Question

I followed a tutorial on some win32, creation and interaction, but I’m not sure how the code connects a “Write here” edit box to a message box.

#define IDC_MAIN_BUTTON 101         // Button identifier
#define IDC_MAIN_EDIT   102         // Edit box identifier
HWND hEdit;

LRESULT CALLBACK WinProc(HWND hWnd,UINT message,WPARAM wParam,LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInst,HINSTANCE hPrevInst,LPSTR lpCmdLine,int nShowCmd)
{
    WNDCLASSEX wClass;
    ZeroMemory(&wClass,sizeof(WNDCLASSEX));
    wClass.cbClsExtra=NULL;
    wClass.cbSize=sizeof(WNDCLASSEX);
    wClass.cbWndExtra=NULL;
    wClass.hbrBackground=(HBRUSH)COLOR_WINDOW;
    wClass.hCursor=LoadCursor(NULL,IDC_ARROW);
    wClass.hIcon=NULL;
    wClass.hIconSm=NULL;
    wClass.hInstance=hInst;
    wClass.lpfnWndProc=(WNDPROC)WinProc;
    wClass.lpszClassName="Window Class";
    wClass.lpszMenuName=NULL;
    wClass.style=CS_HREDRAW|CS_VREDRAW;

    if(!RegisterClassEx(&wClass))
    {
        int nResult=GetLastError();
        MessageBox(NULL,
            "Window class creation failed\r\n",
            "Window Class Failed",
            MB_ICONERROR);
    }

    HWND hWnd=CreateWindowEx(NULL,
            "Window Class",
            "Windows application",
            WS_OVERLAPPEDWINDOW,
            200,
            200,
            640,
            480,
            NULL,
            NULL,
            hInst,
            NULL);

    if(!hWnd)
    {
        int nResult=GetLastError();

        MessageBox(NULL,
            "Window creation failed\r\n",
            "Window Creation Failed",
            MB_ICONERROR);
    }

    ShowWindow(hWnd,nShowCmd);

    MSG msg;
    ZeroMemory(&msg,sizeof(MSG));

    while(GetMessage(&msg,NULL,0,0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

LRESULT CALLBACK WinProc(HWND hWnd,UINT msg,WPARAM wParam,LPARAM lParam)
{
    switch(msg)
    {
        case WM_CREATE:
        {

// How does this edit box, connect to the button?

            // Create an edit box
            hEdit=CreateWindowEx(WS_EX_CLIENTEDGE,
                "EDIT",
                "",
                WS_CHILD|WS_VISIBLE|
                ES_MULTILINE|ES_AUTOVSCROLL|ES_AUTOHSCROLL,
                50,
                100,
                200,
                100,8
                hWnd,
                (HMENU)IDC_MAIN_EDIT, GetModuleHandle(NULL), NULL);
            HGDIOBJ hfDefault=GetStockObject(DEFAULT_GUI_FONT);
            SendMessage(hEdit, WM_SETFONT, (WPARAM)hfDefault, MAKELPARAM(FALSE,0));
            SendMessage(hEdit, WM_SETTEXT, NULL, (LPARAM)"Insert text here...");

            // Create a push button
            HWND hWndButton=CreateWindowEx(NULL,
                "BUTTON",
                "OK",
                WS_TABSTOP|WS_VISIBLE|
                WS_CHILD|BS_DEFPUSHBUTTON,
                50,
                220,
                100,
                24,
                hWnd,
                (HMENU)IDC_MAIN_BUTTON, GetModuleHandle(NULL), NULL);
            SendMessage(hWndButton, WM_SETFONT, (WPARAM)hfDefault, MAKELPARAM(FALSE,0));
        }
        break;



        case WM_COMMAND:
            switch(LOWORD(wParam))
            {
                case IDC_MAIN_BUTTON:
                {
                    char buffer[256];
                    SendMessage(hEdit, WM_GETTEXT, sizeof(buffer)/sizeof(buffer[0]), reinterpret_cast<LPARAM>(buffer));
                    MessageBox(NULL, buffer, "Information", MB_ICONINFORMATION);
                }
                break;
            }
            break;

        case WM_DESTROY:
        {
            PostQuitMessage(0);
            return 0;
        }
        break;
    }

    return DefWindowProc(hWnd,msg,wParam,lParam);
}

I am really not sure how the text box sends its info to the message box.

Answer 1

The key is these three lines:

char buffer[256];
SendMessage(hEdit, WM_GETTEXT, sizeof(buffer)/sizeof(buffer[0]), reinterpret_cast<LPARAM>(buffer));
MessageBox(NULL, buffer, "Information", MB_ICONINFORMATION);

The WM_GETTEXT message does the following:

Copies the text that corresponds to a window into a buffer provided by the caller.

So the first call SendMessage will copy what’s in the hEdit window to the buffer you created the line before.

Then the next line writes the contents of buffer to the MessageBox