[求助]一段登陆代码读不懂
下面是一段登陆时自动加载用户名的代码（我想是这样的）：
代码如下： 有些看不懂，请读帖子的人 帮我 “详细”讲解一下，先谢了！
Private Declare Function GetUserName Lib "advapi32.dll" Alias "GetUserNameA" (ByVal lpbuffer As String, nSize As Long) As Long
Public OK As Boolean
————————————————————————————————————————————————————
Private Sub Form_Load()
Dim sBuffer As String
Dim lSize As Long
sBuffer = Space$(255)
lSize = Len(sBuffer)
Call GetUserName(sBuffer, lSize)
If lSize > 0 Then
txtUserName.Text = Left$(sBuffer, lSize)
Else
txtUserName.Text = vbNullString
End If
End Sub
