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How to avoid catching generic exceptions

In my processing I would like to log any error along with the user and code details and proceed on with my work.
I am currently using a try catch block which includes a generic catch, but is catching a generic exception is a bad thing? Such as the exception could be a stackoverflowexception or outofmemoryexception and need to be handled differently.. .
But I am not sure how to avoid catching these fatal exceptions. I am looking for suggestions.
Why I want to catch all exceptions
Because I don't want a failure in one form's processing to affect the others in the loop.
Why I am catching specific exceptions:
I understand I can look for stackoverflowexception, outofmemoryexception etc... but my point is, there could be many of them...looking for each and every would make my code lengthy. I am not sure if that is the best process.

But I am not sure how to avoid catching these fatal exceptions
Well, 2 things.
First, you can always rethrow them, for example, after logging.
Second, you can catch every exception you want and if you do not catch System.Exception then all you do not catch will bubble up - that is C# 101 for beginners, so if you have a problem with that, back to reading the documentation about exceptions in general.

Exceptions cascade down. If you want to handle certain exceptions differently, implement a different catch block.
try
{
ThisMethodMayThrowException();
}
catch(StackOverflowException ex)
{
//handle a StackOverFlowException
}
catch(OutOfMemoryException ex)
{
//handle a OutOfMemoryException
}
catch(Exception ex)
{
//handle all other types.
}
In general though, you should only plan to handle expected exceptions. For example, if you're writing to a file that you expect to exist, you might anticipate a FileNotFoundException. If you tried to handle every possible exception, your code would become quite long and unwieldy, to little benefit.
Microsoft provides excellent info on exception handling.

Reverse your thinking... because the advice catching generic exception is being misinterpreted.
Handle all exceptions which are known explicitly (do the log and continue processing), but always have a generic catch all exception handler to stop all processing and handle that unknown.
In your example an overflow exception could comprise data or let malicious actors take over the system in unexpected ways; hence continuing on, should not be done.

If you know all the exceptions you want to catch, you write a catch block for each specifically:
try
{
}
catch (IOException)
{
}
catch (InvalidCastException)
{
}
...
Then all the ones you don't want to catch (and thus allow to potentially take down your program) will keep bubbling up.

I am currently using a try catch block which includes a generic catch,
but I have heard from many people that catching generic exception is a
bad thing(as the exception could be a stackoverflowexception or
outofmemoryexception).
You should know which Exception types your method calls might throw.
It could be discovered either at the Method documentation, example:
/// <exception cref="DivideByZeroException">Why it's thrown.</exception>
public void MethodThatMightThrowDivideByZeroException(){...}
or by looking at the Method code, example:
throw new DivideByZeroException();
That way, you would be able to catch it easily:
try
{
ThisMethodMayThrowException();
}
catch(DivideByZeroException ex)
{
//handle a DivideByZeroException
}

Why Throw An Exception Rather Than Letting The Code Throw It?

I want the code calling a function to handle any exception raised in the function. If I write:
try
{
// Code than may raise an exception
}
catch
{
throw;
}
The exception will be passed back with the callstack. Could I write the following instead and get the same result? Is there any reason to use the try catch in this case?
// Code that may raise an exception

In the scenario you've presented, the only reason to catch, and then rethrow, the exception, is if you're doing something else in the catch block, like logging or cleanup. Otherwise, it's entirely a no-op.
Good on you that you're using throw, rather than throw e, by the way, if you do need this construct. The former preserves the callstack; the latter does not.

There is no reason to use try/catch in that case.
If you were logging any information or encapsulating the exception in a higher-level one, then the try/catch would be indicated.

