学生系统之用户登录：用户登录流程

第一步：获取本计算机用户名

Private Sub Form_Load()重点内容
    Dim sBuffer As String   '缓冲器
    Dim lSize As Long

    sBuffer = Space$(255)   '缓冲器容量255Byte，sBuffer为255个空格字符串
    lSize = Len(sBuffer)     'sBuffer串的长度
    Call GetUserName(sBuffer, lSize)     '读取用户名到sBuffer中

    If lSize > 0 Then
        txtUserName.Text = ""
    Else

第二步：判断文本框

Private Sub cmdOK_Click()
    Dim txtSQL As String
    Dim mrc As ADODB.Recordset
    Dim MsgText As String

    UserName = ""
    If Trim(txtUserName.Text = "") Then
        MsgBox "没有这个用户，请重新输入用户名！", vbOKOnly + vbExclamation, "警告"
        txtUserName.SetFocus
    Else
        txtSQL = "select*from user_Info where user_ID='" & txtUserName.Text & "'"
        Set mrc = ExecuteSQL(txtSQL, MsgText)

第三步：ExecuteSQL函数执行

Public Function ExecuteSQL(ByVal SQL As String, MsgString As String) As ADODB.Recordset
'execute SQL and return recordset
    Dim cnn As ADODB.Connection
    Dim rst As ADODB.Recordset
    Dim sTokens() As String

    On Error GoTo ExecuteSQL_Error

    sTokens = Split(SQL)
    Set cnn = New ADODB.Connection
    cnn.Open ConnectString

第四步：打开ConnectString，连接数据库

Public Function ConnectString() As String       '以文件DSN标记，访问ODBC数据源
ConnectString = "FileDSN=student.dsn;UID=sa;PWD=123456"      '连接文件dsn
End Function

第五步：判断增删改查

If InStr("INSERT,DELETE,UPDATE", UCase$(sTokens(0))) Then
        cnn.Execute SQL
        MsgString = sTokens(0) & " query successful"

    Else
        Set rst = New ADODB.Recordset
        rst.Open Trim$(SQL), cnn, adOpenKeyset, adLockOptimistic
        Set ExecuteSQL = rst
        MsgString = "查询到" & rst.RecordCount & "条记录"
    End If

ExecuteSQL_Exit:
    Set rst = Nothing
    Set cnn = Nothing
    Exit Function

第六步：数据库查询后的判断

If mrc.EOF Then
            MsgBox "没有这个用户，请重新输入用户名!", vbOKOnly + vbExclamation, "警告"
            txtUserName.SetFocus
        Else
            If Trim(mrc.Fields(1)) = Trim(txtPassword.Text) Then
                OK = True
                mrc.Close
                Me.Hide
                UserName = Trim(txtUserName.Text)
            Else
                MsgBox "输入密码不正确，请重新输入!", vbOKOnly + vbExclamation, "警告"
                txtPassword.SetFocus
                txtPassword.Text = ""
            End If

第七步：登录成功