Question

What is the correct way to initiate a class in a class? should I put StreamWriter in a method? or this is fine?

class Class1
{
   public static string config = "file.config";
   StreamWriter writer = new StreamWriter(config); 
   public void print (string log) 
   {
     writer.WriteLine(log);
   } 
   public void log_close() 
   { 
      writer.Close();
   }
}

Answer 1

Your closing logic is not thread-safe and does not follow recommendations.

You should use the Disposable pattern because FileStream implements IDisposable.

class Class1 : IDisposable
{ 
   public string config = "file.config";
   StreamWriter writer = new StreamWriter(config); 
   public void print (string log) 
   {
     writer.WriteLine(log);
   } 

   public void log_close() 
   { 
      Dispose();
   }

   public void Dispose() 
   { 
      if (writer != null)
         writer.Close();

      writer = null;
   }
}

And now your Class1 instances can be use with the using statement:

using (var c = new Class1())
{
    c.print("That's all");
}

No need to call Dispose() or close().