C#

CSHARP.STRUCT.EXCP.EEH : Empty Exception Handler (C#)

Summary

An exception handler has an empty body.

Sometimes, an empty handler is needed since the compiler does not know that an exception will never be thrown there. If the analyzer recognizes that situation, it will not issue any warning for the empty exception handler.

This checker controls if exception handlers might be incorrect. For instance, an exception handler with an empty body might be an unfinished snippet of code; an exception handler for a very generic exception type might end up catching too many exceptions, also some that were not meant to be caught there.

Properties

Class Name Empty Exception Handler (C#)
Significance reliability
Mnemonic CSHARP.STRUCT.EXCP.EEH
Categories
CWE CWE:390 Detection of Error Condition Without Action
Availability Available for C# only.
Enabling Checks for this warning class are enabled by default. To disable them, add the following WARNING_FILTER rule to the project configuration file. 
WARNING_FILTER += discard class="Empty Exception Handler (C#)"

Example 

using System;
using System.IO;


namespace DocumentationExamples
{

    public class ExceptionHandlers
    {
        public static void Main(string[] args)
        {
            StreamWriter fw = null;
            try
            {
                fw = new StreamWriter(args[0]);
                fw.Dispose();
            }
            catch (IndexOutOfRangeException e) { }  // Empty Exception Handler (C#) warning issued here
            catch (Exception e)                     // Generic Exception Handler (C#) warning issued here
            {
                Console.WriteLine("unusual");
            }
        }
    }
}

The programmer could resolve these warnings as follows. 

public static void Main(string[] args)
{
    StreamWriter fw = null;
    try
    {
        fw = new StreamWriter(args[0]);
        fw.Dispose();
    }
    catch (IndexOutOfRangeException e) {         // resolve "Empty Exception Handler (C#)" warning by printing a message to the user
        Console.WriteLine("usage: Main filename");
    } 
    catch (IOException e)                        // resolve "Generic Exception Handler (C#)" warning by catching IOException instead of Exception
    {
        Console.WriteLine("I/O error");
    }
}

Resolution

Add a body to the exception handler, or narrow to the exception types.

Note

Sometimes, an empty handler is needed since the compiler does not know that an exception will never be thrown there. If the analyzer recognizes that situation, it will not issue any warning for the empty exception handler. For instance, in the following program:

public class CloneOK implements Cloneable {
  private int f;

  public CloneOK(int f) {
    this.f = f;
  }

  @Override
  protected Object clone() {
    CloneOK result = null;

    try {
      System.out.println("Starting cloning");
      result = (CloneOK) super.clone();
      result.f = f;
      System.out.println("Finished cloning");
    }
    catch (CloneNotSupportedException e) {
    }

    return result;
  }

  public static void main(String[] args) {
    new CloneOK(13).clone();
  }
}

This checker will not issue any warning, since the call to super.clone() is applied to a cloneable object this and will consequently never throw a CloneNotSupportedException. The programmer must nevertheless write that empty handler, since otherwise the compiler will not compile the program.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.