快速获得Richtextbox控件指定行文本的方法

通常我们要获得EDIT编辑框的某一行的文本,只要用sendmessage发送EM_GETLINE消息就可以了，然而当我们试图发送EM_GETLINE消息给Richtextbox控件时，却得不到正确的数据，这在Richtextbox控件同时包含中文和英文时表现的很明显，而如果Richtextbox控件的内容只有英文时，发送EM_GETLINE消息则可以得到正确的数据（写到这里，不由得开始羡慕米国人不需要同unicode打交道）。

我的做法是发送EM_GETTEXTRANGE消息给Richtextbox控件，代码如下：

Option Explicit

Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA" _
  (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
  lParam As Any) As Long
 
Private Const GTL_NUMBYTES = 16&
Private Const EM_LINEINDEX = &HBB
Private Const EM_GETLINECOUNT = &HBA
Private Const EM_LINELENGTH = &HC1
Const WM_USER = &H400
Const EM_GETTEXTRANGE = (WM_USER + 75)
Private Type CHARRANGE   'cr
    cpMin As Long
    cpMax As Long
End Type
Private Type TEXTRANGE
  chrg As CHARRANGE
  lpstrText As String ' alloca