error LNK2005 already defined - Compiler error when building after running

Question

I'm trying to follow Riemer's DirectX with C++ tutorial.

I have made a few changes, for example here I have made my InitializeDevice() function in a separate file (tdirect.cpp / tdirect.h).

When I press F5 to compile and run, the program works perfectly. But when I make a change to a value (e.g. 0xff00ffff to 0xff0000ff - cyan to blue) without choosing the "Rebuild" option I get a stream of errors in my console which prevent me from compiling the program. This is pretty annoying as you can imagine. It's as if it's compiling tdirect.cpp twice.

Here's the source code of tdirect.cpp, tdirect.h, and the relevant part from main.cpp (tdirect.h is only included from main.cpp, and basicvertex.h is only included from tdirect.cpp)

tdirect.cpp:

#include "tdirect.h"
#include "basicvertex.h"

IDirect3D9 *pD3D;
D3DPRESENT_PARAMETERS D3DParams; 

LPDIRECT3DDEVICE9 InitializeDevice(HWND Wnd)
{
    pD3D = Direct3DCreate9(D3D_SDK_VERSION);
    if (pD3D == NULL)
    {
        MessageBox(Wnd, "DirectX is not installed.", "No DirectX!", MB_OK);
        return NULL;
    }

    ZeroMemory(&D3DParams, sizeof(D3DPRESENT_PARAMETERS));

    D3DParams.Windowed = TRUE;
    D3DParams.SwapEffect = D3DSWAPEFFECT_DISCARD;
    D3DParams.BackBufferFormat = D3DFMT_UNKNOWN;

    LPDIRECT3DDEVICE9 pDevice;
    if (FAILED(pD3D->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, Wnd, D3DCREATE_HARDWARE_VERTEXPROCESSING, &D3DParams, &pDevice)))
    {
        if (FAILED(pD3D->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_REF, Wnd, D3DCREATE_SOFTWARE_VERTEXPROCESSING, &D3DParams, &pDevice)))
        {
            MessageBox(Wnd, "Failed to create reference device.", "No software device!", MB_OK);
        }
        else {
            MessageBox(Wnd, "Falling back to software mode.", "No hardware device!", MB_OK);
        }
    }

    return pDevice;
}

LPDIRECT3DVERTEXBUFFER9 vBuffer;
void Init(LPDIRECT3DDEVICE9 pDevice)
{
    BASICVERTEX Vertices[3];
    Vertices[0].x = 150;
    Vertices[0].y = 100;
    Vertices[0].weight = 1;
    Vertices[0].colour = 0xffff0000;

    Vertices[1].x = 350;
    Vertices[1].y = 100;
    Vertices[1].weight = 1;
    Vertices[1].colour = 0xff00ff00;

    Vertices[2].x = 250;
    Vertices[2].y = 300;
    Vertices[2].weight = 1;
    Vertices[2].colour = 0xff00ffff;

    if (FAILED(pDevice->CreateVertexBuffer(sizeof(BASICVERTEX)*3, 0, D3DFVF_XYZRHW | D3DFVF_DIFFUSE, D3DPOOL_DEFAULT, &vBuffer, NULL)))
    {
        MessageBox(NULL, "Failed to create vertex buffer", "Fail", MB_OK);
    }
    else {
        void* pVertices;
        if (FAILED(vBuffer->Lock(0, sizeof(BASICVERTEX)*3, (void**)&pVertices, 0)))
        {
            MessageBox(NULL, "Failed to lock vertex buffer", "Fail", MB_OK);
        }
        else {
            memcpy(pVertices, Vertices, sizeof(BASICVERTEX)*3);
            vBuffer->Unlock();
        }
    }
}

void DrawScene(LPDIRECT3DDEVICE9 pDevice)
{
    pDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0,0,0), 1.0f, 0);
    pDevice->BeginScene();

    pDevice->SetStreamSource(0, vBuffer, 0, sizeof(BASICVERTEX));
    pDevice->SetFVF(D3DFVF_XYZRHW | D3DFVF_DIFFUSE);
    pDevice->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 1);

    pDevice->EndScene();
    pDevice->Present(NULL, NULL, NULL, NULL);
}

tdirect.h:

#pragma once
#include <Windows.h>

main.cpp include part:

#include <Windows.h>

#include "dxheader.h"
#include "tdirect.cpp"

Compiler Errors:

1>Debug\tdirect.obj : warning LNK4042: object specified more than once; extras ignored
1>main.obj : error LNK2005: "struct IDirect3DDevice9 * __cdecl InitializeDevice(struct HWND__ *)" (?InitializeDevice@@YAPAUIDirect3DDevice9@@PAUHWND__@@@Z) already defined in tdirect.obj
1>main.obj : error LNK2005: "void __cdecl Init(struct IDirect3DDevice9 *)" (?Init@@YAXPAUIDirect3DDevice9@@@Z) already defined in tdirect.obj
1>main.obj : error LNK2005: "void __cdecl DrawScene(struct IDirect3DDevice9 *)" (?DrawScene@@YAXPAUIDirect3DDevice9@@@Z) already defined in tdirect.obj
1>main.obj : error LNK2005: "struct IDirect3DVertexBuffer9 * vBuffer" (?vBuffer@@3PAUIDirect3DVertexBuffer9@@A) already defined in tdirect.obj
1>main.obj : error LNK2005: "struct _D3DPRESENT_PARAMETERS_ D3DParams" (?D3DParams@@3U_D3DPRESENT_PARAMETERS_@@A) already defined in tdirect.obj
1>main.obj : error LNK2005: "struct IDirect3D9 * pD3D" (?pD3D@@3PAUIDirect3D9@@A) already defined in tdirect.obj
1>C:\Users\me\Documents\Visual Studio 2010\Projects\DirectX\Debug\DXStuff.exe : fatal error LNK1169: one or more multiply defined symbols found

Thanks in advance :)

Answer 1

You're including an implementation file from your main.cpp, so it's adding the functions in again. You can't do this:

 #include "tdirect.cpp"

Instead you need to create a header file with the function prototypes so you can reference them...

Do you have these defined in your "tdirect.h" (this is what main.cpp should be including)?

LPDIRECT3DDEVICE9 InitializeDevice(HWND Wnd);

etc...