Set position of the get pointer.
  Sets the position of the get pointer. The get pointer determines the next location to be read in the buffer associated to the input stream.  

Parameters.

pos

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

off

Integer value of type streamoff representing the offset in the stream's buffer. It is relative to dir parameter.

dir

Seeking direction. It is an object of type ios_base::seekdir that can take any of the following constant values:

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

Return Value.
  The function returns *this

Example.

// read a file into memory
#include <iostream>
#include <fstream>
using namespace std;

int main () {
  int length;
  char * buffer;

  ifstream is;
  is.open ("test.txt", ios::binary );

  // get length of file:
  is.seekg (0, ios::end);
  length = is.tellg();
  is.seekg (0, ios::beg);

  // allocate memory:
  buffer = new char [length];

  // read data as a block:
  is.read (buffer,length);

  is.close();

  cout.write (buffer,length);

  return 0;
}

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

typedef traits::pos_type pos_type; typedef traits::off_type off_type; basic_istream<charT,traits> & seekg ( pos_type pos ); basic_istream<charT,traits> & seekg ( off_type off, ios_base::seekdir dir );

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