type in brackets eg. (string)

Question

Hello I'm new here also in programming. I have a question which i couldn't find an answer to. What does it mean when a type is written in brackets e.g. (string)e.Data.GetData(DataFormats.FileDrop) is it something like Convert.ToString()? Thank you.

Vulpes · Answer

Sorry one thing I said in my previous post was wrong. You don't in fact get an exception when obj is null if you use a cast. So this works fine and sets 's' to null: string s = (string)obj; // doesn't throw an exception if obj is null. The difference between a cast and using 'as' is that if you're casting an object which isn't a string but something else then the cast will throw an InvalidCastException but 'as' will simply return null. So: object obj = 3; // obj contains an int string s = (string)obj; // throws an exception string t = obj as string; // doesn't throw an exception t is set to null string u = Convert.ToString(obj); // doesn't throw an exception u is set to 3 Notice that the Convert.ToString() method is happy with any argument - it just calls the ToString() method of the argument's underlying type internally.

Vulpes · Answer

When the type is written in brackets like that then it's what's called a 'cast'. So in your example you're taking an expression which has a return type of object (but is really a string) and casting it to its string value. This is similar to using the Convert.ToString(object) method. However if the object is null then the latter returns an empty string. In contrast when you use a cast you will get an exception ** . There is however a form of cast (using the 'as' keyword) which doesn't throw an exception but returns null. So: string s = (string)obj; // throws an exception if obj is null ** string t = obj as string; // doesn't throw an exception if obj is null string u = Convert.ToString(obj); // doesn't throw an exception either ** WRONG - see my next post

Zygis · Answer

Thanks for a quick reply.