C# Error handling catch blocks

Why is it adviced most of the time that we should not trap errors like "Exception" but trap errors that we expect as developers.
Is there a performance hit in trapping generic errors or is it recommended from a best practice point of view?
try
{
// Do something
}
catch(Exception e)
{
//Log error
}

The best practice is to catch specific exception first and then move on to more generic ones.
Exception Handling (C# Programming Guide)
Multiple catch blocks with different exception filters can be chained
together. The catch blocks are evaluated from top to bottom in your
code, but only one catch block is executed for each exception that is
thrown. The first catch block that specifies the exact type or a base
class of the thrown exception is executed. If no catch block specifies
a matching exception filter, a catch block that does not have a filter
is selected, if one is present in the statement. It is important to
position catch blocks with the most specific (that is, the most
derived) exception types first.
For your question:
Why is it adviced most of the time that we should not trap errors like
"Exception" but trap errors that we expect as developers.
An example would be to catch NullReferenceException. Its never a better practice to catch NullReferenceException, instead one should always check for object being null before using its instance members. For example in case of string.
string str = null;
try
{
Console.WriteLine(str.Length)
}
catch(NullReferenceException ne)
{
//exception handling.
}
instead a check should be in place for checking against null.
if(str != null)
Console.WriteLine(str.Length);
EDIT:
I think I got the question wrong, If you are asking which exception should be caught and which shouldn't then IMO, those exceptions which can be dealt with should be caught and rest should be left in the library so they can bubble up to upper layer where appropriate handling would be done. An example would be Violation of Primary key constraint. If the application is taking input(including primary key) from the user and that date is being inserted into the database, then that exception can be caught and a message can be shown to user "Record already exists" and then let the user enter some different value.
But if the exception is related to the foreign key constraint (e.g. Some value from the dropdown list is considered invalid foreign key) then that exception should bubble up and a generic exception handler should log it in appropriate place.
For example in ASP.Net applications, these exception can be logged in Application_Error event and a general error page can be shown to the user.
EDIT 2:
For the OP's comment:
if at a low level if there would be a performance degeradation in
catching a generic error inspite of knowing if the error is
sqlexception
Even if there is going to be any performance difference it should be negligible. But Catch the specific exception, if you know that the exception is going to be SqlException then catch that.

You should only catch exceptions what you can handle. Exception is too generic so most of the time you cannot say you can handle that. It is a little funny but you should only catch exception that you except :)
There are situation when you need to catch Exception but rare and you should avoid it most of the time. Usually it indicates some design problem.

Check Eric Lippert's blog (Vexing exceptions) about best way to handle exceptions.
• Don’t catch fatal exceptions; nothing you can do about them anyway, and trying to generally makes it worse.
• Fix your code so that it never triggers a boneheaded exception – an "index out of range" exception should never happen in production code.
• Avoid vexing exceptions whenever possible by calling the “Try” versions of those vexing methods that throw in non-exceptional circumstances. If you cannot avoid calling a vexing method, catch its vexing exceptions.
• Always handle exceptions that indicate unexpected exogenous conditions; generally it is not worthwhile or practical to anticipate every possible failure. Just try the operation and be prepared to handle the exception.

Using exception handling more often than required is infact a lazy way of programming more than anything. Say you have a DataTable and you want to access the first row.
public DataRow AccessFirstRow(DataTable dt)
{
try
{
return dt.Rows[0];
}
catch (Exception e)
{
//There isn't a first row or dt is null
}
}
Instead of
public DataRow AccessFirstRow(DataTable dt)
{
if(dt != null)
if(dt.Rows.Count > 0)
return dt.Rows[0];
//If we can't access dt, then don't
return null;
}
My rule of thumb is:
Exceptions should only be used in EXCEPTION-al circumstances.
If you do decide to handle them though, as mentioned handle specific exceptions you know you might encounter instead of generic exceptions.

It's a best practice thing. The idea is that you should quickly handle the known exceptions explicitly while having more general ones higher up in the program as unexpected exceptions are likely caused by some more major/fundamental error.

Catch those exceptions which you intend to handle. You will usually want to handle particular exception in such context (method) where you have enough information for dealing with error reported (e.g. access to objects used for clean-up).
If code within try block throws different types of exceptions, you might want to handle some exceptions within the same method and re-throw others in order to handle them in the caller method (as in that context you have resources for handling those exceptions).

