Displaying text after left mouse button was clicked

Question

I want to display text only after I clicked with left mouse button into the client area of the window. I have this code, but it doesn't work. When I click left mouse button nothing happens:

void Text(HDC hdc)
{
    SetTextColor(hdc, RGB(255, 0, 0));
    SetBkColor(hdc, RGB(0, 0, 0));
    TCHAR display_msg[] = _T("Message in window");
    TextOut(hdc, RestartButtonWidth, 10, display_msg, _tcslen(display_msg));
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    HDC hdc;
    bool Clicked = false;

    switch (message)
    {
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);

        if (Clicked == true) 
        {
            Text(hdc);
        }          

        EndPaint(hWnd, &ps);
        break;

    case WM_LBUTTONDOWN:
        Clicked = true;
        break;

Why is the change of state of Clicked boolean not registered by WM_PAINT message?

Why should Clicked be true when you enter the CASE WM_PAINT block? — Grantly, Dec 01 '17 at 14:48
Please read a [good C++ book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) about scopes, and variable lifetime. — Algirdas Preidžius, Dec 01 '17 at 14:50
https://msdn.microsoft.com/en-us/library/windows/desktop/dd145002(v=vs.85).aspx — Hans Passant, Dec 01 '17 at 14:51
static bool Clicked = false; will solve your problem for now, but I agree with @AlgirdasPreidžius — Elvis Oric, Dec 01 '17 at 14:53

score 1 · Accepted Answer · answered Dec 01 '17 at 15:00

1

Every time your WndProc is called you create new variable Clicked. So, on WM_LBUTTONDOWN you set that local variable to true and that variable will be destroyed at the end of the scope. On the WM_PAINT event you are checking state of newly created Clicked variable and state of that variable is false.

static bool Clicked = false;

is quick solution for your problem.

answered Dec 01 '17 at 15:00

Elvis Oric

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Do have any idea how to do this in OOP? Because when I set class variable to static then I get error: unresolved external symbol – MPython Dec 01 '17 at 15:26
That's another problem. You probably just declared your static member, you also need to define that member. http://en.cppreference.com/w/cpp/language/static – Elvis Oric Dec 01 '17 at 15:31
bool ClassName::Clicked = false; // definition (does not use 'static') – Elvis Oric Dec 01 '17 at 15:36

Displaying text after left mouse button was clicked

1 Answers1