WinAPI - C++ - How to completeley wipe/clear everything in window?

Question

I am using WinAPI in C++ for my application. I have painted some text and drawn a bitmap in the window by handling the WM_PAINT message. I have also put some button controls in the window via the CreateWindow function by handling the WM_CREATE message. I have spent hours researching this but i've had no luck - How can I completely clear the window and all of it's content (what i've put in it), so i'm left with an empty window with the same background title, etc, so I can put more buttons and stuff on it.

Here's My Code

#include <windows.h>
#include <string>
#include "mainheader.h"

const char g_szClassName[] = "myWindowClass";
HBITMAP bitmap;

//Window Procedure #Brain of the Window
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam){
    switch(msg){
        case WM_CREATE:{
            CreateWindow(TEXT("button"), TEXT("Play"),
                         WS_VISIBLE | WS_CHILD,
                         100, 227, 80, 25,
                             hwnd, (HMENU) 1, NULL, NULL);

            CreateWindow(TEXT("button"), TEXT("Stats"),
                         WS_VISIBLE | WS_CHILD,
                         200, 227, 80, 25,
                         hwnd, (HMENU) 2, NULL, NULL);

            CreateWindow(TEXT("button"), TEXT("Quit"),
                         WS_VISIBLE | WS_CHILD,
                         300, 227, 80, 25,
                         hwnd, (HMENU) 3, NULL, NULL);

            bitmap = (HBITMAP) LoadImage(NULL, TEXT("menuIcon.bmp"), IMAGE_BITMAP, 130, 130, LR_LOADFROMFILE);
            break;
        }

        case WM_COMMAND:{
            switch(LOWORD(wParam)){
                case 1:{
                    break;
                }

                case 2:{
                    break;
                }

                case 3:{
                    PostQuitMessage(0);
                }
            }

            break;
        }

        case WM_PAINT:{
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);
            HDC hMemDC = CreateCompatibleDC(hdc);

            ::SelectObject(hMemDC, bitmap);
            BitBlt(hdc, 170, 65, 200, 400, hMemDC, 0, 0, SRCCOPY);
            ::DeleteDC(hMemDC);

            SetBkColor(hdc, RGB(0, 0, 0));
            SetTextColor(hdc, RGB(0, 255, 0));

            std::string text = "Welcome to Tic Tac Toe v2.0!";
            std::string text2 = "Made By: Jaden Peterson (2015)";
            std::string text3 = "Please choose an option below:";

            TextOut(hdc, 150, 20, text.c_str(), text.length());
            TextOut(hdc, 141, 45, text2.c_str(), text2.length());
            TextOut(hdc, 145, 200, text3.c_str(), text3.length());
            EndPaint(hwnd, &ps);
            break;
        }

        case WM_CLOSE:{
            DestroyWindow(hwnd);
            break;
        }

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

        default:{
            return DefWindowProc(hwnd, msg, wParam, lParam);
        }
    }

    return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow){
    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;

    //Step 1: Registering the Window Class
    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = hInstance;
    wc.hIcon         = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_MYICON));
    wc.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = CreateSolidBrush(RGB(0, 0, 0));
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = g_szClassName;
    wc.hIconSm       = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_MYICON));

    if(!RegisterClassEx(&wc)){
        MessageBox(NULL, "Window Registration Failed!", "Error!", MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    //Creating the Window
    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        g_szClassName,
        "Tic Tac Toe v2.0",
        WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | WS_MINIMIZEBOX,
        CW_USEDEFAULT, CW_USEDEFAULT, 500, 300,
        NULL, NULL, hInstance, NULL);

    if(hwnd == NULL){
        MessageBox(NULL, "Window Creation Failed!", "Error!", MB_ICONEXCLAMATION | MB_OK);
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    //Message Loop #Heart of the Window
    while(GetMessage(&Msg, NULL, 0, 0) > 0){
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }

    return Msg.wParam;
}

Answer 1

Deleting all child windows is simple. Do a loop and enum all the child windows using EnumChildWindows . For each returned handle, call DestroyWindow.

First declare the callback function:

BOOL CALLBACK DestoryChildCallback(
  HWND   hwnd,
  LPARAM lParam
)
{
  if (hwnd != NULL) {
    DestroyWindow(hwnd)
  }

  return TRUE;
}

From your code:

EnumChildWindows(hwnd /* parent hwnd*/, DestoryChildCallback, NULL);