値が有効かどうかを判定する

Function isval(str As String) As Boolean
    Dim ret As Boolean
    Dim ret1, ret2 As Variant
    ret1 = InStr(1, str, "#VALUE!", vbBinaryCompare)
    ret2 = InStr(1, str, "#DIV/0!", vbBinaryCompare)
    If (ret1 <> 0 And IsNull(ret1) = False) Or (ret2 <> 0 And IsNull(ret2) = False) Then
        ret = False
    Else
        ret = True
    End If
    isval = ret
End Function