throw

Question

In an exception handling we use try and catch. In some occasion in addition to try and catch we use throw as well. Could you tell me please when throw is necessary?

Maha · Answer

Thank you for your explanation.

Vulpes · Answer

In this case yes. However in general the try/catch which finally handles a re-thrown exception just needs to be in a method higher up the call stack. As the Main() method is the first method called it's always at the top of the call stack. Where you have nested try/catch statements in the same method and an exception is rethrown from an 'inner' catch it can also be caught in an 'outer' try/catch without the need to look for a suitable try/catch higher up the call stack.

Maha · Answer

So that  throw  is merely use to handle the exception in the Main() method.

Vulpes · Answer

Here's a simple example of using the 'throw' keyword. Notice that by allowing the try/catch in the Main() method to handle the exception you don't need to repeat the code in the catch block of the Divide() method: using System; class Test { static void Main() { int a = 4 b = 2 c; try { c = a/b; Console.WriteLine(a = {0} b = {1} c = {2} a b c); // no problem b = 0; // problem now c = Divide(a b); Console.WriteLine(c); } catch(DivideByZeroException ex) { Console.WriteLine(a = {0} b = {1} a b); Console.WriteLine(ex.Message); } Console.ReadKey(); } static int Divide(int x int y) { int z; try { z = x/y; } catch(DivideByZeroException) { throw; // let try/catch in Main() method handle this exception } return z; } } The output is: a = 4 b = 2 c = 2 a = 4 b = 0 Attempted to divide by zero.

Vulpes · Answer

You use 'throw' when you want to rethrow an exception that you've caught so that it can handled by some higher level try/catch block rather than by the present catch clause. Check this link for more detail: http://msdn.microsoft.com/en-us/library/1ah5wsex(v=vs.71).aspx