函数声明如下
CWnd::SetCaretPos
static void PASCAL SetCaretPos( POINT point );
注意参数个是POINT结构体
而在调用的时候是
SetCaretPos（CPoint），也就是说传递去一个CPoint对象，
结构体和类应该是两码事，可这样编译却没有出错？？
CWnd::SetCaretPos
static void PASCAL SetCaretPos( POINT point );
注意参数个是POINT结构体
而在调用的时候是
SetCaretPos（CPoint），也就是说传递去一个CPoint对象，
结构体和类应该是两码事，可这样编译却没有出错？？
class CPoint : public tagPOINT
CPoint的类是从tagPOINT也就是POINT结构派生的类。
The CPoint class is similar to the Windows POINT structure. It also includes member functions to manipulate CPoint and POINT structures. A CPoint object can be used wherever a POINT structure is used. The operators of this class that interact with a “size” accept either CSize objects or SIZE structures, since the two are interchangeable.Note This class is derived from the tagPOINT structure. (The name tagPOINT is a less-commonly-used name for the POINT structure.) This means that the data members of the POINT structure, x and y, are accessible data members of CPoint.#include <afxwin.h>摘自MSDN