I need advice on how to have my C# console application display text to the user through the standard output while still being able access it later on. The actual feature I would like to implement is to dump the entire output buffer to a text file at the end of program execution.
The workaround I use while I don't find a cleaner approach is to subclass TextWriter overriding the writing methods so they would both write to a file and call the original stdout writer. Something like this:
public class DirtyWorkaround {
private class DirtyWriter : TextWriter {
private TextWriter stdoutWriter;
private StreamWriter fileWriter;
public DirtyWriter(string path, TextWriter stdoutWriter) {
this.stdoutWriter = stdoutWriter;
this.fileWriter = new StreamWriter(path);
}
override public void Write(string s) {
stdoutWriter.Write(s);
fileWriter.Write(s);
fileWriter.Flush();
}
// Same as above for WriteLine() and WriteLine(string),
// plus whatever methods I need to override to inherit
// from TextWriter (Encoding.Get I guess).
}
public static void Main(string[] args) {
using (DirtyWriter dw = new DirtyWriter("path", Console.Out)) {
Console.SetOut(dw);
// Teh codez
}
}
}
See that it writes to and flushes the file all the time. I'd love to do it only at the end of the execution, but I couldn't find any way to access to the output buffer.
Also, excuse inaccuracies with the above code (had to write it ad hoc, sorry ;).
The perfect solution for this is to use log4net with a console appender and a file appender. There are many other appenders available as well. It also allows you to turn the different appenders off and on at runtime.
I don't think there's anything wrong with your approach.
If you wanted reusable code, consider implementing a class called MultiWriter or somesuch that takes as input two (or N?) TextWriter streams and distributes all writs, flushes, etc. to those streams. Then you can do this file/console thing, but just as easily you can split any output stream. Useful!
Probably not what you want, but just in case... Apparently, PowerShell implements a version of the venerable tee command. Which is pretty much intended for exactly this purpose. So... smoke 'em if you got 'em.
I would say mimic the diagnostics that .NET itself uses (Trace and Debug).
Create a "output" class that can have different classes that adhere to a text output interface. You report to the output class, it automatically sends the output given to the classes you have added (ConsoleOutput, TextFileOutput, WhateverOutput).. And so on.. This also leaves you open to add other "output" types (such as xml/xslt to get a nicely formatted report?).
Check out the Trace Listeners Collection to see what I mean.
Consider refactoring your application to separate the user-interaction portions from the business logic. In my experience, such a separation is quite beneficial to the structure of your program.
For the particular problem you're trying to solve here, it becomes straightforward for the user-interaction part to change its behavior from Console.WriteLine to file I/O.
I'm working on implementing a similar feature to capture output sent to the Console and save it to a log while still passing the output in real time to the normal Console so it doesn't break the application (eg. if it's a console application!).
If you're still trying to do this in your own code by saving the console output (as opposed to using a logging system to save just the information you really care about), I think you can avoid the flush after each write, as long as you also override Flush() and make sure it flushes the original stdoutWriter you saved as well as your fileWriter. You want to do this in case the application is trying to flush a partial line to the console for immediate display (such as an input prompt, a progress indicator, etc), to override the normal line-buffering.
If that approach has problems with your console output being buffered too long, you might need to make sure that WriteLine() flushes stdoutWriter (but probably doesn't need to flush fileWriter except when your Flush() override is called). But I would think that the original Console.Out (actually going to the console) would automatically flush its buffer upon a newline, so you shouldn't have to force it.
You might also want to override Close() to (flush and) close your fileWriter (and probably stdoutWriter as well), but I'm not sure if that's really needed or if a Close() in the base TextWriter would issue a Flush() (which you would already override) and you might rely on application exit to close your file. You should probably test that it gets flushed on exit, to be sure. And be aware that an abnormal exit (crash) likely won't flush buffered output. If that's an issue, flushing fileWriter on newline may be desirable, but that's another tricky can of worms to work out.
Related
Ok, so let me take a simple example of what I'm trying to describe. This is probably a very "n00b" question, and yet I've ready plenty of programming books and they never have examples like this.
Let's say I have a program like
public class Program
{
private static List<string> _input = new List<string>();
public static void Main()
{
string line;
while((line = Console.ReadLine()) != null)
{
Program._input.Add(line);
}
return 0;
}
}
except want to modify it so that the next time I launch, the lines I added to input the previous time I ran the program are still there. Is there a way to do this (without writing the list to a text file or something like that)? If so, how?
Once your application is closed, everything stored in variables is lost when your application is destroyed.
The only way to persist data is to store it somewhere outside of your program. The most common are files or databases. In your case, you're just storing lines of text so I'd probably go with a file.
