Set position of the put pointer.
  Sets the position of the put pointer. The put pointer determines the next location where to write in the buffer associated to the output stream.  

Parameters.

pos

The new position in the stream buffer. This parameter is an object of type streampos

off

Value of type streamoff indicating the offset in the stream's buffer. It is relative to dir parameter.

dir

Seeking direction. An object of type seekdir that may take any of the following values:

• ios_base::beg (seek from the beginning of the stream's buffer).
• ios_base::cur (seek from the current position in the stream's buffer).
• ios_base::end (seek from the end of the stream's buffer).

Return Value.
  The function returns *this

Example.

// position of put pointer
#include <fstream>
using namespace std;

int main () {
  long pos;

  ofstream outfile;
  outfile.open ("test.txt");

  outfile.write ("This is an apple",16);
  pos=outfile.tellp();
  outfile.seekp (pos-7);
  outfile.write (" sam",4);

  outfile.close();

  return 0;
}

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

typedef traits::pos_type pos_type; typedef traits::off_type off_type; basic_ostream& seekp ( pos_type pos ); basic_ostream& seekp ( off_type off, ios_base::seekdir dir );

See also.
  tellp, istream::seekg, istream::tellg
  ostream class