Question

Here’s my problem (for en-US):

Decimal.Parse("1,2,3,4") returns 1234, instead of throwing an InvalidFormatException.

Most Windows applications (Excel en-US) do not drop the thousand separators and do not consider that value a decimal number. The same issue happens for other languages (although with different characters).

Are there any other decimal parsing libraries out there that solve this issue?

Thanks!

Answer 1

I ended up having to write the code to verify the currency manually. Personally, for a framework that prides itself for having all the globalization stuff built in, it’s amazing .NET doesn’t have anything to handle this.

My solution is below. It works for all the locales in the framework. It doesn’t support Negative numbers, as Orion pointed out below, though. What do you guys think?

    public static bool TryParseCurrency(string value, out decimal result)
    {
        result = 0;
        const int maxCount = 100;
        if (String.IsNullOrEmpty(value))
            return false;

        const string decimalNumberPattern = @"^\-?[0-9]{{1,{4}}}(\{0}[0-9]{{{2}}})*(\{0}[0-9]{{{3}}})*(\{1}[0-9]+)*$";

        NumberFormatInfo format = CultureInfo.CurrentCulture.NumberFormat;

        int secondaryGroupSize = format.CurrencyGroupSizes.Length > 1
                ? format.CurrencyGroupSizes[1]
                : format.CurrencyGroupSizes[0];

        var r = new Regex(String.Format(decimalNumberPattern
                                       , format.CurrencyGroupSeparator==" " ? "s" : format.CurrencyGroupSeparator
                                       , format.CurrencyDecimalSeparator
                                       , secondaryGroupSize
                                       , format.CurrencyGroupSizes[0]
                                       , maxCount), RegexOptions.Compiled | RegexOptions.CultureInvariant);
        return !r.IsMatch(value.Trim()) ? false : Decimal.TryParse(value, NumberStyles.Any, CultureInfo.CurrentCulture, out result);
    }

And here’s one test to show it working (nUnit):

    [Test]
    public void TestCurrencyStrictParsingInAllLocales()
    {
        var originalCulture = CultureInfo.CurrentCulture;
        var cultures = CultureInfo.GetCultures(CultureTypes.SpecificCultures);
        const decimal originalNumber = 12345678.98m;
        foreach(var culture in cultures)
        {
            var stringValue = originalNumber.ToCurrencyWithoutSymbolFormat();
            decimal resultNumber = 0;
            Assert.IsTrue(DecimalUtils.TryParseCurrency(stringValue, out resultNumber));
            Assert.AreEqual(originalNumber, resultNumber);
        }
        System.Threading.Thread.CurrentThread.CurrentCulture = originalCulture;

    }