'先在一模块中进行API声明：
Public Declare Function GetWindowsDirectory Lib "kernel32" Alias "GetWindowsDirectoryA" (ByVal lpBuffer As String, ByVal nSize As Long) As Long
Public Declare Function GetSystemDirectory Lib "kernel32" Alias "GetSystemDirectoryA" (ByVal lpBuffer As String, ByVal nSize As Long) As Long
'注释：在程序中调用
Dim WindowsDirectory As String, SystemDirectory As String, x As Long
WindowsDirectory = Space(255)
SystemDirectory = Space(255)
x = GetWindowsDirectory(WindowsDirectory, 255)
x = GetSystemDirectory(SystemDirectory, 255)
MsgBox "Windows的安装目录是:" + WindowsDirectory+",系统目录是:" + SystemDirectory
'----------------------------------------------------------------------------------------------------------
'如何得知TextBox中文字所有的行数？
'API函数声明
Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Public Const EM_GETLINECOUNT = &HBA
' 注释：在程序中调用
LineCnt = SendMessage(ctl.hwnd, EM_GETLINECOUNT, 0, 0)
'注释：LineCnt即为此TextBox的行数。