Which method is more efficient (time, memory, resource-releasing, exception scenario) ?
public static string getFileData(string filePath)
{
using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read))
{
using (StreamReader r = new StreamReader(fs))
{
return r.ReadToEnd();
}
}
}
OR
public static string getFileData(string filePath)
{
return (new StreamReader(new FileStream(filePath, FileMode.Open, FileAccess.Read)).ReadToEnd());
}
first without a doubt - you're atleast disposing of the resources you're using. In your second case, maybe if it was being stored into a static variable so only reading once it might be okay, but still not disposing diligently
CLR will generate one code approximately for both code, so two code are same
Related
I'm experimenting with shortening and refining my code as much as possible. One of the ideas I had involves returning a string from a single line of code, employing using to ensure that the accessed file becomes available again when the transaction is complete. My objective is to get as close to a single line of code as possible, however I am having trouble finding a way around the immutability of strings.
The following code is invalid:
string sample()
{
try{ using( string example = (new StreamReader
(new FileStream
("", FileMode.Open, FileAccess.Read),
Encoding.UTF8).ReadToEnd())) }
//I haven't quite worked out returning the value yet, but this is irrelevant here
}
The working code would be as follows:
string sample()
{
FileStream fs = new FileStream("", FileMode.Open, FileAccess.Read);
try{
using(StreamReader rdr = new StreamReader(fs);
return rdr.ReadToEnd();
}
}
I could easily simplify this by doing the following:
string sample()
{
try
{
return (new StreamReader(new FileStream
("", FileMode.Open, FileAccess.Read),
Encoding.UTF8).ReadToEnd());
}
}
However, that may not close the file after the transaction is complete (if that's wrong please let me know). Is there a way to work around the immutability of a string here, or am I looking for the impossible?
It looks like you want a way to create an expression from a using statement. You can create a function:
public static T Use<TRec, T>(TRec resource, Func<TRec, T> f) where TRec : IDisposable
{
using(resource) { return f(resource); }
}
then do
string s = Use(new StreamReader(new FileStream("", FileMode.Open, FileAccess.Read), Encoding.UTF8), sr => sr.ReadToEnd());
The new Visual Studio 2012 is complaining about a common code combination I have always used. I know it seems like overkill but I have done the following in my code 'just to be sure'.
using (var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using (var sr = new StreamReader(fs))
{
// Code here
}
}
Visual studio is 'warning' me that I am disposing of fs more than once. So my question is this, would the proper way to write this be:
using (var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
var sr = new StreamReader(fs);
// do stuff here
}
Or should I do it this way (or some other variant not mentioned).
var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
using (var sr = new StreamReader(fs))
{
// Code here
}
I searched several questions in StackOverflow but did not find something that addressed the best practice for this combination directly.
Thank you!
The following is how Microsoft recommends doing it. It is long and bulky, but safe:
FileStream fs = null;
try
{
fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
using (TextReader tr= new StreamReader(fs))
{
fs = null;
// Code here
}
}
finally
{
if (fs != null)
fs.Dispose();
}
This method will always ensure that everything is disposed that should be despite what exceptions may be thrown. For example, if the StreamReader constructor throws an exception, the FileStream would still be properly disposed.
Visual studio is 'warning' me that I am disposing of fs more than once.
You are, but that is fine. The documentation for IDisposable.Dispose reads:
If an object's Dispose method is called more than once, the object must ignore all calls after the first one. The object must not throw an exception if its Dispose method is called multiple times.
Based on that, the warning is bogus, and my choice would be to leave the code as it is, and suppress the warning.
As Dan's answer only appears to work with StreamWriter, I believe this might be the most acceptable answer.
(Dan's answer will still give the disposed twice warning with StreamReader - as Daniel Hilgarth and exacerbatedexpert mentions, StreamReader disposes the filestream)
using (TextReader tr = new StreamReader(new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))
{
string line;
while ((line = tr.ReadLine()) != null)
{
// Do work here
}
}
This is very similar to Daniel Hilgarth's answer, modified to call dispose via the Using statement on StreamReader as it is now clear StreamReader will call dispose on FileStream (According to all the other posts, documentation referenced)
Update:
I found this post. For what it is worth.
Does disposing streamreader close the stream?
Yes, the correct way would be to use your first alternative:
using (FileStream fs = new FileStream(filePath, FileMode.Open,
FileAccess.Read, FileShare.ReadWrite))
{
TextReader tr = new StreamReader(fs);
// do stuff here
}
The reason is the following:
Disposing the StreamReader only disposes the FileStream so that's actually the only thing you need to dispose.
