ToString on null string

c# string exception null tostring
MartW picture MartW · Jan 25, 2011 · Viewed 70.7k times · Source

Why does the second one of these produce an exception while the first one doesn't?

string s = null;
MessageBox.Show(s);
MessageBox.Show(s.ToString());

Updated - the exception I can understand, the puzzling bit (to me) is why the first part doesn't show an exception. This isn't anything to do with the Messagebox, as illustrated below.

Eg :

string s = null, msg;
msg = "Message is " + s; //no error
msg = "Message is " + s.ToString(); //error

The first part appears to be implicitly converting a null to a blank string.

Answer

Axarydax picture Axarydax · Jan 25, 2011

because you cannot call instance method ToString() on a null reference.

And MessageBox.Show() is probably implemented to ignore null and print out empty message box.

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