C++ header guard not working - c++

Question

I'm trying to get my includes working, but everything I try leads to errors. Even using #pragma once doesn't work. Do you know what I made wrong?
main.cpp
#include "utility/headers/Window.h"
#include "engine/headers/Player.h"
#include "engine/headers/Chunk.h"
ChunkManager.h
#ifndef CHUNK_MANAGER_H
#define CHUNK_MANAGER_H
#include "../../utility/headers/Vector3i.h"
#include "Chunk.h"
#include <map>
class ChunkManager{...}
#endif // CHUNK_MANAGER_H
Chunk.h
#pragma once
#ifndef CHUNK_H
#define CHUNK_H
#include <glm/glm.hpp>
#include "CubeCreator.h"
#include "ChunkManager.h"
#include "../../utility/headers/Random.h"
#include "../../utility/noise/headers/Noise.h"
class Chunk{...}
#endif // CHUNK_H
Error message is 'ChunkManager' has not been declared.
Thanks in advance!

Answer 1

Replace #include "ChunkManager.h" with class ChunkManager;.
That's called forward declaration and solves problems like class A needs to know about class B and class B needs to know about class A.
Depending on how you use ChunkManager in class Chunk. A forward declaration might not work.

Answer 2

Since non of the mentioned techniques worked in my case I defined a new header file containing global variables like chunkSize. Maybe it's just impossible to do what I've tried.
However for those who might find this question here's how my imports look now:
ChunkManager.h
#include "Chunk.h"
Chunk.h
// no includes
main.cpp
#include "ChunkManager.h"
And access to chunkSize isn't done anymore by calling ChunkManager::chunkSize but instead by calling Settings::chunkSize