C++ In a Nutshell

Stream Buffers

The I/O stream classes rely on stream buffers for the low-level input and output. Most programmers ignore the stream buffer and deal only with high-level streams. You might find yourself dealing with stream buffers from the client side—for example, using stream buffers to perform low-level I/O on entire streams at once—or you might find yourself on the other side, implementing a custom stream buffer. This section discusses both of these aspects.

You can copy a file in several ways. Example 9-3 shows how a C programmer might copy a stream once he has learned about templates.

Example 9-3. Copying streams one character at a time

template<typename charT, typename traits>
void copy(std::basic_ostream<charT, traits>& out,
          std::basic_istream<charT, traits>& in)
{
  charT c;
  while (in.get(c))
    out.put(c);
}

After measuring the performance of this solution, the intrepid programmer might decide that copying larger buffers is the right way to go. Example 9-4 shows the new approach. On my system, the new version runs roughly twice as fast as the original version. (Of course, performance measures depend highly on compiler, library, environment, and so on.)

Example 9-4. Copying streams with explicit buffers

template<typename charT, typename traits> void copy(std::basic_ostream<charT, traits>& out, std::basic_istream<charT, traits>& in) { const unsigned BUFFER_SIZE = 8192; std::auto_ptr<charT> buffer(new charT[BUFFER_SIZE]); while (in) { in.read(buffer.get( ), BUFFER_SIZE); out.write(buffer.get( ...