CODEWITHSUNDEEP
file-ioc#-2.0disposeidisposableusing
char m
char m

Reputation: 8336

C#: are both using and try-finally-Dispose bad options with StreamReader?

think about this:

StreamReader reader = null;

try
{
    reader = new StreamReader(_fileName);
}
catch
{
    //show error that file not found
    reader.Dispose();
    return false;
}

try
{
    //code to read file
}
catch
{
   //show error badly formed file
}
finally
{
    reader.Dispose();
}
//return

the code above does not work when file can't be opened because it calls Dispose for null which results in exception.

i don't want to use using because i want to separate problems with opening the file and reading it. This could be achieved with million different catches but i don't want to go that way. Plus if using is same as try-finally would "hidden Dispose" throw an unwanted exception anyway? which would be the best way when all i need is to catch an exception opening it and an exception reading it?

Thanks & BR - Matti

Upvotes: 0

Views: 1129

Answers (4)

stuartsmithuk
stuartsmithuk

Reputation: 31

The StreamReader can throw the following exceptions so you could just handle these accordingly:-

ArgumentException
ArgumentNullException
FileNotFoundException
DirectoryNotFoundException
NotSupportedException
ArgumentOutOfRangeException

Upvotes: 1

Oded
Oded

Reputation: 499132

It is better to use the using statement:

using(StreamReader reader = new StreamReader(_fileName))
{
}

The compiler will create the correct dispose semantics for you.

And you can still use try with this, not worrying about disposing it yourself:

try
{
    using(StreamReader reader = new StreamReader(_fileName))
    {
         try
         {
            //code to read the file
         }
         catch
         {
            //show error badly formed file
         }
    }
}
catch
{
    // show error that file not found
}

Upvotes: 6

Marnix van Valen
Marnix van Valen

Reputation: 13673

You should check whether the reader is null before you dispose it. Like so:

StreamReader reader = null;
try
{
    //code to read file
}
catch
{
   //show error badly formed file
}
finally
{
  if( null != reader )
  {
    reader.Dispose();
  }
}

Upvotes: 2

Liviu Mandras
Liviu Mandras

Reputation: 6627

Your code is correct if you check reader for null before calling any methods on it, whereever that reader is located.

Using statement is not mandatory but is desirable.

Upvotes: 2

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