Decimal. Parse string, postfixed by a minus sign

Question

decimal decimalVal;
Decimal.TryParse(\"123-\", out decimalVal);
Console.WriteLine(decimalVal); // -123

Why do \"123-\" string parsed this way?

Answer 1

The NumberNegativePattern is only used for string output, but ignored when parsing. For parsing, another parameter is used: NumberStyles.

Convert.ChangeType routes to decimal.Parse in your example, so if you directly used the correct overload, you can specify to not allow a trailing sign:

var result = decimal.Parse("123-", NumberStyles.Number & ~NumberStyles.AllowTrailingSign); // will throw an exception

Answer 2

This is an accepted format for Decimal.Parse. The style option to the Parse method allows for leading and trailing signs.

Read more: http://msdn.microsoft.com/en-us/library/91fwbcsb.aspx

Answer 3

NumberStyles.Number enumerator is used by default:

Indicates that the AllowLeadingWhite, AllowTrailingWhite, AllowLeadingSign, AllowTrailingSign, AllowDecimalPoint, and AllowThousands styles are used. This is a composite number style

http://msdn.microsoft.com/en-us/library/system.globalization.numberstyles.aspx

Answer 4

The Decimal.TryParse Method parses the input with NumberStyles.Number by default. NumberStyles.Number includes NumberStyles.AllowTrailingSign.

Decimal.TryParse Method (String, Decimal)

[...]
Parameter s is interpreted using the NumberStyles.Number style.
[...]

Number   Indicates that the AllowLeadingWhite, AllowTrailingWhite, AllowLeadingSign, AllowTrailingSign, AllowDecimalPoint, and AllowThousands styles are used. This is a composite number style.

AllowTrailingSign   Indicates that the numeric string can have a trailing sign. Valid trailing sign characters are determined by the NumberFormatInfo.PositiveSign and NumberFormatInfo.NegativeSign properties.