You can easily write to the file when the application is closing and then read from the file when the application starts.
If you want save all value of your class you can use a Serialization
you can have some example here : Examples of XML Serialization
But in all case you need to write in a file you can keep it in RAM.
Whenever you close your program, Windows frees memory. Only files are preserved.
Writing file is not evil but just one simple statement.
File.WriteAllLines("lines.txt", _input);
Reading file is also easy.
_input.AddRange(File.ReadAllLines("lines.txt"));
When application is closed on operating system, it is taken out from the computer memory...so you have to save its state to some kind of file or storage devices... as far as I concern that is the only way
I know it sounds really stupid, but I have a really easy application that saves some data from some users on a database, and then I want to write all the data on a .txt file.
The code is as follows:
List<MIEMBRO> listaMiembros = bd.MIEMBRO.ToList<MIEMBRO>();
fic.WriteLine("PARTICIPACIONES GRATUITAS MIEMBROS: ");
mi = new Miembro();
foreach (MIEMBRO_GRATIS m in listaMiembroGratis)
{
mi.setNomMiembro(m.nomMiembro);
mi.setNumRifa(m.numRifa.ToString());
fic.WriteLine(mi.ToString());
}
fic.WriteLine();
As you see, really easy code. The thing is: I show the information on a datagrid and I know there are lots of more members, but it stops writing in some point.
Is there any number of lines or characters to write on the streamwriter?? Why I can't write all the members, only part of them???
fic is probably not being flushed by the time you are looking at the output file; if you instantiate it as the argument for a using block, it will be flushed, closed, and disposed of when you are done.
Also, in case you are flushing properly (but it is not being flushed by the time you are checking the file), you could flush at the end of each iteration:
foreach (MIEMBRO_GRATIS m in listaMiembroGratis)
{
mi.setNomMiembro(m.nomMiembro);
mi.setNumRifa(m.numRifa.ToString());
fic.WriteLine(mi.ToString());
fic.Flush();
}
This will decrease performance slightly, but it will at least give you an opportunity to see which record is failing to write (if, indeed, an exception is being thrown).
Is there any number of lines or characters to write on the
streamwriter??
No, there isn't.
As you see, really easy code. The thing is: I show the information on
a datagrid and I know there are lots of more members, but it stops
writing in some point
My guess is that your code is throwing an exception and you aren't catching it. I would look at the implementation of setNomMiembro, setNumRifa and ToString in Miembro; which, by the way, in the case of setNomMiembro and setNumRifa should probably be implemented as properties ({get;set;}) and not as methods.
For example, calling ToString in numRifa would throw a null pointer exception if numRifa is null.
I'm writing an app (C#) and at times I will need to log to the Windows event log. So the first thing that comes to mind is to write a function in my one and only class and call it when I need it. Something like this:
private void Write_Event_Log(string log, string source, string message, EventLogEntryType type, int eventid)
{
if (!EventLog.SourceExists(source))
EventLog.CreateEventSource(source, log);
EventLog.WriteEntry(source, message, type, eventid);
}
A colleague of mine asked, "why didn't you just create a new class for your event log writer?" So my question is, why would I? And what would this class even look like? And why would I need it when my function works nicely? ok that's 3 questions but you get the point :)
why would I?
To encapsulate the logging functionality into its own class. Why? Single Responsibility Principle http://en.wikipedia.org/wiki/Single_responsibility_principle. Ny mixing it into your class you are making that class be responsible for at least two (2) things: whatever it does and logging.
And what would this class even look like?
public class LogWriter
{
public static Log(string log, string source, string message, EventLogEntryType type, int eventid)
{
if (!EventLog.SourceExists(source))
EventLog.CreateEventSource(source, log);
EventLog.WriteEntry(source, message, type, eventid);
}
}
And why would I need it when my function works nicely?
Think about when you are no longer responsible for the code. Think ahead to when the code grows. Eventually, in addition to logging it might have a host of other very helpful functions included in it. The next programmer would be much happier not having to refactor your work because the design precedent has been set.
This is a very general question about OO design. Your colleague is referring to separation of responsibilities; he doesn't think that the idea of an event log writer fits into the abstraction of the class you put it in, and it deserves its own.
If this is all you are ever going to use it for (this one method) and this program is simple enough that you are implementing it one class, there is no need to use another class to interact with your event writer. If you can conceive that your event writer might be used in a different way, or by a different class, in the future, then yes, absolutely make it is own class so that you avoid future problems where you have to change the source code that uses it.
The function you've written is a small function that doesn't keep state, so another class is not really necessary unless it's to avoid future problems.
