Findwindow Does Not Find the a Window

FindWindow does not find the a window

 HWND Find = ::FindWindowEx(0, 0, "MozillaUIWindowClass", 0);

findwindow doesn't work c++

FindWindow works correctly. The possible causes for your problem are:

1. You have an encoding error. You should use the Unicode API:

   HWND hWnd = FindWindowW(NULL, L"Call of Duty®: Black Ops II - Multiplayer");
   

2. There is no top level window with that window text. Use a tool like Spy++ to check that.

You should also make sure that you read the documentation carefully. Specifically it states the following:

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

You should do as it says and call GetLastError in event of failure.

FindWindow() doesn't find my window [C++]

You are using ANSI strings with what appears to be the Unicode version of FindWindow.

Many Win32 functions are actually a pair of function and a macro. For example, FindWindow is defined approximately like this:

HWND WINAPI FindWindowA(LPCSTR lpClassName, LPCSTR lpWindowName);
HWND WINAPI FindWindowW(LPCWSTR lpClassName, LPCWSTR lpWindowName);

#if (UNICODE)
#  define FindWindow FindWindowW
#else
#  define FindWindow FindWindowA
#endif

Try explicitely calling FindWindowA or using wide strings like this:

HWND hwnd = FindWindow(L"iTunes", L"iTunes");

C++ FindWindow doesn't work

This issue may be that you're just casting a C-string to a T-string, which is probably a wide character string, so it's not going to work. Try this:

HWND hWnd = FindWindow(0,_T("Skype"));

This ensures the string constant is declared with the appropriate default character width that Windows API functions expect.

FindWindow( ... ) is not 'finding' created message window

I'm using a VS2013 console app. I've modified your code slightly to create a normal window and a message-only window and find both their handles by class name.

Output:

Normal window=00000000003A06FE Message-only window=00000000001F06CA
FindWindow=00000000003A06FE
FindWindowEx=00000000003A06FE
FindWindowEx(HWND_MESSAGE,...)=00000000001F06CA

Code:

typedef std::basic_string<TCHAR> tstring;

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

class MyWindow //: public CWnd
{
public:
    tstring className;
    HWND hwnd;
    HWND hwndMsgOnly;
    HWND find1;
    HWND find2;
    HWND find3;

    MyWindow::MyWindow(LPCTSTR pszClassName)
    {
        className = pszClassName;

        //auto wcn = ::AfxRegisterWndClass(NULL);
        //auto created = this->CreateEx(0, wcn, pszClassName, 0, 0, 0, 0, 0, HWND_MESSAGE, 0);

        // For a console app, `hInstance` is the instance of the program
        HINSTANCE hInstance = GetModuleHandle(0);

        WNDCLASSEX windowClass;
        windowClass.lpszClassName = pszClassName;
        windowClass.cbClsExtra = NULL;
        windowClass.cbWndExtra = NULL;
        windowClass.cbSize = sizeof(WNDCLASSEX);
        windowClass.hbrBackground = (HBRUSH)CreateSolidBrush(RGB(150, 0, 0));
        windowClass.hCursor = LoadCursor(NULL, IDC_ARROW);
        windowClass.hIcon = LoadIcon(NULL, MAKEINTRESOURCE(IDI_APPLICATION));
        windowClass.hIconSm = (HICON)LoadImage(NULL, MAKEINTRESOURCE(IDI_APPLICATION), IMAGE_ICON, 16, 16, NULL);
        windowClass.hInstance = hInstance;
        windowClass.lpfnWndProc = WindowProc;
        windowClass.lpszMenuName = NULL;
        windowClass.style = CS_VREDRAW | CS_HREDRAW;
        RegisterClassEx(&windowClass);
        hwnd = CreateWindowEx(NULL, pszClassName, _T("Basic Window"), WS_OVERLAPPEDWINDOW | WS_VISIBLE, 100, 100, 500, 500, NULL, NULL, hInstance, NULL);
        hwndMsgOnly = CreateWindowEx(NULL, pszClassName, _T("Dummy name"), 0, 0, 0, 0, 0, HWND_MESSAGE, NULL, NULL, NULL);
    }
};

void window_test(MyWindow & wnd)
{
    LPCTSTR pszClassName = wnd.className.c_str();
    wnd.find1 = FindWindow(pszClassName, nullptr); // = nullptr for OP version; okay for this version

