MessageBox (NULL, TEXT ("Hello World"), TEXT ("Hello2"), MB_OK);

MessageBox函数原型如下：
int MessageBox (HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType);
第1个参数是顶层窗口的句柄，它是消息窗口的父窗口。目前我们把这个参数置为NULL，因为Hello2还没有任何其它窗口。第2个参数是准备显示在窗口里的文字。注意传入的字符串是用TEXT宏包裹的，确保它能够编译成Unicode版本。第3个参数lpCaption是显示在窗口标题栏的文字。最后一个参数uType是一系列标志位，规定消息框如何显示在屏幕上。标志位规定了消息框中按扭的数量和类型，规定了图标的类型以及消息框窗口的风格设置。

表1-1列出了Windows CE下有效的标志位
表1-1: 默认标志位

标志位 按钮或者图标

用于按钮

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MB_OK OK

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MB_OKCANCEL OK and Cancel

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MB_RETRYCANCEL Retry and Cancel

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MB_YESNO Yes and No

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MB_YESNOCANCEL Yes, No, and Cancel

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MB_ABORTRETRYIGNORE Abort, Retry, and Ignore

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用于图标

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MB_ICONEXCLAMATION, MB_ICONWARNING Exclamation point

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MB_ICONINFORMATION, MB_ICONASTERISK Lower case i within a circle

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MB_ICONQUESTION Question mark

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MB_YESNO Yes and No

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MB_ICONSTOP, MB_ICONERROR, MB_ICONHAND Stop sign

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MB_DEFBUTTON1First button

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MB_DEFBUTTON2 Second button

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MB_DEFBUTTON3 Third button

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For Window Styles:

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MB_SETFOREGROUND Bring the message box to the foreground.

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MB_TOPMOST Make the message box the topmost window.

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MessageBox的返回值指出用户按了哪个按扭。

返回值如下：

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IDOK OK button pressed

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IDYES Yes button pressed

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IDNO No button pressed

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IDCANCEL Cancel button pressed or Esc key pressed

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IDABORT Abort button pressed

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IDRETRY Retry button pressed

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IDIGNOREIgnore button pressed