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      VB.net 2010 視頻教程 VB.net 2010 視頻教程 VB.net 2010 視頻教程
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      首頁 > 編程開發 > vb >
      • vb教程之VB5.0中實現系統登錄

      • 2017-09-21 16:27 來源:未知
      ---- 一般進入系統都要登錄(如進入Windows NT),進行身份檢驗,以保證軟件的合法使用和維護,便于明確責任。我們自己開發的系統也必須保證系統使用者是合法用戶,登錄時要進行身份驗證。 

      ---- 系統登錄時一般有三次機會,超過則視為非法用戶,不讓使用系統。本程序是用VB5.0實現的,后臺數據庫是Access 97。 

      其主要源程序代碼如下: 
      Private Sub cmd_yes_Click() 
      '開始檢驗 
      Picture1.Picture = LoadPicture("trffc10b.ico") 
      times = times + 1 
      '解密 
      txt_mm.Text = invert(txt_mm.Text) 
      '查找用戶名 
      ordc_dlmmk.Recordset.FindFirst 
      "username='" & txt_bh.Text & "'" 
      If ordc_dlmmk.Recordset.NoMatch Then 
      If times < 3 Then 
      Picture1.Picture = LoadPicture("trffc10c.ico") 
      MsgBox "無此用戶,請重新輸入!", 
      vbExclamation + vbOKOnly,"提示信息" 
      Picture1.Picture = LoadPicture("trffc09.ico") 
      txt_bh.SetFocus 
      Call txt_bh_GotFocus 
      Exit Sub 
      Else 
      MsgBox "對不起,您無權使用本系統 
      ," + vbCrLf + vbCrLf + " 請與系統管理員聯系! ", 
      vbCritical + vbOKOnly, "提示信息" 
      End 
      End If 
      End If 
      If times < 3 Then 
      If Not (UCase(txt_mm.Text) 
      = UCase(Text2.Text)) Then 
      txt_mm.Text = invert(txt_mm.Text) 
      Picture1.Picture = LoadPicture("trffc10c.ico") 
      MsgBox "用戶密碼錯誤,請重新輸入!", 
      vbExclamation, "提示信息" 
      Picture1.Picture = LoadPicture("trffc09.ico") 
      txt_mm.SetFocus 
      Call txt_mm_GotFocus 
      Exit Sub 
      Else 
      Picture1.Picture = LoadPicture("trffc10a.ico") 
      MsgBox "歡迎您使用本系統!", vbInformation, "提示信息" 
      Unload Me 
      frm_welcome.Show 
      End If 
      ElseIf times = 3 Then 
      If UCase(txt_mm.Text) = UCase(Text2.Text) Then 
      Picture1.Picture = LoadPicture("trffc10a.ico") 
      MsgBox "歡迎您使用本系統!", vbInformation, "提示信息" 
      Unload Me 
      frm_welcome.Show 
      Exit Sub 
      End If 
      MsgBox "對不起,您無權使用本系統, 
      " + vbCrLf + vbCrLf + " 請與系統管理員聯系! ", 
      vbCritical + vbOKOnly, "提示信息" 
      End 
      End If 
      End Sub 

      ---- 由于一般系統用戶有多個,所以必須設置多用戶。通常用戶名和對應密碼以數據庫的形式保存。但數據庫極易暴露,可直接通過打開數據庫而獲取用戶名和密碼,安全性不好,所以應進行加密工作--保存在數據庫中的密碼與登錄時輸入的密碼不一樣,保存時進行加密,登錄時進行解密。這樣,即使看到了數據庫內容,如果不知道解密過程也無法進入系統。 

      ---- 一個比較簡單的加密過程如下: 

      Public Function invert(passw As String) 
      Dim i As Integer 
      Dim Temp As String 
      Temp = "" 
      For i = Len(passw) To 1 Step -1 
      Temp = Temp + Mid(passw, i, 1) 
      Next i 
      invert = Temp 
      End Function 

      ---- 至此一個簡單的系統登錄過程就實現了。
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