Question

Dim number As Double = 0
Dim result As Double = 0

number = -10
Try
    result = Math.Sqrt(number)

Catch ex As Exception
    MsgBox("ex = " & ex.ToString)
End Try

MsgBox("result = " & result)

运行此代码段时，我得到：result = n. def而不是捕获异常。

Answer 1

如果输入值为负as detailed here

，

Math.Sqrt不会抛出异常

但你可以在sqrt之后检查该值是否有效，如果不是

则抛出你自己的异常如果值为“Not a Number”，则

Double.IsNaN会返回True：

    Dim number As Double = 0
    Dim result As Double = 0
    number = -10
    Try
        result = Math.Sqrt(number)
        If Double.IsNaN(result) Then Throw New Exception("Square root cannot be calculated for the value " & number)
    Catch ex As Exception
        MsgBox("ex = " & ex.ToString)
    End Try

    MsgBox("result = " & result)

请注意，即使抛出异常，您仍然会显示第二个消息框，因此我建议这样的事情可能更好：

    Dim number As Double = 0
    Dim result As Double = 0
    number = -10
    Try
        result = Math.Sqrt(number)
        If Double.IsNaN(result) Then
            MsgBox("ex = " & "Square root cannot be calculated for the value " & number)
        Else
            MsgBox("result = " & result)
        End If

    Catch ex As Exception
        MsgBox("ex = " & ex.ToString)
    End Try

Answer 2

您的代码工作正常，因为没有例外可以捕获。

如MSDN documentation中所述，Math.Sqrt在传递负参数时返回Double.NaN;它会不抛出任何异常。

当前文化为德语（“de-DE”）时，

Double.NaN.ToString()将返回n. def.。

我怎么能抓住呢？ DEF＆＃39;异常（例如：负双数的Sqrt）

2 个答案: