vba - VBA 中 Val 函数的签名结果

Question

我在ms access中使用vba，发现如果我的参数大于0x8000小于0x10000，结果为负数

例如。 Val("&H8000") = -32768 Val("&HFFFF")= -1

如何获取无符号数？
谢谢!

Answer 1

这里有个问题:

?TypeName(&HFFFF)
Integer

Integer 类型是 16 位的，65,535 溢出了它。这可能有点矫枉过正，但写起来很有趣:

Function ConvertHex(ByVal value As String) As Double
    
    If Left(value, 2) = "&H" Then
        value = Right(value, Len(value) - 2)
    End If
    
    Dim result As Double
    
    Dim i As Integer, j As Integer
    For i = Len(value) To 1 Step -1
        
        Dim digit As String
        digit = Mid$(value, i, 1)
        
        result = result + (16 ^ j) * Val("&H" & digit)
        j = j + 1
        
    Next
    
    ConvertHex = result
    
End Function

此函数从右边开始迭代每个数字，计算其值并在它移动到最左边的数字时将其添加到结果中。

---

?ConvertHex("&H10")
 16 
?ConvertHex("&HFF")
 255 
?ConvertHex("&HFFFF")
 65535 
?ConvertHex("&HFFFFFFFFFFFFF")
 281474976710655 

---

更新

正如我所怀疑的，有更好的方法来做到这一点。 Credits to @Jonbot for this one :

Function ConvertHex(ByVal value As String) As Currency
    Dim result As Currency
    result = CCur(value)

    If result < 0 Then
        'Add two times Int32.MaxValue and another 2 for the overflow
        'Because the hex value is apparently parsed as a signed Int64/Int32
        result = result + &H7FFFFFFF + &H7FFFFFFF + 2
    End If

    ConvertHex = result
End Function