What should be the best Exception Handling Strategy

I am working on application where user invokes a method from UI , on this I am calling a method from business class which calls another methods
UI--> Method1 -->Method2 --> Method3
I want to display the error message to user if any exception occurs in any of the method.
Shall I go with throwing the exception directly to the caller method and at the UI layer I will catch exception and display the message.
Apart from Throwing exceptions and catching it at caller is there any better way to handle it?
I do not want to use the C++ convention where integer is returned as the result.

If you can't recover from the exception in the method where the exception happens, don't try to catch it (unless you want to log it, in which case throw it again after logging). Then catch at the UI-level.
Trying to catch exceptions at every level just adds bloat to your code.

Given your example of UI--> Method1 -->Method2 --> Method3, I would make sure that the UI has a try/catch, but then none of the other methods should catch exceptions unless they can handle them without re-throwing. And even if they handle the exception, you should question whether that exception should happen in the first place. If you handle an exception and go about your merry way, then that exception is part of your normal process flow which is a serious code smell.
Here are my recommendations:
1) Put your exception handling code in all your UI events, and then have the actual action farmed off to some other method. Don't scatter exception handling code all over the place. It's clunky and makes the code hard to read.
protected void Button1_Click(object sender, EventArgs e) {
try {
DoSomething();
}
catch Exception e {
HandleError(e);
}
}
2) Don't do this. You'll lose your stack trace and the next developer who maintains your code will hunt you down.
try {
DoSomething();
}
catch Exception e {
throw e; // don't rethrow!!!
}
If you aren't going to handle the exception, don't catch it. Or, use a naked throw like this:
try {
DoSomething();
}
catch SomeException e {
HandleException(e);
}
catch {
throw ; // keep my stack trace.
}
3) Only throw exceptions in exceptional circumstances. Don't have try/catch blocks as part of your normal process flow.
4) If you're going to throw an exception, don't ever throw a System.Exception. Derive an exception object and throw it. I often just a generic BusinessException class. This way, users of your code can determine what exceptions you made up and which ones are system/environment related.
5) Throw ArgumentException, ArgumentNullException, or ArgumentOutOfRangeException if a method caller violates the contract (preconditions) of your method. If you catch one of these, it's a programming bug. A user should never see these exceptions.
If you remember that exceptions should be a very rare occurrence and that handling them is almost always a UI concern (so the bulk of your try/catch code should stay at the UI level) you will do well.

The basic rule is "Don't catch exceptions when you cannot handle it." So any unexpected exception should ultimately tell the user that something went wrong and shut down the application as gracefully as possible. Not shutting down the application is risky because the state might be corrupted and in turn corrupt information important to the user.
Robust applications are modular so that the application can recover without shutting down by stopping or restarting single components like services or plugins.
There are some cases where you might want to catch exceptions that you cannot handle but then the exception should either be re-thrown or a new exception should be thrown.
If you want to log exceptions you will catch, log and re-throw.
If you want to improve the error message you will catch, wrap in a new exception, and throw. For example you may want to wrap a generic FileNotFoundException when reading a file in a new exception with a more descriptive message telling the user what file could not be found.

Whatever you decide - be consistent. 30 days from now yourself (or another developer) will need to understand your code.
Also, as Scott Hanselman likes to quote on his podcast (and I think it might be in the Beautiful Code book) -
All problems in computer science can be solved by another level of indirection," is a famous quote attributed to Butler Lampson, the scientist who in 1972 envisioned the modern personal computer.
Throwing exceptions is expensive. And I like to have my business layer have its own specialized exception that only it can throw. That way it makes it easier to track it down. For example (off the top of my head since I do not have a C# compiler in front of me):
public class MyException : Exception
{
private MyException(Exception ex, string msg) {
this.Message = msg;
this.InnerException = ex;
}
internal static MyException GetSomethingBadHappened(Exception ex, string someInfo) {
return new MyException(ex, someInfo);
}
}

