int MessageBox(
  HWND hWnd,          // handle of owner window
  LPCTSTR lpText,     // address of text in message box
  LPCTSTR lpCaption,  // address of title of message box
  UINT uType          // style of message box
);
vcl里封装了此函数，故在窗口函数中调用时，不需要第一个HWND参数。
UINT uType的类型如下：(可以 or 起来)

Specify one of the following flags to indicate the buttons contained in the message box: Flag Meaning
MB_ABORTRETRYIGNORE The message box contains three push buttons: Abort, Retry, and Ignore.
MB_OK The message box contains one push button: OK. This is the default.
MB_OKCANCEL The message box contains two push buttons: OK and Cancel.
MB_RETRYCANCEL The message box contains two push buttons: Retry and Cancel.
MB_YESNO The message box contains two push buttons: Yes and No.
MB_YESNOCANCEL The message box contains three push buttons: Yes, No, and Cancel.



Specify one of the following flags to display an icon in the message box: Flag Meaning
MB_ICONEXCLAMATION,
MB_ICONWARNING
An exclamation-point icon appears in the message box.
MB_ICONINFORMATION, MB_ICONASTERISK
An icon consisting of a lowercase letter i in a circle appears in the message box.
MB_ICONQUESTION A question-mark icon appears in the message box.
MB_ICONSTOP,
MB_ICONERROR,
MB_ICONHAND
A stop-sign icon appears in the message box.



Specify one of the following flags to indicate the default button: Flag Meaning
MB_DEFBUTTON1 The first button is the default button.
MB_DEFBUTTON1 is the default unless MB_DEFBUTTON2, MB_DEFBUTTON3, or MB_DEFBUTTON4 is specified.

MB_DEFBUTTON2 The second button is the default button.
MB_DEFBUTTON3 The third button is the default button.
MB_DEFBUTTON4 The fourth button is the default button.



Specify one of the following flags to indicate the modality of the dialog box: Flag Meaning
MB_APPLMODAL The user must respond to the message box before continuing work in the window identified by the hWnd parameter. However, the user can move to the windows of other threads and work in those windows.
Depending on the hierarchy of windows in the application, the user may be able to move to other windows within the thread. All child windows of the parent of the message box are automatically disabled, but popup windows are not.

MB_APPLMODAL is the default if neither MB_SYSTEMMODAL nor MB_TASKMODAL is specified.

MB_SYSTEMMODAL Same as MB_APPLMODAL except that the message box has the WS_EX_TOPMOST style. Use system-modal message boxes to notify the user of serious, potentially damaging errors that require immediate attention (for example, running out of memory). This flag has no effect on the user's ability to interact with windows other than those associated with hWnd.
MB_TASKMODAL Same as MB_APPLMODAL except that all the top-level windows belonging to the current thread are disabled if the hWnd parameter is NULL. Use this flag when the calling application or library does not have a window handle available but still needs to prevent input to other windows in the calling thread without suspending other threads.



In addition, you can specify the following flags:

MB_DEFAULT_DESKTOP_ONLY
The desktop currently receiving input must be a default desktop; otherwise, the function fails. A default desktop is one an application runs on after the user has logged on.
MB_HELP
Adds a Help button to the message box. Choosing the Help button or pressing F1 generates a Help event.
MB_RIGHT
The text is right-justified.
MB_RTLREADING
Displays message and caption text using right-to-left reading order on Hebrew and Arabic systems.
MB_SETFOREGROUND
The message box becomes the foreground window. Internally, the system calls the SetForegroundWindow function for the message box.
MB_TOPMOST
The message box is created with the WS_EX_TOPMOST window style.
MB_SERVICE_NOTIFICATION

返回值含义如下：

If the function succeeds, the return value is one of the following menu-item values returned by the dialog box:

Value Meaning
IDABORT Abort button was selected.
IDCANCEL Cancel button was selected.
IDIGNORE Ignore button was selected.
IDNO No button was selected.
IDOK OK button was selected.
IDRETRY Retry button was selected.
IDYES Yes button was selected.

至于 -> 是 C系列语言中的对象指针访问成员符。当用对象访问成员时用.算符。用对象指针访问成员时必须用->算符。

这位大哥真是好啊！看来我要接着学基础了！！！