Question

I am trying to write header file. I can write simple headers like add(int x, y) return x+y; . But when I tried to get more complicated, visual studio gave error. I guess error is related to <fstream>. It always shows

“error C2065: ‘fstream’ : undeclared identifier “.

First line of my cpp file is void get_int(fstream& stream, int offset) (except #include<fstream>) and first definiton of .h file is

#ifndef GET_H
#define GET_H

int get_int(fstream& stream, int offset);

#endif

It goes like this. What is wrong with this code?

Answer 1

You must do this:

#ifndef GET_H
#define GET_H

#include <fstream>

int get_int(std::fstream& stream, int offset);

#endif

Notice the #include <fstream> and the added std:: prefix. The qualification is needed because all C++ Standard library… things… are defined in that namespace. You should not add a using namespace std; or using std::fstream; in a header, because that pollutes the global namespace and defeats the purpose of the existence of namespace std: people including your header don’t expect stuff to be pulled into the global namespace, which may conflict with naming used by others.