As a rule of thumb, exceptions should only be used for exceptional cases. That is, if you expect a method call to fail sometimes, you shouldn't use exceptions. If there are several possible outcomes, you could use an enumeration:
public enum AddCustomerResult
{
Success,
CustomerAlreadyExists,
CustomerPreviouslyRetired
}
You'd still get exceptions thrown, for database-unavailable errors, and the like; but you'd be testing for expected (albeit possibly rare) cases and indicating success/failure/etc as required.
This is just one technique that works well for me.
With exceptions you want to throw them in exceptional circumstances and anywhere where there is a layer traversal (my own convention, don't know how correct it is) you'd want to catch exceptions and rethrow with a custom wrapper class for that layer.
For example, in the DAL you'd want to catch exceptions and rethrow them as an inner exception on a DataAccessException perhaps; on a web service you'd wrap all your methods in exception handlers to rethrow with a MyWebServiceException. At the UI (which traverses the from inside the app to the user's screen) you'd want to catch, log and give them a nice message. As far as I can see no reason to catch or rethrow anywhere else.
It gives you an opportunity to hide the underlying exception (which you likely don't want to expose to the caller: e.g. database errors), log in centrally, and provide a common repeatable failure mode.
In your example, you'd catch exceptions at the UI level only; because if a UI operation fails you don't want the app to crash out with an unhandled exception.
Hope that helps!

When you design a multi-tier application, you should keep in mind that those tiers can be distributed, maybe hosted within different services on different machines, thus making it necessary to throw exceptions through remote boundaries which is not a very preferable way to do.
In such a case, catching them and just bubbling some sort of error message or code is a better way in my opinion. Additionally you should allways trace the exception when you catch it. Its always good to know whats going on in your application.

It almost always pays to separate exception handling and error reporting.
Catch exceptions where it makes sense to catch them, where you have enough context to know what exactly happened and how to recover - inside Method1..3. On catching known exception, push a record to the error log.
After completing operation or step UI level can check error log and present message of "Following errors occurred: ...".

How often should I use try and catch in C#?

When writing a C# application whose #1 priority is to never crash, how often should I used a try-catch block?
Can I encapsulate all the statements in a method in try-catch blocks?
public void SomeMethod()
{
try
{
// entire contents of the function
// library calls
// function calls
// variable initialization .. etc
}
catch (Exception e)
{
// recover
}
}
What are the downsides to wrapping everything in try-catch blocks?

The only down side is when an exception is actually thrown. There is no overhead for wrapping the code, except for when exceptions occur.
Also, you don't want to use try/catch for control flow. Consider this (bad code):
try {
FileStream fs = File.Open("somefile.txt", FileMode.Open);
} catch (Exception ex) {
MessageBox.Show("The file does not exist. Please select another file");
}
You'll get more performance from some thing like File.Exists. such as:
if(!File.Exists("somefile.txt"))
MessageBox.Show("The file does not exist.")
EDIT:
found the MSDN direct quote:
Finding and designing away
exception-heavy code can result in a
decent perf win. Bear in mind that
this has nothing to do with try/catch
blocks: you only incur the cost when
the actual exception is thrown. You
can use as many try/catch blocks as
you want. Using exceptions
gratuitously is where you lose
performance. For example, you should
stay away from things like using
exceptions for control flow.

This is a big topic. Start here for some excellent discussion of Exception handling best practices and be prepared for a religious war...
Code Analysis Team Blog
Martin Fowler - Fail Fast
MSDN on Exception Handling
Checked vs Unchecked Exceptions
My own opinion is that for the most part you use "try/finally" a lot, but "catch" very little. The problem is that if you attempt to catch and handle Exceptions in the wrong instances, you may inadvertently put your application in a bad state. As a rule, use dev and test to learn where you actually need to handle an exception. Those will be places that you can't check. i.e. you shouldn't really need to handle nullreference or filenotfound because you can proactively check for those. Only exceptions you know may happen, but you can't do anything about. Beyond that, for the sake of your data's state, let it crash.
If you are swallowing exceptions, it generally means you don't understand your program or why you are getting an exception. Catching System.Exception is the poster child of code smells...

Actually, I very rarely use a catch block except for logging purposes. finally is much more common for me. Most times, lock or using do everything I can usefully do (and indeed, that is a finally also).
Eric Lippert has a blog entry on exceptions that may be useful.