Simple, what if you wish to use this method every where in all other parts of your code base? You again copy - paste. Instead have a helper or a Add in class, where just instantiate and keep calling.
Plus if its in a class, you can have more properties and provide more customization methods as well in logging data.
See if you can make use of built in eventlog/trace stuffs.
If it's a small application (which with one class it must be) then it probably doesn't matter.
But design wise in a larger application, you probably would want to consider having the logging functionality in a class by itself in order to keep each class as narrowly focused as possible.
For the same reason that someone put SourceExists(Source) and CreateEventSource(source, log) into their own class, so you could call them just by referencing the assembly that has that class defined, and writing
EventLog.SourceExists(source);
or
EventLog.CreateEventSource(source, log);
So if you will never ever need to write to the event log in any other application you ever write, then what you are doing is fine... but if you might ever need this again, then .....
I think you should have seperate class because if you are going to create more no.of classes in your application you can use same logging for all of them see below example
public static class Logger
{
private static string logFilePath = string.Empty;
public static void Log(string logMessage, TextWriter w)
{
w.Write( logMessage);
w.Flush();
}
public static void Log(string textLog)
{
string directoryString =
filepath+ #"\Logging";
Directory.CreateDirectory(directoryString);
logFilePath = directoryString + "\\" +
DateTime.Now.ToShortDateString().Replace("/", "") + ".txt";
StreamWriter sw = null;
if (!File.Exists(logFilePath))
{
try
{
sw = File.CreateText(logFilePath);
}
finally
{
if (sw != null) sw.Dispose();
}
}
using (StreamWriter w = File.AppendText(logFilePath))
{
Log(textLog, w);
w.Close();
}
}
I agree that you shouldn't create a new class for writing directly to the event log, but for another reason. That class already exists!
Consider using the built-in debug/tracing mechanisms in System.Diagnostics:
Debug output
Trace output
These are standard classes that dump information to a collection of TraceListener objects, of which many useful types already exist:
DefaultTraceListener - Dumps output to standard debug out, I believe via OutputDebugString().
EventLogTraceListener - Dumps output to the windows event log.
So this changes your output mechanism from a programmatic question into a configuration question. (Yes, if you're working in a straight-up managed app, you can populate your TraceListener collection via your app.config.) That means that everywhere you simply use the appropriate Trace.Write() or Debug.Write() call (Depending on if your want the output in a release build), and the configuration determines where the output goes.
Of course, you can also populate your TraceListener collection programmatically, it's fun and simple.
And this way you don't have to build up your own home-grown logging infrastructure. It's all built-in! Use it in good health! :D
If, on the other hand, you insist on rolling your own (a bad idea, I think), your colleague is right. It's a separate responsibility and belongs in a separate class. I would expect static methods for output because there's probably no concept instances of your debug log. In fact, I'd expect an interface very similar to System.Diagnostics.Debug, so yeah, just use that one instead.
Depending on your approach, you may run into a subtle gotcha' that's in the docs, but not immediately obvious without a careful reading. I found an answer for it elsewhere.
I'm writing a little application whereby I want to write the results of the operations to a file.
Basically what I want to do is open a stream to a file (I'm thinking FileStream, but am open to suggestions), write data to the file, then close it at a later date.
So I've got a class called ReportFile, with methods:
.Create( string path )
.WriteInfo( string a, string b, string c ) ; //Or something like this...
//Then sometime in the future
.Close()
So the class using the ReportFile class will create an instance, call WriteInfo(..) multiple times until it is finished doing whatever it needs to do, then call Close() at some point in the future.
Now I know I need to implement a Dispose pattern on the ReportFile class to ensure that if anything goes screwey that the handle to the file gets appropriately dealt with.
However I haven't been able to find anything thus far on the interweb showing a good way of keeping the file open and then checking to see if it needs to be closed, most of the examples just open the file do the writing, then close it - all within a using{} construct.
In the ReportFile class I want to be able to check if the FileStream instance is not closed so that I can close it and free up resource.
Anyone know of a good link to reference or any other advice ?
(Ohh I should mention that I don't do C# full time, it's only a hobby thing, so if this is a dumb question, my apologies ;-)
Is there a particular reason that you have to keep the file open?
In this situation I would simply open the file each time using FileMode.Append (or pass append=true to StreamWriter ctor) and then close it again afterwards with a using. eg:
void WriteInfo(string text)
{
// Second parameter to StreamWriter ctor is append = true
using(StreamWriter sw = new StreamWriter(logFilePath, true))
{
sw.WriteLine(text);
}
}
Taking this approach you can don't really need a Create() or Close() method. The append=true will create the file if it does not exist.
