"Seekg id not found"

seekg is a method from the fstream class (declared in istream).

You haven't created any instances.

Let's take this as an example

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

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

      

        
        
        
      

    

source: http://www.cplusplus.com/reference/iostream/istream/seekg/

So you must

char* load_data(int begin_point,int num_characters)
{
    ifstream is;
    is("yourfile.txt") //file is now open for reading. 

    seekg(begin_point);
    char* return_val=new char[num_characters+1];
    mapdata.getline(return_val,num_characters);
    return return_val;
}

      

        
        
        
      

    

Please note what ParoXon commented in your question.

You should create a file other.cpp containing the load_data function. The other.h file must contain the load_data function declaration. In this file (other.h) you have to include all the files needed for the functions declared there to work. And don't forget to protect yourself from multiple inclusions!

File other.h

#ifndef __OTHER_H__
#define  __OTHER_H__

#include <iostream>
#include <fstream>

char* load_data(int,int);//no implementation
#endif

      

        
        
        
      

    

Other.cpp file

#include "other.h" //assumes other.h and other.cpp in same directory

char* load_data(int begin,int amount){
      //load_data implementation
}