do screenshot from cmdline

windows-snapshot-tool/src/main.cpp

@@ -30,6 +30,17 @@ int WINAPI WinMain (HINSTANCE hThisInstance,
                     LPSTR lpszArgument,
                     int nCmdShow)
 {
+    LPWSTR *szArgList;
+    int argCount;
+    szArgList = CommandLineToArgvW(GetCommandLine(), &argCount);
+    if (szArgList != NULL && argCount >= 1) {
+        if (wcscmp(L"single", szArgList[1])==0) {
+            doScreenshot();
+            LocalFree(szArgList);
+            return 0;
+        }
+    }
+    LocalFree(szArgList);
 
     HWND existingApp = FindWindow(0, szClassName);
     if (existingApp)
@@ -256,7 +267,7 @@ void doScreenshot()
     WCHAR path[12];
     getRaspiStorage(path);
     if (wcslen(path) != 3) {
-        MessageBox(Hwnd, L"Couldn't find Raspberry USB-Storage\nSaving in current directory!", L"Failure", MB_OK);
+        if (Hwnd != NULL) MessageBox(Hwnd, L"Couldn't find Raspberry USB-Storage\nSaving in current directory!", L"Failure", MB_OK);
         CaptureImage(Hwnd, L"screenshot.png");
     } else {
         WCHAR filename[128];