Weird "classname" has not been declared - c++

Question

container.hpp
#ifndef CONTAINER_HPP
#define CONTAINER_HPP
#include <functional>
namespace lasd {
/* ************************************************************************** */
class Container {
private:
// ...
protected:
unsigned long size = 0;
public:
// Destructor
virtual ~Container() = default;
/* ************************************************************************ */
// Copy assignment
Container& operator=(const Container&) = delete; // Not usable.
// Move assignment
Container& operator=(Container&) = delete; // Not usable.
/* ************************************************************************ */
// Comparison operators
bool operator==(const Container&) const noexcept = delete; // Not usable.
bool operator!=(const Container&) const noexcept = delete; // Not usable.
/* ************************************************************************ */
// Specific member functions
virtual inline bool Empty() const noexcept;
virtual inline unsigned long Size() const noexcept;
virtual void Clear() = 0;
};
#include "container.cpp"
}
#endif
container.cpp
// Specific member functions (Container)
inline unsigned long Container::Size() const noexcept{
return size;
}
inline bool Container::Empty() const noexcept{
return size == 0;
}
Give this in output. The funniest part is that all this code is provided by my professor, and I only have coded the .cpp file. I've already tried to add #include "container.hpp" to my .cpp file.
||=== Build: Debug in Exercise1 (compiler: GNU GCC Compiler) ===|
||=== Build: Debug in Exercise1 (compiler: GNU GCC Compiler) ===|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp|4|error: 'Container' has not been declared|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp|4|error: non-member function 'long unsigned int Size()' cannot have cv-qualifier|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp||In function 'long unsigned int Size()':|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp|5|error: 'size' was not declared in this scope|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp|8|error: 'Container' has not been declared|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp|8|error: non-member function 'bool Empty()' cannot have cv-qualifier|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp||In function 'bool Empty()':|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp|9|error: 'size' was not declared in this scope|
C:\Users\Giulia\Desktop\Università\Laboratorio ASD\exercise1\container\container.cpp|38|error: expected initializer before '<' token|
||=== Build failed: 7 error(s), 0 warning(s) (0 minute(s), 1 second(s)) ===|
During professor video lectures, he has compiled the code and it worked so well. I really cannot understand why, by using Code::Blocks, it gives me this error (I've tried on the gpp-compiler on Atom editor too, with the exactly same result).
Thanks.

Answer 1

Most likely, in your project you are compiling container.cpp separately, as any reasonable project would do. However, your professor did something that would never pass any code review - he included a cpp file in a header file.
You need to change your project to not compile container.cpp separately (or better yet, get rid of that include and fix container.cpp to make it possible to compile it).

Answer 2

Note the namespace lasd in your header file. You should either explicitly namespace every function in your cpp file (lasd::Container::Size) or also wrap it in a namespace lasd { ... } block.