"seekg identifier not found"

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
}