Section 16.5. The try and catch Statements

16.5. The try and catch Statements

As you saw, the exception in your previous example stopped your program dead. That's usually not the desired behavior. What you need is a way to tell the compiler, "If any exceptions are thrown in this section of code, take this action." That way, your program can continue on from the error, or at least end gracefully. This process is called handling the exception. To handle exceptions, take the following steps:

1. Execute any code that you suspect might throw an exception (such as code that opens a file or allocates memory) within a TRy block.

2. Catch any exceptions that are thrown in a catch block.

A try block is created using the keyword try and is enclosed in braces. The try block is the area of code where you want to watch for exceptions. A catch block holds the code where you take action based on the type of exception thrown. It is created using the keyword catch and is also enclosed in braces. Example 16-2 illustrates these constructs. Note that Example 16-2 is identical to Example 16-1 except that now the program includes a TRy / catch block.

Example 16-2. Try and catch blocks

 using System; namespace TryAndCatchBlocks {    class Tester    {       static void Main(  )       {          Console.WriteLine( "Enter Main..." );          Tester t = new Tester(  );          t.Run(  );          Console.WriteLine( "Exit Main..." );       }       public void Run(  )       {          Console.WriteLine( "Enter Run..." );          Func1(  );          Console.WriteLine( "Exit Run..." );       }       public void Func1(  )       {          Console.WriteLine( "Enter Func1..." );          Func2(  );          Console.WriteLine( "Exit Func1..." );       }       public void Func2(  )       {          Console.WriteLine( "Enter Func2..." );          try          {             Console.WriteLine( "Entering try block..." );             throw new ApplicationException(  );             // this code never executes because of the exception             Console.WriteLine( "Exiting try block..." );          }          catch          {             Console.WriteLine( "Exception caught and handled!" );          }          Console.WriteLine( "Exit Func2..." );       }    } } 

The output looks like this:

 Enter Main...     Enter Run...     Enter Func1...     Enter Func2...     Entering try block...     Exception caught and handled!     Exit Func2...     Exit Func1...     Exit Run...     Exit Main... 

Following the try statement is the catch statement. In a real catch statement, you might silently fix the problem (for example, by retrying a database connection), or you might interact with the user to solve the problem (such as offering the user the opportunity to close other applications and free up memory). In Example 16-2, the catch statement simply reports that the exception has been caught and handled.

Notice that the exit statements are now written. With the exception handled, execution resumes immediately after the catch block.