Exception handling

[Allie]

Hi, all.

I've never been any good at handling exceptions... So I need your
help.

Within a try{ } block, I have to call a function that has to throw its
own exception. How should I go about doing this?

try {
checkNullHeader( sHeader, ref status );
// ...
}

// ...

// definition of checkNullHeader
void checkNullHeader( AuthHeader sHeader, ref status status )
{
// if token is null or empty, do not even try to authenticate
if( sHeader == null || sHeader.Token == null ||
sHeader.Token.Equals( "" ) )
{
try {
status.Code = Status.StatusCode.UNAUTHORIZED;
status.Description = "Unauthorized";
throw new Exception( "Unauthorized" );
}
catch( Exception e )
{
Console.WriteLine( "Exception caught here:" + e.ToString ( ) );
}
}
}

Is something like this legal? Am I even throwing the exception
correctly? (Seriously. Exceptions are very foreign to me.) Help me!

Thanks.
Allie

 

[Tom Porterfield]

Hi, all.

I've never been any good at handling exceptions... So I need your
help.

Within a try{ } block, I have to call a function that has to throw its
own exception. How should I go about doing this?

try {
checkNullHeader( sHeader, ref status );
// ...
}

// ...

// definition of checkNullHeader
void checkNullHeader( AuthHeader sHeader, ref status status )
{
// if token is null or empty, do not even try to authenticate
if( sHeader == null || sHeader.Token == null ||
sHeader.Token.Equals( "" ) )
{
try {
status.Code = Status.StatusCode.UNAUTHORIZED;
status.Description = "Unauthorized";
throw new Exception( "Unauthorized" );
}
catch( Exception e )
{
Console.WriteLine( "Exception caught here:" + e.ToString ( ) );
}
}
}

Is something like this legal? Am I even throwing the exception
correctly? (Seriously. Exceptions are very foreign to me.) Help me!

Since you are catching the exception thrown within checkNullHeader in
that same function, your outside call will not see the "Unauthorized"
exception. If you simply want to log the "Unauthorized" condition
(you're already setting a status code and description so the caller to
checkNullHeader can inspect those to determine the action to take, the
throwing/catching of an exception with checkNullHeader is a waste.

Can you better define your design?

 

[Allie]

Since you are catching the exception thrown within checkNullHeader in
that same function, your outside call will not see the "Unauthorized"
exception. If you simply want to log the "Unauthorized" condition
(you're already setting a status code and description so the caller to
checkNullHeader can inspect those to determine the action to take, the
throwing/catching of an exception with checkNullHeader is a waste.

Can you better define your design?

So if this function (checkNullHeader) is defined within the try{ }
block of a particular class, it does not need to throw/catch an
exception? (Is it OK to leave throw new Exception( "Unauthorized" );
in the function?)

What if I want to access checkNullHeader from other classes... and/or
not necessarily from within a try{ } block? Will a try-catch block
within checkNullHeader make sense then?

An exception needs to be thrown because, while the code and
description of the status are changing, the calling function is not
using this data to determine a course of action. If the user is not
authorized, the rest of the function should not execute. At least,
that's how I understand it. (I did not write the code. My job is to
take

if( sHeader == null || sHeader.Token == null ||
sHeader.Token.Equals( "" ) ) {
....
}

and turn it into a function, as it is used in a lot of other
functions.)

Thanks,
Allie

 

[Tom Porterfield]

So if this function (checkNullHeader) is defined within the try{ }
block of a particular class, it does not need to throw/catch an
exception? (Is it OK to leave throw new Exception( "Unauthorized" );
in the function?)

What if I want to access checkNullHeader from other classes... and/or
not necessarily from within a try{ } block? Will a try-catch block
within checkNullHeader make sense then?

An exception needs to be thrown because, while the code and
description of the status are changing, the calling function is not
using this data to determine a course of action. If the user is not
authorized, the rest of the function should not execute. At least,
that's how I understand it. (I did not write the code. My job is to
take

if( sHeader == null || sHeader.Token == null ||
sHeader.Token.Equals( "" ) ) {
...
}

and turn it into a function, as it is used in a lot of other
functions.)

A good general rule of thumb is that if you can handle the situation
through logic then you shouldn't throw an exception. So I would code up
a function called isHeaderNull that returns a true if the header is
null, otherwise false. Then the caller of the function need only check
a simple bool value and act accordingly.