access violation at render function c++ directx9 - c++

Question

#include <Windows.h>
#include <d3dx9.h>
#include <sstream>
#include <string>
void initD3D(HWND hWnd);
void Render();
void cleanD3D();
LPDIRECT3D9 d3d ;
LPDIRECT3DDEVICE9 d3ddev;
LRESULT CALLBACK MainWindowProc(HWND hWnd,UINT uMsg,WPARAM wParam, LPARAM lParam)
{
switch(uMsg){
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hWnd,uMsg,wParam,lParam);
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,LPSTR lpCmdLine, int nCmdShow)
{
HWND mainWnd;
WNDCLASSEX wndClassData;
memset(&wndClassData, 0x00, sizeof(wndClassData));
wndClassData.cbSize = sizeof(wndClassData);
wndClassData.style = CS_CLASSDC;
wndClassData.lpfnWndProc = MainWindowProc;
wndClassData.hInstance = hInstance;
wndClassData.hCursor = LoadCursor(NULL, IDC_ARROW);
wndClassData.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
wndClassData.lpszClassName="ColourMatchingWindow";
RegisterClassEx(&wndClassData);
mainWnd = CreateWindowEx(NULL,
"wndClass",
"ColourMatching",
WS_OVERLAPPEDWINDOW,
100,100,
800,600,
GetDesktopWindow(),
NULL,
hInstance,
NULL);
ShowWindow(mainWnd, nCmdShow);
initD3D(mainWnd);
MSG msg;
for(;;){
while(PeekMessage(&msg, NULL,0,0,PM_REMOVE))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
if(msg.message==WM_QUIT)
break;
Render();
}
cleanD3D();
UnregisterClass("ColourMatchingWindow", hInstance);
return 0;
}
void initD3D(HWND hWnd){
d3d = Direct3DCreate9(D3D_SDK_VERSION);
D3DDISPLAYMODE displayMode;
d3d->GetAdapterDisplayMode(D3DADAPTER_DEFAULT, &displayMode);
D3DPRESENT_PARAMETERS d3dpp;
memset(&d3dpp, 0, sizeof(d3dpp));
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
d3dpp.hDeviceWindow = hWnd;
d3dpp.BackBufferFormat = displayMode.Format;
d3dpp.BackBufferCount = 1;
d3dpp.EnableAutoDepthStencil = TRUE;
d3dpp.AutoDepthStencilFormat = D3DFMT_D16;
d3d->CreateDevice(D3DADAPTER_DEFAULT,
D3DDEVTYPE_HAL,
hWnd,
D3DCREATE_SOFTWARE_VERTEXPROCESSING,
&d3dpp,
&d3ddev);
}
//---------------------problem starts here-------------------------
void Render(){
d3ddev->Clear(0, NULL, (D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER),
D3DCOLOR_ARGB(0, 0, 0, 0), 1.0f, 0);
d3ddev->BeginScene();
d3ddev->EndScene();
d3ddev->Present(NULL, NULL, NULL, NULL);
}
//------------------------problem ends-------------------------------
void cleanD3D(){
d3d->Release();
d3ddev->Release();
}
VS2010 gave me the error message about access violation at render() , and I tried to debug the code, realised that error might be caused by d3ddev wasn't assigned to a proper value, but im quite confused by why it is't assigned a proper value and whats the logic behind it? I thought d3ddev would be created once CreateDevice() was called, but it isn't for some reasons.