对在C＃中引发异常感到困惑

Question

I using try/catch and throw to handle exceptions. So I am using try/catch is used capture errors which include problems like file is not available etc and then using throw when the text contains wrong values.

The basic layout of my Main() is as follows:

   while ((line = sr.ReadLine()) != null)
        {
            try
            {
                //get the input from readLine and saving it

                if (!valuesAreValid)
                {
                    //this doesnt make the code stop running
                    throw new Exception("This value is not wrong"); 

                 } else{
                 //write to file
                 }
            }
            catch (IndexOutOfRangeException)
            {
               //trying to throw the exception here but the code stops

            }

            catch (Exception e)
            {

               //trying to throw the exception here but the code stops 


            }

So if you notice I am throwing an exception inside try/catch and that doesnt stop the program whereas when trying to throw Exception inside the catch statement, the code stops. Does anyone have any idea how to fix this?

Answer 1

If you throw an exception inside a catch , it will not be handled by that catch . If there's no catch further up, you'll get an unhandled exception.

try {
    try {
        throw new Exception("example");
    } catch {
        throw new Exception("caught example, threw new exception");
    }
} catch {
    throw new Exception("caught second exception, throwing third!");
    // the above exception is unhandled, because there's no more catch statements
}

Answer 2

By default, unless you rethrow an exception in the catch block, the exception will stop propogating upwards at the 'catch' block where it was caught. Which means, the program will not exit.

If you don't want to catch the exception, and want the program to exit, you have two options: - remove the catch block for 'Exception' - rethrow the exception inside it's catch block.

catch (Exception e)
{
   throw e; // rethrow the exception, else it will stop propogating at this point
}

In general, unless you have some logical response to an exception, avoid catching it at all. This way you will not "hide" or suppress errors that should cause the program to error out.

Also, the MSDN documentation is a pretty good place to understand exception handling: http://msdn.microsoft.com/en-us/library/vstudio/ms229005%28v=vs.100%29.aspx

Answer 3

while ((line = sr.ReadLine()) != null)
        {
            try
            {
                //get the input from readLine and saving it

                if (!valuesAreValid)
                {
                    //this doesnt make the code stop running
                    throw new Exception("This value is not wrong"); 

                 } else{
                 //write to file
                 }
            }
            catch (IndexOutOfRangeException)
            {
               //trying to throw the exception here but the code stops

            }

            catch (Exception e)
            {

               //trying to throw the exception here but the code stops 
             throw e; 

            }

Answer 4

I'm not sure what you mean by "stop the program". The program will stop if you do not handle an exception, but your code is handling the Exception you throw via the catch (Exception e) block. Or maybe you mean that you want to exit the while loop, in which case you could use break .