Question

I have the need to format a decimal number as currency but I do not wish for any rounding to occur in the process.

For example (example culture is en-US)

Dim money = 1234.556789D
money.ToString("C") ' Yields $1,234.56 (notice the rounding & truncating)

money.ToString("C99") ' Yields $1,234.556789000000000000....0 -- close but not perfect, those trailing zeros are unwanted.

' I want something that would result in this...
money.ToString("??") ' Yields $1,234.56789

' likewise....
money = 0.1D
money.ToString("??") ' Yields $0.10  (notice that it at least matches the culture's currency format -- two decimal places)

Assuming all of the users of this application would be using en_US rules I could make that “??” be something hard-coded like “$#,##0.00################################################################” — but that makes my stomach churn. Is there a built-in way to accomplish what I’m after?

Answer 1

Seeing that there doesn’t seem to be a built-in way of doing this, I ended up rolling my own extension method that looks like…

Public Function ToUnroundedCurrency(ByVal value As Decimal) As String
    Dim valueAsString As String = value.ToString() ' Some loss of precision happens here, but it is not a concern.

    Dim decimalLocation As Integer = valueAsString.IndexOf(".")

    ' Get number of digits after the decimal place in the number
    Dim numberOfDecimalPlaces As Integer = 0
    If (decimalLocation > 0) Then numberOfDecimalPlaces = valueAsString.Length - decimalLocation - 1

    ' The currency formatter has a limit of 99 decimal places -- due to the decimal -> ToString() conversion above, this will never happen, but being defensive anyway.
    If (numberOfDecimalPlaces > 99) Then
        numberOfDecimalPlaces = 99
    ElseIf (numberOfDecimalPlaces < CultureInfo.CurrentCulture.NumberFormat.CurrencyDecimalDigits) Then
        ' also make sure we at least have the minimum required decimal places
        numberOfDecimalPlaces = CultureInfo.CurrentCulture.NumberFormat.CurrencyDecimalDigits
    End If

    Return value.ToString("C" & numberOfDecimalPlaces)
End Function

I noted some negligible loss of precision. We (or anybody probably) wouldn’t be dealing with decimal values fractional enough enough to ever run into the limitations.