SendMessage(句柄,消息,参数1,参数2) “消息的内容”说明。左边是消息，右边是十六位的ID，要转换为10进制后才可以给E用。
比如 SendMessage(文本框的句柄,13,256,一个初始化的容器)，作用就是获取文本框的内容到一个初始化的容器内。
其中的13就是 WM_GETTEXT = 0x000D。000D=13，明白？
消息的名称前面两个或三个字母是表明所对应的类或者控件类型，比如WM、EM、LB、CB、TB等。
WM_NULL = 0x0000,
WM_CREATE = 0x0001,
WM_DESTROY = 0x0002,
WM_MOVE = 0x0003,
WM_SIZE = 0x0005,
WM_ACTIVATE = 0x0006,
WM_SETFOCUS = 0x0007,
WM_KILLFOCUS = 0x0008,
WM_ENABLE = 0x000A,
WM_SETREDRAW = 0x000B,
WM_SETTEXT = 0x000C,
WM_GETTEXT = 0x000D,
WM_GETTEXTLENGTH = 0x000E,
WM_PAINT = 0x000F,
WM_CLOSE = 0x0010,
WM_QUERYENDSESSION = 0x0011,
WM_QUERYOPEN = 0x0013,
WM_ENDSESSION = 0x0016,
WM_QUIT = 0x0012,
WM_ERASEBKGND = 0x0014,
WM_SYSCOLORCHANGE = 0x0015,
WM_SHOWWINDOW = 0x0018,
WM_WININICHANGE = 0x001A,
WM_SETTINGCHANGE = 0x001A,
WM_DEVMODECHANGE = 0x001B,
WM_ACTIVATEAPP = 0x001C,
WM_FONTCHANGE = 0x001D,
WM_TIMECHANGE = 0x001E,
WM_CANCELMODE = 0x001F,
WM_SETCURSOR = 0x0020,
WM_MOUSEACTIVATE = 0x0021,
WM_CHILDACTIVATE = 0x0022,
WM_QUEUESYNC = 0x0023,
WM_GETMINMAXINFO = 0x0024,
WM_PAINTICON = 0x0026,
WM_ICONERASEBKGND = 0x0027,
WM_NEXTDLGCTL = 0x0028,
WM_SPOOLERSTATUS = 0x002A,
WM_DRAWITEM = 0x002B,
WM_MEASUREITEM = 0x002C,
WM_DELETEITEM = 0x002D,
WM_VKEYTOITEM = 0x002E,
WM_CHARTOITEM = 0x002F,
WM_SETFONT = 0x0030,
WM_GETFONT = 0x0031,
WM_SETHOTKEY = 0x0032,
WM_GETHOTKEY = 0x0033,
WM_QUERYDRAGICON = 0x0037,
WM_COMPAREITEM = 0x0039,
WM_GETOBJECT = 0x003D,
WM_COMPACTING = 0x0041,
WM_COMMNOTIFY = 0x0044,
WM_WINDOWPOSCHANGING = 0x0046,
WM_WINDOWPOSCHANGED = 0x0047,
WM_POWER = 0x0048,
WM_COPYDATA = 0x004A,
WM_CANCELJOURNAL = 0x004B,
WM_NOTIFY = 0x004E,
WM_INPUTLANGCHANGEREQUEST = 0x0050,
WM_INPUTLANGCHANGE = 0x0051,
WM_TCARD = 0x0052,
WM_HELP = 0x0053,
WM_USERCHANGED = 0x0054,
WM_NOTIFYFORMAT = 0x0055,
WM_CONTEXTMENU = 0x007B,
WM_STYLECHANGING = 0x007C,
WM_STYLECHANGED = 0x007D,
WM_DISPLAYCHANGE = 0x007E,
WM_GETICON = 0x007F,
WM_SETICON = 0x0080,
WM_NCCREATE = 0x0081,
WM_NCDESTROY = 0x0082,
WM_NCCALCSIZE = 0x0083,
WM_NCHITTEST = 0x0084,
WM_NCPAINT = 0x0085,
WM_NCACTIVATE = 0x0086,
WM_GETDLGCODE = 0x0087,
WM_SYNCPAINT = 0x0088,
WM_NCMOUSEMOVE = 0x00A0,
WM_NCLBUTTONDOWN = 0x00A1,
WM_NCLBUTTONUP = 0x00A2,
WM_NCLBUTTONDBLCLK = 0x00A3,
WM_NCRBUTTONDOWN = 0x00A4,
WM_NCRBUTTONUP = 0x00A5,
WM_NCRBUTTONDBLCLK = 0x00A6,
WM_NCMBUTTONDOWN = 0x00A7,
WM_NCMBUTTONUP = 0x00A8,
WM_NCMBUTTONDBLCLK = 0x00A9,
WM_NCXBUTTONDOWN = 0x00AB,
WM_NCXBUTTONUP = 0x00AC,
WM_NCXBUTTONDBLCLK = 0x00AD,