istream overloading when referencing another class [closed] - c++

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I have been stuck on what to do with this for loop inside an istream operator, i dont understand why it doesnt find >> operator.
Error C2679 binary '>>': no operator found which takes a right-hand operand of type 'Result' (or there is no acceptable conversion)
any help would be madly appreciated.
#include "pch.h"
#include <iostream>
#include <fstream>
#include "Unit.h"
#include "Registration.h"
istream & operator >>(istream & input, Unit & U);
ostream & operator <<(ostream & os, const Unit & U);
istream & operator >>(istream & input, Result & Re);
ostream & operator <<(ostream & os, const Result & Re);
istream & operator >>(istream & input, Date & D);
ostream & operator <<(ostream & os, const Date & D);
int main()
{
std::cout << "Hello World!\n";
ifstream infile("rinput.txt");
if (!infile)
{
return -1;
}
Registration R;
infile >> R;
ofstream ofile("routput.txt");
ofile << R
<< "Number of units = " << R.getCount() << '\n'
<< "Total credits = " << R.GetCredits() << '\n';
infile.close();
ofile.close();
}
#include "Registration.h"
using namespace std;
Registration::Registration()
{
}
istream & operator >>(istream & input, Registration & R)
{
long idTemp;
unsigned semesterTemp, countTemp;
Registration regTemp;
Result tempResult;
input >> idTemp >> semesterTemp >> countTemp;
regTemp.setStudentId(idTemp);
regTemp.setSemester(semesterTemp);
regTemp.setCount(countTemp);
for (unsigned i = 0; i < R.getCount(); i++)
{
//THIS LINE IS THE ERROR
input >> tempResult;
R.setResult(i, tempResult);
}
return input;
}
//result h file has the following
#ifndef RESULT_H
#define RESULT_H
#include "Date.h"
#include "Unit.h"
class Result
{
public:
Result();
float getMark() const;
void setMark(float mrk);
int GetCredits() const;
const Date & getDate() const;
void setDate(const Date &D);
const Unit & getUnit() const;
void setUnit(const Unit &U);
private:
float mark;
Date dateObject;
Unit unitObject;
};
#endif // !RESULT_H
this is the error:
Severity Code Description Project File Line Suppression State
Error C2679 binary '>>': no operator found which takes a right-hand operand of type 'Result' (or there is no acceptable conversion)
each class that is referenced inside result also has an overloading input stream function.

Answer 1

Here is a simple example
namespace Me {
class A
{
// bla
};
std::ostream& operator<<(std::ostream& os, A& const& obj)
{
// print in terms of public interface of A
// (else, deckare this a friend function inside A)
return os;
}
} // Me
int main()
{
std::cout << A(); // operator<<(ostream&, A const&) is the best match
}

Answer 2

C++ doesn't really have "source" or "header" files, it deals only with translation units.
A translation unit is, in short, a single source file with all included header files. Most importantly, a translation unit is its own independent unit, without any knowledge of other translation units.
That means declarations put in one translation unit (source file) will now be known by a different translation unit.
For a declaration to be known to all translation units that are linked into the final executable program, you should put them in a header file that is included everywhere needed.
Example:
Header file result.h:
#ifndef RESULT_H
#define RESULT_H
class Result
{
// ...
};
std::istream & operator >>(std::istream & input, Result & C);
std::ostream & operator <<(std::ostream & os, const Result & C);
#endif
"Main" source file main.cpp:
#include <iostream>
#include "result.h" // "Import" the `operator>>` declaration
int main()
{
Result result;
std::cin >> result;
}
"Result" class implementation source file result.cpp
#include <iostream>
#include "result.h"
// Result class implementation...
std::istream & operator >>(std::istream & input, Result & C)
{
// Read input...
return input;
}
When building the above example, you build the two source files separately as two separate translation units. The result of each translation unit is an object file. Then you link those two object files into the executable file.