C# 0 The Complete Reference

PART I

C h a p t e r   1 4 :  

U s i n g   I / O  

373

PART IPART I

The exceptions 

PathTooLongException

,

DirectoryNotFoundException

, and 

FileNotFoundException

 are subclasses of 

IOException

. Thus, it is possible to catch 

all three by catching 

IOException

.

The following shows one way to open the file 

test.dat

 for input:

FileStream fin;

try {

  fin = new FileStream("test", FileMode.Open);

}

catch(IOException exc) { // catch all I/O exceptions

  Console.WriteLine(exc.Message);

  // Handle the error.

}

catch(Exception exc { // catch any other exception.

  Console.WriteLine(exc.Message);

  // Handle the error.

}

Here, the first 

catch

 clause handles situations in which the file is not found, the path is too 

long, the directory does not exist, or other I/O errors occur. The second 

catch

, which is a 

“catch all” clause for all other types of exceptions, handles the other possible errors (possibly 

by rethrowing the exception). You could also check for each error individually, reporting 

more specifically the problem that occurred and taking remedial action specific to that error.

For the sake of simplicity, the examples in this book will catch only 

IOException

, but 

your real-world code may (probably will) need to handle the other possible exceptions, 

depending upon the circumstances. Also, the exception handlers in this chapter simply 

report the error, but in many cases, your code should take steps to correct the problem when 

possible. For example, you might reprompt the user for a filename if the one previously 

entered is not found.