Your second option (just the inner "using") is no solution as it would leave the FileStream undisposed if there was an exception inside the constructor of the StreamReader.
It's because the way you used StreamReader disposes the stream when it is disposed. So, if you dispose the stream too, it's being disposed twice. Some consider this a flaw in StreamReader--but it's there none-the-less. In VS 2012 (.NET 4.5) there is an option in StreamReader to not dispose of the stream, with a new constructor: http://msdn.microsoft.com/en-us/library/gg712952
Two solutions:
A) You trust Reflector or Documentation and you know *Reader and *Writer will close the underlying *Stream. But warning: it won't work in case of a thrown Exception. So it is not the recommended way:
using (TextReader tr = new StreamReader(new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))
{
// Code here
}
B) You ignore the warning as documentation states The object must not throw an exception if its Dispose method is called multiple times. It's the recommended way, as it's both a good practice to always use using, and safe in case of a thrown Exception:
[SuppressMessage("Microsoft.Usage", "CA2202:Do not dispose objects multiple times")]
internal void myMethod()
{
[...]
using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (TextReader tr = new StreamReader(fs))
{
// Code here
}
}
Given all the nonsense this (perfectly legitimate!) question generated, this would be my preference:
FileStream fs = null;
TextReader tr= null;
try
{
fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
tr= new StreamReader(fs);
// Code here
}
finally
{
if (tr != null)
tr.Dispose();
if (fs != null)
fs.Dispose();
}
The links below illustrate perfectly legal syntax. IMO, this "using" syntax is far preferable to nested "using". But I admit - it does not solve the original question:
http://blogs.msdn.com/b/ericgu/archive/2004/08/05/209267.aspx
.NET - Replacing nested using statements with single using statement
IMHO...
Is there any chance that fileStream object will likely be destroyed before its call to the Close method as below?
FileStream fileStream = new FileStream(xxx);
StreamReader txtReader = new StreamReader(fileStream);
curLog = txtReader.ReadToEnd();
txtReader.Close();
fileStream.Close();
Is there any chance that fileStream object will likely be destroyed
before its call to the Close method as below?
No.
But you should never write code like that. You should always wrap IDisposable resources in using statements to ensure that they will be disposed even if an exception is thrown and that you won't be leaking handles.
using (FileStream fileStream = new FileStream(xxx))
using (StreamReader txtReader = new StreamReader(fileStream))
{
curLog = txtReader.ReadToEnd();
}
But for the purpose of this specific example you could simply use the ReadAllText method.
string curLog = File.ReadAllText(xxx);
No, there isn't any chance that it is closed before that. And i would recommend using it like this
FileStream fileStream = new FileStream(xxx);
using (StreamReader txtReader = new StreamReader(fileStream))
{
curLog = txtReader.ReadToEnd();
}
Should I be using the using keyword or a dispose method with the following code (since I am opening a stream):
class Program
{
static void Main(string[] args)
{
var x = Deserialize<Dog>(new FileStream(#"C:\Documents and Settings\name\Desktop\demo.xml", FileMode.Open));
}
static T Deserialize<T>(Stream s)
{
XmlSerializer ser = new XmlSerializer(typeof(T));
return (T)ser.Deserialize(s);
}
}
If not, can you please explain why not (does a new FileStream automatically dispose/close the stream)?
You should be using using:
using(var stream = new FileStream(#"C:\path\demo.xml", FileMode.Open))
{
var x = Deserialize<Dog>(stream);
// more code ...
}
Yes you should dispose the stream. If you were to use the File.ReadAllText() for example, this static method would open a stream and dispose it for you. I would suggest a Using, this is because it'll handle exceptions too. For example in this noddy example:
This version correctly disposes the FileStream:
using(FileStream fs = FileStream(path, FileMode.Open))
{
throw new Exception();
}
This example leaks the resources used by the FileStream, you could add try/catch blocks but then it's less readable.
FileStream fs = new FileStream(path, FileMode.Open);
throw new Exception();
fs.Dispose();
If you use using block , he execute in the end of treatment Dispose method.
You use using, because FileStream is non managed object, so Garbage collector don't have informatiosn abouts this object in order to clean, so the developper must clean ressource in order to help your GC.
