sendmessage callback error in visual studio 2012

sendmessage callback error in visual studio 2012

sendmessage callback error in visual studio 2012 I am recieving following
errors in this C function?
error C2220: warning treated as error - no 'object' file generated
warning C4100: 'wParam' : unreferenced formal parameter
warning C4100: 'hwnd' : unreferenced formal parameter
LRESULT CALLBACK WndProc (HWND hwnd,UINT message, WPARAM wParam,
LPARAM lParam)
{
switch (message) {
case WM_COPYDATA:
{
COPYDATASTRUCT* copy_data = (COPYDATASTRUCT*)(lParam);
const char* str = (const char* )(copy_data->lpData);
/* Also fixed the parameter list for "%.*s" */
printf("Message (%u): %.*s\n", copy_data->dwData,
(int)copy_data->cbData, str);
}
}
}