先说明下，WS_CHILD样式的窗口一定要有父窗口，否则会创建失败，同时WS_CHILD的窗口也无法单独拖动，需要伴随父窗口移动而移动。

下面我们说下所有者窗口，在窗口创建时，如果没有指明WS_CHILD属性，同时hWndParent也指明了，则hWndParent为该窗口的所有者窗口。并且该窗口一定是显示在所有者窗口的上面，也就是说，所有者窗口不能覆盖被其拥有的窗口的区域。
另外如果通过::SetParent(hChildWnd, g_hWnd);则此新建的窗口除了所有者窗口外，还拥有父窗口，子窗口一定是在其父窗口的显示区域内显示(更准确的讲是客户区域)。并且SetParent并不会给窗口增加WS_CHILD属性，设置父窗口后，子窗口可以在父窗口的区域内拖动，并且，移动父窗口时，子窗口也跟着移动

如下图所示，点击大窗口左上角的创建子窗口后，会出现红色方框的被拥有者窗口，被拥有者窗口一定是覆盖在拥有者窗口之上，并且被拥有者窗口可以移出拥有者窗口的范围，并且大窗口(拥有者窗口)移动时，小窗口(被拥有者窗口)不会跟着移动。

如下图所示，可以看出此时小窗口无父窗口，但是有拥有者窗口。

这种情况下，对应的代码如下：

// TopmostTest.cpp : 定义应用程序的入口点。
//#include "framework.h"
#include "OwnerWndAndParentWnd.h"#define MAX_LOADSTRING 100#define IDB_ONE     3301  HWND g_hWnd = NULL;// 全局变量:
HINSTANCE hInst;                                // 当前实例
WCHAR szTitle[MAX_LOADSTRING];                  // 标题栏文本
WCHAR szWindowClass[MAX_LOADSTRING];            // 主窗口类名// 此代码模块中包含的函数的前向声明:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);int APIENTRY wWinMain(_In_ HINSTANCE hInstance,_In_opt_ HINSTANCE hPrevInstance,_In_ LPWSTR    lpCmdLine,_In_ int       nCmdShow)
{UNREFERENCED_PARAMETER(hPrevInstance);UNREFERENCED_PARAMETER(lpCmdLine);// TODO: 在此处放置代码。// 初始化全局字符串LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);LoadStringW(hInstance, IDC_OWNERWNDANDPARENTWND, szWindowClass, MAX_LOADSTRING);MyRegisterClass(hInstance);// 执行应用程序初始化:if (!InitInstance(hInstance, nCmdShow)){return FALSE;}HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_OWNERWNDANDPARENTWND));MSG msg;// 主消息循环:while (GetMessage(&msg, nullptr, 0, 0)){if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)){TranslateMessage(&msg);DispatchMessage(&msg);}}return (int)msg.wParam;
}//
//  函数: MyRegisterClass()
//
//  目标: 注册窗口类。
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{WNDCLASSEXW wcex;wcex.cbSize = sizeof(WNDCLASSEX);wcex.style = CS_HREDRAW | CS_VREDRAW;wcex.lpfnWndProc = WndProc;wcex.cbClsExtra = 0;wcex.cbWndExtra = 0;wcex.hInstance = hInstance;wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_OWNERWNDANDPARENTWND));wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);wcex.lpszMenuName = MAKEINTRESOURCEW(IDC_OWNERWNDANDPARENTWND);wcex.lpszClassName = szWindowClass;wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));return RegisterClassExW(&wcex);
}//
//   函数: InitInstance(HINSTANCE, int)
//
