filebuf in ifstream and ofstream

Question

How can i set a new char array to be the buffer of a fstream's filebuf, there is a function (setbuf) in the filebuf but it is protected. while searching on the web, some sites mention fstream::setbuf but it doesn't seem to exist anymore.

Thanks

Answer 1

The point of a protected member function is that it is meant to be overridden by your derived subclass. Here is a short section of the libstdc++ manual which discusses exactly that.

Here's an excerpt from <streambuf> which makes the same point in code:

  // [27.5.2.4.2] buffer management and positioning
  /**
   *  @brief  Manipulates the buffer.
   *
   *  Each derived class provides its own appropriate behavior.  See
   *  the next-to-last paragraph of 
   *  http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch25s02.html
   *  for more on this function.
   *
   *  @note  Base class version does nothing, returns @c this.
  */
  virtual basic_streambuf<char_type,_Traits>* 
  setbuf(char_type*, streamsize)
  { return this; }

Answer 2

streambuf is designed to be customized using the template method pattern, where the public methods are not virtual, and subclasses customize the behavior by implementing non-public virtual methods.

In the case at hand, the public method which calls setbuf is named pubsetbuf.

Note however that basic_filebuf's implementation of setbuf is rather loosely specified: The only guarantee is that setbuf(0, 0) makes the stream unbuffered. In other cases, the effect is implementation-defined.