c++ 创建一个子窗口并根据主窗口句柄在主窗口中居中显示

下面是一个基本的C++程序，它使用Win32 API创建一个子窗口并将其居中放置在主窗口中。这个程序假设你已经有了一个主窗口的句柄（在代码中称为hParent）和一个子窗口的类名（在代码中称为szChildClass）。

#include <windows.h>

LRESULT CALLBACK ChildWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    // Register the child window class
    WNDCLASS wc = { 0 };
    wc.lpfnWndProc = ChildWndProc;
    wc.hInstance = hInstance;
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszClassName = "MyChildClass";
    RegisterClass(&wc);

    // Create the child window
    HWND hChild = CreateWindow("MyChildClass", "My Child Window", WS_VISIBLE | WS_BORDER | WS_CHILD, 0, 0, 200, 200, hParent, NULL, hInstance, NULL);

    // Center the child window in the parent window
    RECT rcParent, rcChild;
    GetWindowRect(hParent, &rcParent);
    GetWindowRect(hChild, &rcChild);
    int cxParent = rcParent.right - rcParent.left;
    int cyParent = rcParent.bottom - rcParent.top;
    int cxChild = rcChild.right - rcChild.left;
    int cyChild = rcChild.bottom - rcChild.top;
    int x = (cxParent - cxChild) / 2 + rcParent.left;
    int y = (cyParent - cyChild) / 2 + rcParent.top;
    SetWindowPos(hChild, NULL, x, y, 0, 0, SWP_NOSIZE | SWP_NOZORDER);

    // Enter the message loop
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}

LRESULT CALLBACK ChildWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }

    return 0;
}

请注意，此代码只是基本的示例。如果你想要更多的控制，你可能需要在创建子窗口之前设置更多的窗口样式和扩展样式，或者在子窗口过程中处理更多的消息。