c++ - 是否可以在 MessageBox() 中显示 HWND->i？

Question

我正在使用以下代码获取 HWND->i 但是当我启动程序时它终止并显示对话框“Program.exe 遇到问题需要关闭”:

#include <windows.h>
#include <sstream>

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

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
     static TCHAR szAppName[] = TEXT ("Program") ;
     HWND         hwnd ;
     MSG          msg ;
     WNDCLASS     wndclass ;

     wndclass.style         = CS_HREDRAW | CS_VREDRAW ;
     wndclass.lpfnWndProc   = WndProc ;
     wndclass.cbClsExtra    = 0 ;
     wndclass.cbWndExtra    = 0 ;
     wndclass.hInstance     = hInstance ;
     wndclass.hIcon         = LoadIcon (NULL, IDI_APPLICATION) ;
     wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
     wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
     wndclass.lpszMenuName  = NULL ;
     wndclass.lpszClassName = szAppName ;

     if (!RegisterClass (&wndclass))
     {
          MessageBox (NULL, TEXT ("Error"), szAppName, MB_ICONERROR) ;
          return 0 ;
     }
     hwnd = CreateWindow (szAppName,
                          TEXT ("Program"),
                          WS_OVERLAPPEDWINDOW,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          NULL,
                          NULL,
                          hInstance,
                          NULL) ;

     ShowWindow (hwnd, iCmdShow) ;

     std::ostringstream oss;
     oss << hwnd->i;
     //MessageBox(NULL, oss.str().c_str(), TEXT("message"), MB_OK);

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

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
     switch (message)
     {
     case WM_DESTROY:
          PostQuitMessage (0) ;
          return 0 ;
     }
     return DefWindowProc (hwnd, message, wParam, lParam) ;
}

当我注释掉

oss << hwnd->i;

程序运行正常。

那么，有没有办法在MessageBox()中显示hwnd->i？

Answer 1

正如 MSDN here 中所说:

Windows are objects — they have both code and data — but they are not C++ classes. Instead, a program references a window by using a value called a handle. A handle is an opaque type. Essentially, it is just a number that the operating system uses to identify an object. You can picture Windows as having a big table of all the windows that have been created. It uses this table to look up windows by their handles. (Whether that's exactly how it works internally is not important.) The data type for window handles is HWND, which is usually pronounced "aitch-wind." Window handles are returned by the functions that create windows: CreateWindow and CreateWindowEx.

最重要的是，这条评论:

Keep in mind that handles are not pointers. If hwnd is a variable that contains a handle, attempting to dereference the handle by writing *hwnd is an error.

要点是 HWND 只是您传递给处理窗口的 API 调用的东西。它的内部实现是隐藏的，与开发人员无关。通过调用 HWND->i，您试图取消引用它，就好像它是一个指针，但事实并非如此。因此你崩溃了。