Why it is not allowed to create datetime constant in .net?

Question

I want to create a datetime constant in .net but getting the error message

const DateTime dt = Convert.ToDateTime("02/02/2014"); 

'System.DateTime' cannot be declared const.

Answer 1

Even if you could declare a DateTime as const (which you can't, as other answers have indicated) you would have to use a compile-time constant as the value - and DateTime.Now most certainly isn't a compile-time constant.

This is valid though:

static readonly DateTime dt = DateTime.Now(); 

Note that this will be "whatever time the type initializer for the type ran" though. That's rarely a particularly useful value unless you ensure it's initialized on start-up, assuming that's what you're trying to measure...

Answer 2

DateTime is not a native type in the C# language - it's a struct from the .Net libraries.

In C#, you can only create consts from the native language types, and you can only initialise them with values that can be calculated at compile-time. DateTime.Now cannot be calculated at compile time.

(The only reference type you can use with a const is a string, and that's because strings are handled specially.)

See http://msdn.microsoft.com/en-gb/library/e6w8fe1b%28v=vs.71%29.aspx