Can anyone provide an example of how to use windows ShutdownBlockReasonCreate - c++

Question

Can anyone provide a simple clear example of ShutdownBlockReasonCreate? I've been trying to figure it out through the MSDN pages but I'm not understanding it, and I'm getting really tired of having to turn off my computer every time I try and test it and it doesn't work. If someone is familiar and can provide a concise example that would be awesome!
This is what I have so far, but I do'
#include <Windows.h>
#include <iostream>
std::wstring s2ws(const std::string& s)
{
int len;
int slength = (int)s.length() + 1;
len = MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, 0, 0);
wchar_t* buf = new wchar_t[len];
MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, buf, len);
std::wstring r(buf);
delete[] buf;
return r;
}
int main(int argc, char* argv[])
{
if (ShutdownBlockReasonCreate(GetForegroundWindow(), s2ws("TEST").c_str()) != 0)
std::cout << "Success" << std::endl;
else
std::cout << "Failure" << std::endl;
while (1)
{
Sleep(1000);
std::cout << "Testing..." << std::endl;
}
}

Answer 1

This works for me in Windows 7. You could also do it in a console program if you liked, this was a simpler example to write. You should add error checking, I didn't to keep it short.
#include <SDKDDKVer.h>
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
HINSTANCE hInst;
HWND hWnd;
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
PAINTSTRUCT ps;
HDC hdc;
switch(message)
{
case WM_QUERYENDSESSION:
return FALSE;
break;
case WM_PAINT:
hdc = BeginPaint(hWnd, &ps);
EndPaint(hWnd, &ps);
break;
case WM_CREATE:
ShutdownBlockReasonCreate(hWnd, L"Don't do it!");
break;
case WM_DESTROY:
ShutdownBlockReasonDestroy(hWnd);
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEX wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wcex.lpszMenuName = NULL;
wcex.lpszClassName = L"TestClass";
wcex.hIconSm = NULL;
return RegisterClassEx(&wcex);
}
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
hInst = hInstance;
RECT sz = {0, 0, 512, 512};
AdjustWindowRect(&sz, WS_OVERLAPPEDWINDOW, TRUE);
hWnd = CreateWindow(L"TestClass", L"Test Window", WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT, sz.right - sz.left, sz.bottom - sz.top,
NULL, NULL, hInstance, NULL);
if(!hWnd)
{
return FALSE;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
return TRUE;
}
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
UNREFERENCED_PARAMETER(hPrevInstance);
UNREFERENCED_PARAMETER(lpCmdLine);
MyRegisterClass(hInstance);
if(!InitInstance(hInstance, nCmdShow))
{
return FALSE;
}
MSG msg;
while(GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int)msg.wParam;
}
A console version doesn't need to be drastically different, although you do need to create a window and run a message pump so I'm not sure what it buys you over a GUI app. Obviously if you want to do work in either version you'll most likely end up needing a separate thread for the window or for your work.
Here's the simplest example of a console program I came up with. You'll notice it's almost identical other than the ConsoleCtrlHandler to intercept the various ways of closing the console window and killing the GUI window instead. It's also expected to be a MBCS project since I didn't want to change it in my test console project.
#include <SDKDDKVer.h>
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
HINSTANCE hInst;
HWND hWnd;
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
PAINTSTRUCT ps;
HDC hdc;
switch(message)
{
case WM_QUERYENDSESSION:
return FALSE;
break;
case WM_PAINT:
hdc = BeginPaint(hWnd, &ps);
EndPaint(hWnd, &ps);
break;
case WM_CREATE:
ShutdownBlockReasonCreate(hWnd, L"Don't do it!");
break;
case WM_DESTROY:
ShutdownBlockReasonDestroy(hWnd);
PostQuitMessage(0);
break;
default:
return DefWindowProc(hWnd, message, wParam, lParam);
}
return 0;
}
ATOM MyRegisterClass(HINSTANCE hInstance)
{
WNDCLASSEX wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = hInstance;
wcex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wcex.lpszMenuName = NULL;
wcex.lpszClassName = "TestClass";
wcex.hIconSm = NULL;
return RegisterClassEx(&wcex);
}
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
hInst = hInstance;
RECT sz = {0, 0, 512, 512};
AdjustWindowRect(&sz, WS_OVERLAPPEDWINDOW, TRUE);
hWnd = CreateWindow("TestClass", "Test Window", WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT, sz.right - sz.left, sz.bottom - sz.top,
NULL, NULL, hInstance, NULL);
if(!hWnd)
{
return FALSE;
}
ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);
return TRUE;
}
BOOL WINAPI ConsoleCtrlHandler(DWORD dwCtrlType)
{
if(dwCtrlType == CTRL_C_EVENT ||
dwCtrlType == CTRL_BREAK_EVENT ||
dwCtrlType == CTRL_CLOSE_EVENT)
{
SendMessage(hWnd, WM_CLOSE, 0, 0);
return TRUE;
}
return FALSE;
}
int main()
{
SetConsoleCtrlHandler(ConsoleCtrlHandler, TRUE);
HINSTANCE hInstance = GetModuleHandle(NULL);
MyRegisterClass(hInstance);
if(!InitInstance(hInstance, SW_HIDE))
{
return FALSE;
}
MSG msg;
while(GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return (int)msg.wParam;
}

Answer 2

As you can probably guess by now, ShutdownBlockReasonCreate() does not actually block shutdown. All it does is tell Windows what message to say when it pops up this screen.
To block shutdown on Windows, you need to have a window. This means that you will need to write a GUI program that uses a standard message pump. WM_QUERYENDSESSION is a message that is sent to all windows when the system wants to shut down. You can handle the message to block the shutdown request. But to understand this, you will need to understand Windows GUI programming. (You might not need an actual GUI; a message-only window might work. I don't know for sure.)
Your first question on the matter was about blocking shutdown from a system service. I am not an expert on Windows services so I don't know the answer to that. Services should not have GUIs due to running on session 0, however. I don't know if they can have message-only windows either.