt); // prints 'a' BOOST_MESSAGE("current pos: " << ios_.tellg()); //prints 1 BOOST_CHECK_EQUAL(1u, ios_.tellg()); ios_.read(&bt, 1); BOOST_MESSAGE("retrieved: " << bt); // prints 'b' BOOST_MESSAGE("current pos: " << ios_.tellg()); // !!! prints 2, why not -1??? ios_.read(&bt, 1); BOOST_MESSAGE("retrieved: " << bt); // still prints 'b' => nothing retrieved BOOST_MESSAGE("current pos: " << ios_.tellg()); // !!! now it prints -1 BOOST_MESSAGE("eof: " << ios_.eof()); // !!! now eof is true Any ideas why it behaves as described? With Kind Regards, Ovanes