Cast null value to a type

c# casting compiler-errors null nullreferenceexception
UfukSURMEN picture UfukSURMEN · Dec 19, 2016 · Viewed 20.6k times · Source

I have a simple question. if we cast some null variable to a type. I expect compiler to throw Some Exception, but it is not. And I realy want to know the reason why. I mean

string sample1 = null as string;
string sample2 = (string)null;


object t1 = null;
TestClass t2 = (TestClass)t1;

maybe in the first one, as operator handles the exception handling. But others samples must throw exception. How compiler handles these situations , maybe since the variables are null , it does not perform cast operation? Cause if it really cast a null pointer it must be an error.

Answer

Stephan picture Stephan · Dec 19, 2016

According to the documentation (Explicit conversions) you can cast from a base type to a derived type.

Since null is a valid value for all reference types, as long as the cast route exists you should be fine.

object null → TestClass null works as object is a superclass to all reference types.

However, if you try string null → TestClass null (Assuming TestClass is not a subtype of string), you will find a compilation error as TestClass is not a derived type of string.

Related questions

Get int value from enum in C#

I have a class called Questions (plural). In this class there is an enum called Question (singular) which looks like this. public enum Question { Role = 2, ProjectFunding = 3, TotalEmployee = 4, NumberOfServers = 5, TopBusinessConcern = 6 } In the Questions class I have a get(int foo) function …

Read More
How can I cast int to enum?

How can an int be cast to an enum in C#?

Read More
String was not recognized as a valid DateTime " format dd/MM/yyyy"

I am trying to convert my string formatted value to date type with format dd/MM/yyyy. this.Text="22/11/2009"; DateTime date = DateTime.Parse(this.Text); What is the problem ? It has a second override which asks for IFormatProvider. What is …

Read More