Decimal values recognized as DateTime instead of returning false from DateTime.Parse

Question

I need to perform a check based on a string value whether its a date or decimal but date parse always return true for decimal.

string val = "3.5";
DateTime oDate = DateTime.Parse(val);

It returns a valid date 3/5/2019.

How to validate string to know its a valid date when date format is not known?

Answer 1

"How to validate string to know its a valid date?"

The issue is that "3.5" is considered a valid date (and also a decimal).

If you want the decimal type to always "win" (i.e. you don't want isDate and isDecimal to both be true), include a decimal check in your validation.

One way to do it is to use the TryParse methods (which return a bool if a string can be parsed to the type, and which sets an out parameter to the converted value) to determine if the string can be converted to a type, for example:

string val = "3.5";

// temp variables to hold parsed values
DateTime tmpDate;
decimal tmpDec;
int tmpInt;

var isDecimal = decimal.TryParse(val, out tmpDec);
var isInteger = int.TryParse(val, out tmpInt);

// When checking if it's a DateTime, make sure it's not also a decimal
var isDate = !isDecimal && DateTime.TryParse(val, out tmpDate);