    // or using FindWindowExW( ... )
    /**
        HWND hwndParent is a handle to the parent window whose child windows are to be searched.
        If hwndParent is NULL, the function uses the desktop window as the parent window.The function searches among windows that are child windows of the desktop.
        If hwndParent is HWND_MESSAGE, the function searches all message-only windows.
    **/
    HWND hWndParent = nullptr;
    wnd.find2 = FindWindowExW(hWndParent, nullptr, pszClassName, nullptr);// = nullptr for OP version; okay for this version
    hWndParent = HWND_MESSAGE;
    wnd.find3 = FindWindowExW(hWndParent, nullptr, pszClassName, nullptr);// = nullptr for OP version; finds the message-only window in this version
}

void main()
{
    MyWindow wnd(_T("test_window"));
    cout << "Normal window=" << wnd.hwnd << " Message-only window=" << wnd.hwndMsgOnly << endl;
    window_test(wnd);
    cout << "FindWindow=" << wnd.find1 << endl;
    cout << "FindWindowEx=" << wnd.find2 << endl;
    cout << "FindWindowEx(HWND_MESSAGE,...)=" << wnd.find3 << endl;
}

Why I cannot find window?

To summarize the comments there are two errors

1) (See @Tom Brunberg) is that the length is set incorrectly which is why you only get part (about half? of the string)

It should be

copyDataStruct.cbData := sizeof( Char )*(Length(stringToSend) + 1 );

2) The forms caption is being changed which invalidates the expression

FindWindow(PChar('TfrmReceiver'), PChar('frmReceiver'))

because the second parameter is the form's caption (in Delphi terminology)

Can't find window C++

Mode 1 : Use ::FindWindowEx()

Mode 2 : Get window handle from exe name(! Set exe name of Dead Island)

TCHAR* szExeName = _T("Dead Island"); //Dead Island.exe

HANDLE GetHandleOfDeadIsland()
{
    HANDLE hDeadIsland = INVALID_HANDLE_VALUE;
    HANDLE hSnap = INVALID_HANDLE_VALUE;
    PROCESSENTRY32 pe32;
    pe32.dwSize = sizeof(PROCESSENTRY32);

    hSnap = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);

    if (INVALID_HANDLE_VALUE != hSnap)
    {
        if (Process32First(hSnap, &pe32))
        {
            do 
            {
                //!!! Attention pe32.szExeFile always return exe file name. not window title.
                if (NULL != _tcsstr(pe32.szExeFile, szExeName))
                {
                    hDeadIsland = OpenProcess(PROCESS_ALL_ACCESS, TRUE, pe32.th32ProcessID);
                    break;
                }
            } while (Process32Next(hSnap, &pe32));
        }
    }

    return hDeadIsland;
}

int main()
{
    HANDLE hDeadIsland = GetHandleOfDeadIsland();
    if (INVALID_HANDLE_VALUE == hDeadIsland)
    {
        _tprintf(_T("Not Found\n"));
    }
    else
    {
        _tprintf(_T("Found\n"));
    }

    return GetLastError();
}

win32gui.FindWindow Not finding window

The line

shell.AppActivate("Tera Term VT")

works on the window title and therefore it works.

You should be able to to the same with

hwndMain = win32gui.FindWindow(None, "Tera Term VT")  

that is, swapping the arguments so that it also works based on the window title

If you want to work based on the window class name you could use a tool like Spy++ with its Finder Tool to target the Tera Term window and get its window class name from the properties

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