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Using app.config correctly

In several C# projects I have been using an app.config file to pass various settings to my program, settings like connectionstrings, power levels etc.
However sometimes I have come in situations where the settings aren't updated as expected and I have concluded that I am not that well informed with the proper use of app.config file.
Example:
Replacing the .exe file with a new version (where settings are different) to the output directory without changing the exe.config, results in the program seeing the hard-coded settings and not the settings of the existing .exe.config
So my Questions are:
What is the exact role of exe.manifest file
Every time I create a new .exe do I have to paste in the output folder anything else except the .exe file?
Whats the difference in obtaining the setting value by: ConfigurationManager.'settingName'... rather than:
Properties.Settings.Default.'settingName'?
What is the role of app.config build action?
Sorry If I am asking too much in a single Question.

The app.config file is a file that gets a special treatment when running the associated application. If you executable is named MyApp.exe the app.config file should be named MyApp.exe.config. The role of the app.config build task is to copy the file named app.config in your project to MyApp.exe.config in the output directory.
.NET provides ways to read the contents of the file (it is in XML format) and various parts of .NET will look for different sections in this XML to provide configuration.
A widely used section is the settings section you refer to as Properties.Settings.Default. This section plays together with Visual Studio that provides an editor for application settings. The settings are accessed in the code by using a generated class. Adding a setting will add a property to this class and this property is initialized from a value in the app.config file.
In the Visual Studio editor you can set a value for the setting and you can think of this as a default value for the setting. However, if you overwrite the value in the app.config file the later will take precedence. This allows you to modify the app.config file after installation and rerun the application with a modified setting.
You can also access application settings the app.config file using other methods, but in my oppinion using the Visual Studio editor and the code generated class is the best way to do that.
I am not sure I fully understand the problem that you experience. If you update MyApp.exe and leave MyApp.exe.config intact you should not see a change in the settings used by the application (unless of course you have renamed or changed some settings).
The manifest file provides information about side-by-side assemblies and can be used to request elevated privileges among other things. This is not related to the app.config file.

There quite a few resources about that.
See http://msdn.microsoft.com/en-us/library/ms229689%28v=vs.90%29.aspx
and the (better) overview: http://msdn.microsoft.com/en-us/library/k4s6c3a0%28v=vs.110%29.aspx
app.config is a very powerful tool. It addresses many issue like versioning, migration, upgrading etc. but this requires some in-depth reading from the links above.

Maybe one thing you could do, if you want to copy only .exe file every time you build your app, is make a settings.ini or settings.txt file, put your parameters in this file (that are not secret of course) and read all your settings from there when you start your app.
You can put all your connection string logic in your login form if you have one...

Where the Devil is my Applications .config file?

All, I have a large application. This application uses a .config file to deal with its various settings. This is fine in development, and the .config file is found and working happily in the respective \bin folders (Release and Debug). I have written a NSIS installer an I am now running the app; it is working perfectly, saving settings, restoring settings and generally being a good LAD.
However, the 'MyApp.exe.config' is not where the settings are being written (I have checked and even deleted this so it could be recreated). It is also not in ...Users\Me\AppData\Roaming\MyApp?
Where the Devil is my applications config file?
Thanks again for your time.
Edit. I have printed out System.Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) and this points to the Roaming AppData directory above.

The configuration system for .net gets its settings from several locations.
General config comes from:
The first location is the machine.config file that ships with the .net framework.
The next location is the application's configuration file.
Next the settings API gets values from (using the default provider):
Hard-coded defaults when the app was compiled.
The application configuration file.
The user's settings file.
If the application's configuration file does not exist it will not be automatically created (doing so would be pointless since it would only contain the defaults the application already knows).
Saving the settings will however create a new user settings file as normal.

Where to save project related text files?

For testing and debugging purposes, I just hard-coded the file paths for the text files that would be used by my application, e.g.
const string CONFIG_FILE_PATH = #"C:\myconfigfile.txt";
But I don't think it's a good idea to leave it as it is in the Beta/Release version.
So I am wondering, what would be the best location for saving these configuration files that will be used / read by the application? Any suggestions?
Many Thanks.

Why not save the strings in the Settings section of your project? GRight click on your project in Solution Explorer, select Properties, go to the Settings section and add a new string with your file path. Then, in your code, you can access it like this:
using ProjectName.Properties;
var path = Settings.Default.MySetting;
To change the setting:
Settings.Default.MySetting = newPath;
Settings.Default.Save();

In the same folder as the executable.
But you should consider using a Settings class (you can read more here). Visual Studio can automatically create a strongly typed wrapper around a section in the app.config file.
The settings are stored in the same file as the executable, but can be overridden (and saved from the application) in a matching file in the user profile for each user.

