Issue with circular dependency even after separating definitions [duplicate] - c++

Question

This question already has answers here:
Resolve build errors due to circular dependency amongst classes
(12 answers)
Closed 7 years ago.
Please see my previous post here:
Undefined type error even with forward declaration
I moved the definitions to cpp files and I still face the issue. Any ideas why? My files look like this:
Header1.hpp
#ifndef HEADER1_HPP
#define HEADER1_HPP
namespace sample_ns
{
class sample_class{
public:
static int getNumber();
static void print();
};
}
#endif
Header2.hpp
#ifndef HEADER2_HPP
#define HEADER2_HPP
namespace sample_ns
{
class sample_class2{
public:
sample_class2();
int getNumber2();
};
}
#endif
Source1.cpp
#include "Header1.hpp"
#include "Header2.hpp"
#include "stdafx.h"
#include <iostream>
namespace sample_ns
{
int sample_class::getNumber()
{
sample_class2 obj;
return obj.getNumber2();
}
void sample_class::print()
{
std::cout << "Print utility function" << std::endl;
}
}
Source2.cpp
#include "Header2.hpp"
#include "Header1.hpp"
#include "stdafx.h"
#include <iostream>
namespace sample_ns
{
sample_class2::sample_class2()
{
sample_class::print();
}
int sample_class2::getNumber2()
{
sample_class::print();
return 5;
}
}
In my main I call it as:
std::cout << sample_ns::sample_class::getNumber() << std::endl;
I get 'sample_class2' : undeclared identifier. I tried adding class sample_class2; but that still gives me error
EDIT:
my main file:
#include "stdafx.h"
#include <iostream>
#include "Header1.hpp"
int _tmain(int argc, _TCHAR* argv[])
{
std::cout << "hello" << std::endl;
std::cout << sample_ns::sample_class::getNumber() << std::endl;
return 0;
}

Answer 1

The best practice for declaring classes and namespaces in header and cpp files is using structure likes below:
Header1.hpp
#ifndef HEADER1_HPP
#define HEADER1_HPP
#include "Header2.hpp"
#include <iostream>
namespace sample_ns
{
class sample_class{
public:
static int getNumber();
static void print();
};
}
#endif
Source1.cpp
#include "Header1.hpp"
namespace sample_ns
{
int sample_class::getNumber()
{
sample_class2 obj;
return obj.getNumber2();
}
void sample_class::print()
{
std::cout << "Print utility function" << std::endl;
}
}
So by including in header files and using ifndef you become sure that circular dependencies will not occure.