How do I make a tab control with children elements?

Question

I'm learning WINAPI, I read there's no children control in the sense a C#'s TabControl control does, so you have to create elements and show/hide by yourself. I read it may be done by drawing a dialog box inside tab page's area so I went to create a borderless dialog box being tab control's child, to make it have effect like C#'s. But I still couldn't make it. My dialog box is floating rather being tab control's child. I don't know to make it inside the tab page, I've tried setting the hWndParent to tab control's HWND and WS_EX_TOOLWINDOW | WS_EX_CONTROLPARENT flags in dwExStyle but still is floating over the tab control. Different approaches to solve this are welcome. I'm creating the tab control like this:

void AddTabControl(HWND hwnd)
{
    hTab = CreateWindowW(WC_TABCONTROLW, NULL,
            WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS | WS_TABSTOP,
            0, 30, 250, 250,
            hwnd,
            (HMENU) 9,
            NULL,
            NULL);
    InsertTabItem(hTab, 10, L"A");
    InsertTabItem(hTab, 11, L"B");
}

void InsertTabItem(HWND tabHwnd, UINT id, LPWSTR text)
{
    TCITEMW tci = {0};
    tci.mask = TCIF_TEXT;
    tci.pszText = text;
    tci.cchTextMax = lstrlenW(text);
    if(SendMessage(tabHwnd, TCM_INSERTITEMW, id, (LPARAM) &tci) == -1) {
        MessageBox(NULL, 
                    L"couldn't create the new tab page", 
                    L"tab errror",
                    MB_OK | MB_ICONERROR);
    }
}

And the dialog box like this:

void CreateDialogBox(HWND hwnd)
{
  CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_CONTROLPARENT, // WS_EX_TOOLWINDOW to hide window from ALT+TAB
        L"DialogClass", L"Dialog Box",
        WS_VISIBLE | WS_POPUP | WS_SYSMENU,
        100, 100, 400, 150,
        hTab, NULL, ghInstance,  NULL
  );
}

the result is:

the expected result (made from C#, just for example, ignore the color differences, I'll fix this later):

here's the full code:

#pragma comment(lib, "user32.lib")
#pragma comment(lib, "Comctl32.lib")

#define UNICODE

#include <windows.h>
#include <Commctrl.h>
#include <strsafe.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK DialogProc(HWND, UINT, WPARAM, LPARAM);

void CreateDialogBox(HWND);
void RegisterDialogClass(HWND);
void AddTabControl(HWND hwnd);
void InsertTabItem(HWND tabHwnd, UINT id, LPWSTR text);

HINSTANCE ghInstance;
HWND mainWindow;
HWND hTab;

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
    PWSTR pCmdLine, int nCmdShow) {

  MSG  msg = {0};
  HWND hwnd;

  WNDCLASSW wc = {0};

  wc.lpszClassName = L"Window";
  wc.hInstance     = hInstance;
  wc.hbrBackground = GetSysColorBrush(COLOR_3DFACE);
  wc.lpfnWndProc   = WndProc;
  
  RegisterClassW(&wc);
  hwnd = CreateWindowW(wc.lpszClassName, L"Window",
                WS_OVERLAPPEDWINDOW | WS_VISIBLE,
                100, 100, 500, 350, NULL, NULL, hInstance, NULL);  
  mainWindow = hwnd;
  ghInstance = hInstance;

  while( GetMessage(&msg, NULL, 0, 0)) {
    DispatchMessage(&msg);
  }
  
  return (int) msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{

  switch(msg)
  {
      case WM_CREATE:
          RegisterDialogClass(hwnd);
          AddTabControl(hwnd);
          CreateDialogBox(hwnd);
          break;

      case WM_COMMAND:
          CreateDialogBox(hwnd);
          break;

      case WM_DESTROY:
      {
          PostQuitMessage(0);
          return 0;
      }
  }
  return DefWindowProcW(hwnd, msg, wParam, lParam);
}

LRESULT CALLBACK DialogProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
  switch(msg) {
  
    case WM_CREATE:
        CreateWindowW(L"button", L"A",    
          WS_VISIBLE | WS_CHILD ,
          50, 50, 80, 25, hwnd, (HMENU) 1, NULL, NULL);  
        CreateWindowW(L"button", L"B", 
          WS_VISIBLE | WS_CHILD ,
          150, 50, 80, 25, hwnd, (HMENU) 2, NULL, NULL);
        CreateWindowW(L"button", L"C",
          WS_VISIBLE | WS_CHILD ,
          250, 50, 80, 25, hwnd, (HMENU) 3, NULL, NULL); 
    break;

    case WM_COMMAND:
        DestroyWindow(hwnd);
    break;

    case WM_CLOSE:
        DestroyWindow(hwnd);
        break;

  }
  
  return (DefWindowProcW(hwnd, msg, wParam, lParam));
}

void RegisterDialogClass(HWND hwnd) 
{
  WNDCLASSEXW wc = {0};
  wc.cbSize           = sizeof(WNDCLASSEXW);
  wc.lpfnWndProc      = (WNDPROC) DialogProc;
  wc.hInstance        = ghInstance;
  wc.hbrBackground    = GetSysColorBrush(COLOR_3DFACE);
  wc.lpszClassName    = L"DialogClass";
  RegisterClassExW(&wc);
}

void CreateDialogBox(HWND hwnd)
{
  CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_CONTROLPARENT, // WS_EX_TOOLWINDOW to hide window from ALT+TAB
        L"DialogClass", L"Dialog Box",
        WS_VISIBLE | WS_POPUP | WS_SYSMENU,
        100, 100, 400, 150,
        hTab, NULL, ghInstance,  NULL
  );
}

void AddTabControl(HWND hwnd)
{
    hTab = CreateWindowW(WC_TABCONTROLW, NULL,
            WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS | WS_TABSTOP,
            0, 30, 250, 250,
            hwnd,
            (HMENU) 9,
            NULL,
            NULL);
    InsertTabItem(hTab, 10, L"A");
    InsertTabItem(hTab, 11, L"B");
}

void InsertTabItem(HWND tabHwnd, UINT id, LPWSTR text)
{
    TCITEMW tci = {0};
    tci.mask = TCIF_TEXT;
    tci.pszText = text;
    tci.cchTextMax = lstrlenW(text);
    if(SendMessage(tabHwnd, TCM_INSERTITEMW, id, (LPARAM) &tci) == -1) {
        MessageBox(NULL, 
                    L"couldn't create the new tab page", 
                    L"tab errror",
                    MB_OK | MB_ICONERROR);
    }
}

Answer 1

When you created the dialog box control, you lacked the WS_CHILD style and added the WS_POPUP style, which caused the dialog box you generated to float.

You only need to modify it to the WS_CHILD style, and appropriately modify the size of the control to achieve your desired effect.

void CreateDialogBox(HWND hwnd)
{
    CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_CONTROLPARENT, // WS_EX_TOOLWINDOW to hide window from ALT+TAB
        L"DialogClass", L"Dialog Box",
        WS_VISIBLE  | WS_SYSMENU | WS_CHILD ,
        10, 30, 350, 150,
        hTab, NULL, ghInstance, NULL
    );
}

void AddTabControl(HWND hwnd)
{
    hTab = CreateWindowW(WC_TABCONTROLW, NULL,
        WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS | WS_TABSTOP,
        10, 30, 400, 250,
        hwnd,
        (HMENU)9,
        NULL,
        NULL);
    InsertTabItem(hTab, 10, L"A");
    InsertTabItem(hTab, 11, L"B");
}

It works like this: