afxdata是一个全局变量，MFC用它来记录系统信息，如版本信息等。它定义在AFXIMPL.H中。
struct AUX_DATA
{
// system metrics
int cxVScroll, cyHScroll;
int cxIcon, cyIcon;
int cxBorder2, cyBorder2;
// device metrics for screen
int cxPixelsPerInch, cyPixelsPerInch;
// convenient system color
HBRUSH hbrWindowFrame;
HBRUSH hbrBtnFace;
// color values of system colors used for CToolBar
COLORREF clrBtnFace, clrBtnShadow, clrBtnHilite;
COLORREF clrBtnText, clrWindowFrame;
// standard cursors
HCURSOR hcurWait;
HCURSOR hcurArrow;
HCURSOR hcurHelp; // cursor used in Shift+F1 help
// special GDI objects allocated on demand
HFONT hStatusFont;
HFONT hToolTipsFont;
HBITMAP hbmMenuDot;
// other system information
UINT nWinVer; // Major.Minor version numbers
BOOL bWin95; // TRUE if Windows 95 (not NT)
BOOL bWin4; // TRUE if Windows 4.0
BOOL bNotWin4; // TRUE if not Windows 4.0
BOOL bSmCaption; // TRUE if WS_EX_SMCAPTION is supported
BOOL bMarked4; // TRUE if marked as 4.0
// Implementation
AUX_DATA();
~AUX_DATA();
void UpdateSysColors();
void UpdateSysMetrics();
};
extern AFX_DATA AUX_DATA afxData;