Get/set the streambuf object associated with the stream.
  The first syntax returns the streambuf object associated with the stream.
  The second syntax associates the stream with streambuf object sb and returns the streambuf object previously associated with the stream.

Parameters.

sb

A pointer to the streambuf object to associate the stream with.

Return Value.
  A pointer to the streambuf object associated before the call.

Example.

// redirecting cout's output
#include <iostream>
#include <fstream>
using namespace std;

int main () {
  streambuf *psbuf;
  ofstream filestr;
  filestr.open ("test.txt");

  psbuf = filestr.rdbuf();
  cout.rdbuf(psbuf);

  cout << "This is written to the file";

  filestr.close();

  return 0;
}

Basic template member declaration ( basic_ios<charT,traits> ):

basic_streambuf<charT,traits> * rdbuf () const; basic_streambuf<charT,traits> * rdbuf ( basic_streambuf<charT,traits> sb );

See also.
  ios class