//   目标: 保存实例句柄并创建主窗口
//
//   注释:
//
//        在此函数中，我们在全局变量中保存实例句柄并
//        创建和显示主程序窗口。
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{hInst = hInstance; // 将实例句柄存储在全局变量中HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);if (!hWnd){return FALSE;}ShowWindow(hWnd, nCmdShow);g_hWnd = hWnd;//::SetWindowPos(hWnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_SHOWWINDOW);UpdateWindow(hWnd);return TRUE;
}//
//  函数: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  目标: 处理主窗口的消息。
//
//  WM_COMMAND  - 处理应用程序菜单
//  WM_PAINT    - 绘制主窗口
//  WM_DESTROY  - 发送退出消息并返回
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{switch (message){case WM_COMMAND:{int wmId = LOWORD(wParam);// 分析菜单选择:switch (wmId){case IDM_ABOUT:DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);break;case IDM_EXIT:DestroyWindow(hWnd);break;case IDB_ONE:{///此处创建一个非topmost的子窗口HWND hChildWnd = ::CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_DLGMODALFRAME, L"OWNERWNDANDPARENTWND", L"MyClildTitle", WS_VISIBLE | WS_OVERLAPPEDWINDOW, 600, 600, 200, 200, g_hWnd, NULL, hInst, nullptr);//HWND hChildWnd = ::CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_DLGMODALFRAME, L"TOPMOSTTEST", L"MyClildTitle", WS_VISIBLE | WS_OVERLAPPEDWINDOW, 800, 800, 200, 200, NULL, NULL, hInst, nullptr);DWORD err = ::GetLastError();//::SetParent(hChildWnd, g_hWnd);break;}default:return DefWindowProc(hWnd, message, wParam, lParam);}}break;case WM_PAINT:{PAINTSTRUCT ps;HDC hdc = BeginPaint(hWnd, &ps);// TODO: 在此处添加使用 hdc 的任何绘图代码...EndPaint(hWnd, &ps);}break;case WM_DESTROY:PostQuitMessage(0);break;case WM_CREATE:{//CreateWindowW(L"Button", L"创建非topmost子窗口", WS_VISIBLE | WS_CHILD | BS_PUSHBUTTON, 35, 10, 200, 60, hWnd, (HMENU)IDB_ONE, hInst, NULL);HWND hChild = CreateWindowW(L"Button", L"创建子窗口", WS_VISIBLE | WS_CHILD | BS_PUSHBUTTON, 35, 10, 200, 60, hWnd, (HMENU)IDB_ONE, hInst, NULL);DWORD err = ::GetLastError();int i = 0;i++;}break;default:return DefWindowProc(hWnd, message, wParam, lParam);}return 0;
}// “关于”框的消息处理程序。
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{UNREFERENCED_PARAMETER(lParam);switch (message){case WM_INITDIALOG:return (INT_PTR)TRUE;case WM_COMMAND:if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL){EndDialog(hDlg, LOWORD(wParam));return (INT_PTR)TRUE;}break;}return (INT_PTR)FALSE;
}

