使程序只能运行一个唯一的实例

HANDLE g_hMutexOnly = NULL;
int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR     lpCmdLine,
int       nCmdShow)
{
g_hMutexOnly = CreateMutex( NULL, TRUE, _T("OnceOnlyMutex") );
if( g_hMutexOnly != NULL ) {
DWORD err = GetLastError();
if( err == ERROR_ALREADY_EXISTS ) {
//the program is already running
CloseHandle(g_hMutexOnly);
return -1;
}
}
else {
return 0;
}
MSG msg;
while( GetMessage( &msg, NULL, NULL, NULL ) )
{
TranslateMessage( &msg );
DispatchMessage( &msg );
}
CloseHandle(g_hMutexOnly);
return 0;
}

const TCHAR g_mainWndClassName[]=_T("MyWindowClass");
const TCHAR g_mainTitleName[]=_T("MyWindowTitle");
int APIENTRY WinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR     lpCmdLine,
int       nCmdShow)
{
HWND hwnd = FindWindowEx( NULL, NULL, g_mainWndClassName, g_mainTitleName );
if( hwnd )
return -1;
//register window class
//create window
CreateWindow( g_mainWndClassName, g_mainTitleName ... );
...
return 0;
}