"seekg identifier not found" - include

Question

I have a program called main:
#include<iostream>
#include<fstream>
using namespace std;
#include"other.h"
int main()
{
//do stuff
}
and then other.h:
char* load_data(int begin_point,int num_characters)
{
seekg(begin_point);
char* return_val=new char[num_characters+1];
mapdata.getline(return_val,num_characters);
return return_val;
}
and I get the error:
'seekg': identifier not found
why do I get this error and how do I fix it?

Answer 1

seekg is a method from the fstream (declared in istream) class.
You haven't instantiated any.
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 should
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;
}
Take into account what ParoXon commented in your question.
You should create a file other.cpp containing function's load_data implementation.
File other.h should contain function's load_data declaration. In that file (other.h) you should include all files neccesary for functions declared there to work. And dont forget to protect yourself against multiple includes !
File other.h
#ifndef __OTHER_H__
#define __OTHER_H__
#include <iostream>
#include <fstream>
char* load_data(int,int);//no implementation
#endif
File other.cpp
#include "other.h" //assumes other.h and other.cpp in same directory
char* load_data(int begin,int amount){
//load_data implementation
}