I'm trying to add a DirectX 11 renderer (not sure if that is even doable in a "simple" manner) to the Return To Castle Wolfenstein source code and I'm having some problems. I have a rendering class in a header that I included in the project, and whenever I include it in one of the RTCW files I get this error:

1>c:\program files (x86)\windows kits\8.1\include\um\directxmath.h(17): fatal error C1189: #error: DirectX Math requires C++

Now I am wondering what would be a way to use DirectX math functions/classes (and all DirectX classes actually) in a C project such as the RTCW code? Is it possible to change the entire project settings so it compiles as C++? I am using Visual Studio 2017.

This is my renderer class declaration in XD3D.h header:

#include <d3d11.h>
#include <DirectXMath.h>
#include "XGeomObject.h"
#include "XCamera.h"

using namespace DirectX; 

#define GPA(d3dModule, func) GetProcAddress(d3dModule, func)

class XD3DRenderer
{
protected:
    HMODULE                     m_XD3DModule;
    ID3D11Device*               m_pD3DDevice;
    ID3D11DeviceContext*        m_pDeviceContext;
    IDXGISwapChain*             m_pSwapChain;
    ID3D11RenderTargetView*     m_pRenderTargetView;
    ID3D11Texture2D*            m_pBackBuffer;
    ID3D11Texture2D*            m_pDepthStencilBuffer;
    ID3D11DepthStencilState*    m_pDepthStencilState;
    ID3D11DepthStencilState*    m_pDisabledDepthStencilState;
    ID3D11RasterizerState*      m_pRasterState;
    ID3D11DepthStencilView*     m_pDepthStencilView;

    HWND                        m_wnd;
    int                         m_screenWidth, m_screenHeight;
    bool                        m_fullScreen;
    D3DXMATRIX                  m_world, m_view, m_proj;
    bool                        m_lightMapsOn;

public:
    XD3DRenderer();
    XD3DRenderer(HWND wnd, int screenwidth, int screenheight,bool fullscreen);
    ~XD3DRenderer();

    ID3D11Device* GetD3DDevice() { return m_pD3DDevice; }
    ID3D11DeviceContext* GetDeviceContext() { return m_pDeviceContext; }

    bool LoadDriver();
    bool CreateD3DDevice(HWND wnd, int screenwidth, int screenheight, bool fullscreen );
    bool CreateRenderTargetView();
    bool CreateDepthBuffer();
    bool CreateDepthStencilView();
    bool CreateDisabledDepthStencilState();

    bool Setup();
    bool ClearScene(const D3DXCOLOR& col);
    bool Render(XGeomObject*, XCamera*);
    bool ShowScene();
    void TurnOnZBuffer();
    void TurnOffZBuffer();
};

And I include it in the C project in the RTCW win_glimp.c file like this:

#include <assert.h>
#include "../renderer/tr_local.h"
#include "../qcommon/qcommon.h"
#include "resource.h"
#include "glw_win.h"
#include "win_local.h"

#include "../renderer/XD3D.h"


extern void WG_CheckHardwareGamma( void );
extern void WG_RestoreGamma( void );

... rest of win_glimp.c file omitted.