Link : http://msdn.microsoft.com/fr-fr/library/yh598w02(v=vs.80).aspx
you should use Using with everything that implements IDisposable :)
As already mentioned, you should use using. But why? Well, as already mentioned you should use using for all objects that implements IDisposable.
In your case, FileStream inherits from the Stream object which is implementing IDisposable. Read more about FileStream here: msdn
The new Visual Studio 2012 is complaining about a common code combination I have always used. I know it seems like overkill but I have done the following in my code 'just to be sure'.
using (var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
using (var sr = new StreamReader(fs))
{
// Code here
}
}
Visual studio is 'warning' me that I am disposing of fs more than once. So my question is this, would the proper way to write this be:
using (var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
var sr = new StreamReader(fs);
// do stuff here
}
Or should I do it this way (or some other variant not mentioned).
var fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
using (var sr = new StreamReader(fs))
{
// Code here
}
I searched several questions in StackOverflow but did not find something that addressed the best practice for this combination directly.
Thank you!
The following is how Microsoft recommends doing it. It is long and bulky, but safe:
FileStream fs = null;
try
{
fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
using (TextReader tr= new StreamReader(fs))
{
fs = null;
// Code here
}
}
finally
{
if (fs != null)
fs.Dispose();
}
This method will always ensure that everything is disposed that should be despite what exceptions may be thrown. For example, if the StreamReader constructor throws an exception, the FileStream would still be properly disposed.
Visual studio is 'warning' me that I am disposing of fs more than once.
You are, but that is fine. The documentation for IDisposable.Dispose reads:
If an object's Dispose method is called more than once, the object must ignore all calls after the first one. The object must not throw an exception if its Dispose method is called multiple times.
Based on that, the warning is bogus, and my choice would be to leave the code as it is, and suppress the warning.
As Dan's answer only appears to work with StreamWriter, I believe this might be the most acceptable answer.
(Dan's answer will still give the disposed twice warning with StreamReader - as Daniel Hilgarth and exacerbatedexpert mentions, StreamReader disposes the filestream)
using (TextReader tr = new StreamReader(new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))
{
string line;
while ((line = tr.ReadLine()) != null)
{
// Do work here
}
}
This is very similar to Daniel Hilgarth's answer, modified to call dispose via the Using statement on StreamReader as it is now clear StreamReader will call dispose on FileStream (According to all the other posts, documentation referenced)
Update:
I found this post. For what it is worth.
Does disposing streamreader close the stream?
Yes, the correct way would be to use your first alternative:
using (FileStream fs = new FileStream(filePath, FileMode.Open,
FileAccess.Read, FileShare.ReadWrite))
{
TextReader tr = new StreamReader(fs);
// do stuff here
}
The reason is the following:
Disposing the StreamReader only disposes the FileStream so that's actually the only thing you need to dispose.
Your second option (just the inner "using") is no solution as it would leave the FileStream undisposed if there was an exception inside the constructor of the StreamReader.
It's because the way you used StreamReader disposes the stream when it is disposed. So, if you dispose the stream too, it's being disposed twice. Some consider this a flaw in StreamReader--but it's there none-the-less. In VS 2012 (.NET 4.5) there is an option in StreamReader to not dispose of the stream, with a new constructor: http://msdn.microsoft.com/en-us/library/gg712952
Two solutions:
A) You trust Reflector or Documentation and you know *Reader and *Writer will close the underlying *Stream. But warning: it won't work in case of a thrown Exception. So it is not the recommended way:
using (TextReader tr = new StreamReader(new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite)))
{
// Code here
}
B) You ignore the warning as documentation states The object must not throw an exception if its Dispose method is called multiple times. It's the recommended way, as it's both a good practice to always use using, and safe in case of a thrown Exception:
[SuppressMessage("Microsoft.Usage", "CA2202:Do not dispose objects multiple times")]
internal void myMethod()
{
[...]
using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (TextReader tr = new StreamReader(fs))
{
// Code here
}
}
Given all the nonsense this (perfectly legitimate!) question generated, this would be my preference:
FileStream fs = null;
TextReader tr= null;
try
{
fs = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
tr= new StreamReader(fs);
// Code here
}
finally
{
if (tr != null)
tr.Dispose();
if (fs != null)
fs.Dispose();
}
The links below illustrate perfectly legal syntax. IMO, this "using" syntax is far preferable to nested "using". But I admit - it does not solve the original question:
http://blogs.msdn.com/b/ericgu/archive/2004/08/05/209267.aspx
.NET - Replacing nested using statements with single using statement
IMHO...