The key to this question is the following line:
// recover
To be able to recover, you have to know what and how to recover. And that's assuming it is possible to recover, which quite frequently it isn't.
You should only use the catch part of try/catch/finally to swallow an exception when you know how to handle the exception, when you know how to recover from it, and when you're sure you can do so without leaving the application in an inconsistent or invalid state.
If you can do this for all possible exceptions in all method calls in your application then go right ahead, otherwise you might need to re-think your #1 priority (sometimes failing fast is a better options than trying to keep an application alive when something has gone wrong, and having a much harder to debug crash later on).

Generally IMO it is better to put smaller chunks that are out of your control in a try catch. If you say:
try
{
//anything that could possibly go wrong
//This kind of thing is only good for Logging IMO and could be done in
//Global.asax
}
How could you possibly know what to do in your catch method cause it could be anything...
Its much better to go:
try
{
//divide user imputs
}
catch(DivideByZeroException)
{
// tell user bad inputs ect....
}
catch (Exception e)
{
//If you choose to throw the exception you should
//***********************
throw;
//VS
throw ex; //Throw ex will restart the stack trace
// recover
}
finally
{
//Clean up resources and continue
}
In which finally is always run

There is performance overhead for try blocks, if you do that your entire function will run slower then it otherwise would. catch (Exception e) is also a bad idea, if you catch you want to do something useful with what you caught, and if you catch all exceptions it is impossible to know what you should be doing.

You can do this, although almost in any given environment you're running in, there's a global exception handler where you can catch and handle even unknown errors.
For web apps, there's the Global.asax, for a console program, just wrap your Main() in a try/catch, for services, there's AppDomain.CurrentDomain.UnhandledException, etc.
You should wrap sections where you can predict what the exception might be in more specific blocks, but the global exception handlers should greatly simplify your code and help you out.

You should only catch and stop the exception without rethrowing it if you can meaningfully handle it. Otherwise it is an error and it should propagate up.
I assume that when they say "this app should never crash" there is an implicit requirement that it behaves correctly. Only stoping exceptions that are meaningfully handled satisfies the behaving correctly requirement.
Typically an app will have a single top-level catch block to catch and log unhandled exceptions. These should occur infrequently (and perhaps your requirement can be interpreted to mean these should not happen at all). If you catch and stop exceptions anywhere else in your code, you risk not discovering these problems. If you catch log and stop in lots of other parts of your code, you have a poorly constructed app from the perspective of separation-of-concerns.

I try to avoid try catch blocks generally. I prefer to use blocks to force the user into obeying the rules of an application. For example, if a user should only enter an int that is equal to or less than an int x I'd use:
if (input > x)
{
Console.WriteLine("Invalid input. Please enter a number that is equal to or less than x.");
{...}
}
rather than using:
catch (IndexOutOfRangeException)
{
//error message here
}
From my own personal experience I find it easier to write as you can avoid encapsulating code in a try block (guarding code).
Of course, there will always be times where using try catch is unavoidable - I just like to work around it where possible.

Our current application has a similar mandate: Never crash. Always back out gracefully. To do this, you have to make sure that every line of code is either enclosed in a try-catch block or only called by code that its exceptions can bubble up into.
Also, to protect against uncaught exceptions, we attach an UnhandledExceptionEventHandler to AppDomain.CurrentDomain.

You should use them anytime a piece of code can thrown an exception.
You have to be careful, catching general exceptions is never a good idea. You have to decide which layer you want to handle them.
Meaning the deeper you are you want to catch very specific excpetion and go more general. In a database catch the SqlException. As you go higher in the stack you catch more exceptions to finally catching the general exception at the very top.
That way you can deal with each exception on a case by case basis. A general exception you aren't going to know what to do with.

public void functionName
{
try
{
//your codes
//sometimes 'return' shows exceptions
}
catch(Exception e)
{
messagebox.show(e.Tostring()); //to know what is the exception
}
finally
{
}
}

try catch in c#:
try{
}
catch (NullReferenceException en)
{
}