c++ - error LNK2019: unresolved external symbol error

I'm getting these error messages

2>main.obj : error LNK2019: unresolved external symbol "public: __thiscall CEngine::CEngine(void)" (??0CEngine@@QAE@XZ) referenced in function _WinMain@16

2>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall CEngine::SetWindowSize(int,int,char const *,int)" (?SetWindowSize@CEngine@@QAEXHHPBDH@Z) referenced in function _WinMain@16

2>main.obj : error LNK2019: unresolved external symbol "public: void __thiscall CEngine::Begin(void)" (?Begin@CEngine@@QAEXXZ) referenced in function _WinMain@16

2>main.obj : error LNK2019: unresolved external symbol "public: int __thiscall CEngine::GetDisplayWidth(void)" (?GetDisplayWidth@CEngine@@QAEHXZ) referenced in function _WinMain@16

2>main.obj : error LNK2019: unresolved external symbol "public: int __thiscall CEngine::GetDisplayHeight(void)" (?GetDisplayHeight@CEngine@@QAEHXZ) referenced in function _WinMain@16

2>C:\Users\ethan\Desktop\C++ Projects\delveenginetest\Debug\delveenginetest.exe : fatal error LNK1120: 5 unresolved externals

This is my solution:

Solution 'delveenginetest' (2 projects)

DelveEngine

Include

delve.h

Engine.h

SetupSDL.h

stdafx.h

Engine.cpp

Main.cpp

SetupSDL.cpp

This is the code for Engine.h

#pragma once
#include "SetupSDL.h"
class CEngine
{
public:
    CEngine(void);
    ~CEngine(void);
    void SetWindowSize(int winW, int winH, const char* GameName, int windowMode);
    void Begin(void);
    int GetDisplayWidth(void);
    int GetDisplayHeight(void);
private:
    int deskW;
    int deskH;
    bool playing;
    CSetupSDL* sdl_setup;
};

Code for Engine.cpp

#include "Include/stdafx.h"
#include "Include/Engine.h"
CEngine::CEngine(void)
{
    playing = true;
    deskW = GetSystemMetrics(SM_CXSCREEN);
    deskH = GetSystemMetrics(SM_CYSCREEN);
}
CEngine::~CEngine(void)
{
}
void CEngine::SetWindowSize(int winW, int winH, const char* GameName, int windowMode)
{
    // set up SDL for use
    sdl_setup = new CSetupSDL(winW, winH, GameName, windowMode);
}
void CEngine::Begin(void)
{
    while (playing && sdl_setup->GetMainEvent()->type != SDL_QUIT)
    {
        sdl_setup->Begin();
        sdl_setup->End();
    }
    playing = false;
}
int CEngine::GetDisplayWidth(void){ return deskW; }
int CEngine::GetDisplayHeight(void){ return deskH; }

The DelveEngine project builds successfully, whereas the delveenginetest project fails.

What's wrong? I've looked everywhere for a reason, can't find one that suits me.