The ReportFile would just have a TextWriter instance variable - which you would dispose within your own Dispose() method.
Why do you want to have an explicit Close() method, btw? Your callers should be using a using statement anyway, so why would they want to explicitly call Close as well?
Justa, i think that you're overthinking this feature a bit. The reason that you're seeing examples with the using construct is that using{} with file write is quite fast and safe.
Chances are that you're not opening and closing the file several times a second so there's no need to keep it open all the time and thus risking leaving the app without closing the file (which is a PITA to fix after the fact.) Using the using construct makes certain that the resource, your file in this case, is released and closed properly.
Another piece of advice for programming: don't worry about efficiency at the outset. Get it working first the simplest way you can and improve speed/performance later only if it's necessary.
public void Create(string path) {
mStream = new FileStream(path);
}
public void Dispose() {
if (mStream != null)
mStream.Dispose();
}
I would suggest using the "using" construct and keep the file open only whilst saving.
An idea might be to build the content in memory then save it when you're ready. using a StringBuilder for example.
In the case you simply won't use a using {} construct, you can use the IDisposable interface: http://msdn.microsoft.com/en-us/library/system.idisposable.dispose.aspx
I'm using TextWriterTraceListener to log diagnostics messages to a text file. However I wan't also to log a timestamp of every trace message added. Is it possible to define a kind of formatter for the listener that would automatically add timestamps?
Currently I'm adding timestamps manually on every Trace.WriteLine() call but this isn't very comfortable.
I suggest you use Log4Net instead, which has a lot more customizability.
Alternatively you could write your own TraceListener implementation which put the timestamps on for you. You may even be able just derive from TextWriterTraceListener and override Write and WriteLine:
public override void Write(string x)
{
// Use whatever format you want here...
base.Write(string.Format("{0:r}: {1}", DateTime.UtcNow, x));
}
public override void WriteLine(string x)
{
// Use whatever format you want here...
base.WriteLine(string.Format("{0:r}: {1}", DateTime.UtcNow, x));
}
As noted in comments, this ends up with date duplication for TraceInformation, because that calls Write twice. Using a "proper" logging framework is definitely better.
I recently encountered similar situation and it looks like now we have a tool very much fit for the task, namely Essential Diagnostics. You set up a listener in app.config like in code below and then just place Essential.Diagnostics.dll into the same folder. NO RECOMPILING IS REQUIRED. You can use this with any applications that uses System.Diagnostics for tracing, even if you do not own the source. Isn't that marvelous?
<sharedListeners>
<add name="rollingfile"
type="Essential.Diagnostics.RollingFileTraceListener, Essential.Diagnostics"
initializeData="{ApplicationName}-{DateTime:yyyy-MM-dd}.log"
convertWriteToEvent="true"
template="{DateTime:yyyy-MM-dd HH:mm:ss.fff} {Message}{Data}"
/>
</sharedListeners>
You could write your own TextWriterTraceListener subclass which overrides the WriteLine methods, decorates the line, and then passes the decorated string to the base class implementation to do the actual output.
Or just add "DateTime" as a traceOutputOption.
Not really an answer to your question but have you considered just using log4Net?
You can configure it to add times etc, along with a vast amount of other useful functionality.
Consider using The Logging Application Block
Even though this is old and an answer has been accepted, I will throw in one more option. You can use the Ukadc.Diagnostics addon from codeplex. Among other things, it enables you to define custom formatting, similar to the formatting that you can define with log4net and NLog. It is a configuration-only dependency. That is, you configure the use of Ukadc.Diagnostics through the app.config file. There are no source dependencies (you continue to log via System.Diagnostics not through a special api). Having said that, there are some limitations that you should be aware of:
The formatting options currently implemented in Ukadc.Diagnostics really only work correctly when logging with TraceSources. When logging with Trace.Write and Trace.WriteLine the TraceEventCache object is not filled in and that is where most of the formatting objects get their information.
You must use a Ukadc.Diagnostics TraceListener (or a custom listener derived from the Ukadc.Diagnostics base TraceListener) to get the custom formatting to appear in your output. If you found a new super duper rolling file TraceListener, you will have to do some work to use it in conjunction with the Ukadc.Diagnostics formatting. This might be as difficult as reimplementing the listener in terms of the Ukadc.Diagnostics base TraceListener. Or it could be easier, if you could just create a new Ukadc.Diagnostics-based TraceListener that contains the super duper rolling TraceListener, formats the messages per Ukadc.Diagnostics, and then delegates to the contained listener's Write/WriteLine methods.