Private Declare Function ReadFile Lib "kernel32" (ByVal hFile As Long, lpBuffer As Any, ByVal nNumberOfBytesToRead As Long, lpNumberOfBytesRead As Long, lpOverlapped As OVERLAPPED) As Long
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Public Function ReadData(fhdata As String, Optional lngSize As Long = 255, Optional Outtime As Long = 2000, Optional txtRecv As TextBox) As Long
    On Error GoTo Routine_Exit                                   '打开错误陷阱


    If (com_Handle = 0) Then
        ReadData = 0
        Exit Function
    End If


    Dim lngBytesRead As Long
    Dim fReadStat As Long
    Dim lngErrorFlags As Long
    Dim lngStatus As Long
    Dim udtCommStat As COMSTAT

    '读数据
     If ClearCommError(com_Handle, lngErrorFlags, udtCommStat) <= 0 Then
        PurgeComm com_Handle, PURGE_RXABORT Or PURGE_RXCLEAR
    End If
        fhdata = Space$(255)
        
        fReadStat = ReadFile(com_Handle, ByVal fhdata, lngSize, fReadStat, m_OverlappedRead)
        txtRecv.Text = txtRecv.Text & Trim$(fhdata)
        ClearInBuf                                         '清除缓冲区
   
    ReadData = lngBytesRead
   
    Exit Function
Routine_Exit:
    ReadData = 0
End Function

谢谢，这是字节数组与字符数组转换存在问题。

五楼正解。。。