是message的意思
MSG是一个结构体
typedef struct tagMSG { // msg
HWND hwnd;
UINT message;
WPARAM wParam;
LPARAM lParam;
DWORD time;
POINT pt;
} MSG;
成员：
hwnd
Handle to the window whose window procedure receives the message.
message
Specifies the message number.
wParam
Specifies additional information about the message.The exact meaning depends on the value of the message member.
lParam
Specifies additional information about the message.The exact meaning depends on the value of the message member.
time
Specifies the time at which the message was posted.
pt
Specifies the cursor position,in screen coordinates,when the message was posted.
QuickInfo