然后我们给此小窗口设置父窗口(通过SetParent)，设置后会发现，小窗口只能在大窗口的内部显示，并且，大窗口移动时，小窗口会跟着移动。

对应的代码如下：

// TopmostTest.cpp : 定义应用程序的入口点。
//#include "framework.h"
#include "OwnerWndAndParentWnd.h"#define MAX_LOADSTRING 100#define IDB_ONE     3301  HWND g_hWnd = NULL;// 全局变量:
HINSTANCE hInst;                                // 当前实例
WCHAR szTitle[MAX_LOADSTRING];                  // 标题栏文本
WCHAR szWindowClass[MAX_LOADSTRING];            // 主窗口类名// 此代码模块中包含的函数的前向声明:
ATOM                MyRegisterClass(HINSTANCE hInstance);
BOOL                InitInstance(HINSTANCE, int);
LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);int APIENTRY wWinMain(_In_ HINSTANCE hInstance,_In_opt_ HINSTANCE hPrevInstance,_In_ LPWSTR    lpCmdLine,_In_ int       nCmdShow)
{UNREFERENCED_PARAMETER(hPrevInstance);UNREFERENCED_PARAMETER(lpCmdLine);// TODO: 在此处放置代码。// 初始化全局字符串LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);LoadStringW(hInstance, IDC_OWNERWNDANDPARENTWND, szWindowClass, MAX_LOADSTRING);MyRegisterClass(hInstance);// 执行应用程序初始化:if (!InitInstance(hInstance, nCmdShow)){return FALSE;}HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_OWNERWNDANDPARENTWND));MSG msg;// 主消息循环:while (GetMessage(&msg, nullptr, 0, 0)){if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)){TranslateMessage(&msg);DispatchMessage(&msg);}}return (int)msg.wParam;
}//
//  函数: MyRegisterClass()
//
//  目标: 注册窗口类。
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{WNDCLASSEXW wcex;wcex.cbSize = sizeof(WNDCLASSEX);wcex.style = CS_HREDRAW | CS_VREDRAW;wcex.lpfnWndProc = WndProc;wcex.cbClsExtra = 0;wcex.cbWndExtra = 0;wcex.hInstance = hInstance;wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_OWNERWNDANDPARENTWND));wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);wcex.lpszMenuName = MAKEINTRESOURCEW(IDC_OWNERWNDANDPARENTWND);wcex.lpszClassName = szWindowClass;wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));return RegisterClassExW(&wcex);
}//
//   函数: InitInstance(HINSTANCE, int)
//
//   目标: 保存实例句柄并创建主窗口
//
//   注释:
//
//        在此函数中，我们在全局变量中保存实例句柄并
//        创建和显示主程序窗口。
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{hInst = hInstance; // 将实例句柄存储在全局变量中HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);if (!hWnd){return FALSE;}ShowWindow(hWnd, nCmdShow);g_hWnd = hWnd;//::SetWindowPos(hWnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_SHOWWINDOW);UpdateWindow(hWnd);return TRUE;
}//
//  函数: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  目标: 处理主窗口的消息。
//
//  WM_COMMAND  - 处理应用程序菜单
//  WM_PAINT    - 绘制主窗口
//  WM_DESTROY  - 发送退出消息并返回
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{switch (message){case WM_COMMAND:{int wmId = LOWORD(wParam);// 分析菜单选择:switch (wmId){case IDM_ABOUT:DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);break;case IDM_EXIT:DestroyWindow(hWnd);break;case IDB_ONE:{///此处创建一个非topmost的子窗口HWND hChildWnd = ::CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_DLGMODALFRAME, L"OWNERWNDANDPARENTWND", L"MyClildTitle", WS_VISIBLE | WS_OVERLAPPEDWINDOW, 600, 600, 200, 200, g_hWnd, NULL, hInst, nullptr);//HWND hChildWnd = ::CreateWindowExW(WS_EX_TOOLWINDOW | WS_EX_DLGMODALFRAME, L"TOPMOSTTEST", L"MyClildTitle", WS_VISIBLE | WS_OVERLAPPEDWINDOW, 800, 800, 200, 200, NULL, NULL, hInst, nullptr);DWORD err = ::GetLastError();::SetParent(hChildWnd, g_hWnd);break;}default:return DefWindowProc(hWnd, message, wParam, lParam);}}break;case WM_PAINT:{PAINTSTRUCT ps;HDC hdc = BeginPaint(hWnd, &ps);// TODO: 在此处添加使用 hdc 的任何绘图代码...EndPaint(hWnd, &ps);}break;case WM_DESTROY:PostQuitMessage(0);break;case WM_CREATE:{//CreateWindowW(L"Button", L"创建非topmost子窗口", WS_VISIBLE | WS_CHILD | BS_PUSHBUTTON, 35, 10, 200, 60, hWnd, (HMENU)IDB_ONE, hInst, NULL);HWND hChild = CreateWindowW(L"Button", L"创建子窗口", WS_VISIBLE | WS_CHILD | BS_PUSHBUTTON, 35, 10, 200, 60, hWnd, (HMENU)IDB_ONE, hInst, NULL);DWORD err = ::GetLastError();int i = 0;i++;}break;default:return DefWindowProc(hWnd, message, wParam, lParam);}return 0;
}// “关于”框的消息处理程序。
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{UNREFERENCED_PARAMETER(lParam);switch (message){case WM_INITDIALOG:return (INT_PTR)TRUE;case WM_COMMAND:if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL){EndDialog(hDlg, LOWORD(wParam));return (INT_PTR)TRUE;}break;}return (INT_PTR)FALSE;
}