Another option: If the test config file is intended to sit along side your executable, you can "Add" "Existing Item..." to your project and then change its properties to "Copy always" or "Copy if newer". During debugging, the executable should be able to find the copy of the config in its current working directory.
This isn't such a useful solution when there's a lot of testing to do.

For settings I would certainly use the app.config file. This is proposed by Microsoft and apart from that it is pretty much the easiest way to handle application settings anyway.
For other files I'd recommend either the applications local or roaming settings path, depending on weather you only need the data local or not. For compact, local databases I tend to use this approach. The application directory, as suggested by Albin, is a bad idea. You cannot be sure that the user is actually allowed to write to that directory and/or files in that directory (i.e. the app was pre-installed by an admin with elevated rights).
To get the location of the local paths use
ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoamingAndLocal)
and for the roaming path
ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.PerUserRoaming)
More information on Windows User Profiles (the actual paths in different versions of Windows for example, you can find here: http://msdn.microsoft.com/en-us/library/aa372123.aspx

Store user settings into application folder

I'm using setting from my C# application like this:
String str = Properties.Settings.Default.SETTINGS_NAME;
When I save this settings, a settings file is created on
C:\Documents and Settings\<user name>\Local Settings\Application Data\<comp name>\Keb.exe_Url_pbs4eg1o2ija22omldrwjxhdam0jxxi5\1.0.0.0\user.config
Is there a way to change this path to Application.ExecutablePath\user.config, and use it next time so my application can be more portable ?

You can control the location of the user.config file by creating a custom SettingsProvider. Luckily for you, someone at CodeProject already did that.
See my answer here for all the details: How to make designer generated .Net application settings portable

If you want it to be Single user or in other way make the configuration of your application portable i will use a custom config file like an .ini file and keep it my app's root folder.
That way any one want to have those settings can just copy it in his own app's root folder on some other computer. When app runs it just loads the settings and behave accordingly.
save data in a fixed format like
[setting_name] = [Setting_value]\n
or in XML file, with Tag name for setting and value for... well... value :)
You can also go with registry setttings but user don't feel it trivial to copy and merge .reg files
This is the way i have seen some PC Games (for eg. i frequently changed Crysis and MassEffect settings) and Softwares save their config files.

C# Settings xml file location

I have a project that reads in a file based on a value in a C# Setting class. This value however changes from machine to machine and Id rather not ask the user the first time the program is run as its a corporate environment, instead Id like it to be set in the installer, but where is the file located? Is there an easier method?
This is a visual studio addin not a standalone program

From your post it appears you have a windows application? , you can store an initial value in the application config, you can make an installer in Visual Studio and write custom actions that can write values to the file on first install in you install project.

The configure file is the easiest way to do what you are asking, however it is NOT the best. In fact it is recommended Not to use .config files for such cases.
whenever users install an 'update', there is a risk of overwriting their existing changes.
some businesses might have policy restrictions on the .config files.
the user cannot easily move his settings from one PC to another.
From my own experience, using XML, MS-Access, Registry or text files to store user settings has proven more useful than using the .config files.

I believe you are talking about designer-generated settings (the .settings file)?
The exact path usually contains some sort of a Hash (check this link). I usually have my own settings class which I serialize to and from xml using XmlSerializer, which gives me more freedom (I think C# settings files don't allow you to add custom enums, for example, or they make it a bit harder to do it than simply adding them to the .settings file).
However, maybe there is no need to set values during installation? For example, you could add a FirstStartup setting (set to true initially), which you can read when your App is started for the first time, and then set it to false. That way you can set your default settings when you detect a "first startup".

You will certainly need some sort of custom action at the end of your installer. You haven't mentioned what technology you're using to deploy your application so I will refrain from giving any specific guidance.
I recommend setting the value in your App.config. This is an xml file which will be named MyApplication.exe.config in the same directory as your application. Add it to your installer if it is not there already. In your installer, add a new setting:
<configuration>
<appSettings>
<add key="MySetting" value="My Value"/>
</appSettings>
</configuration>
In your code, retrieve the setting:
String setting = ConfigurationSettings.AppSettings["MySetting"];
If this is a machine-wide setting, this installer is the right place to set this. If you do it on the first execution you will run into a host of problems with permissions on the files and directories if the first person to run the app is a user with limited permissions.

Registry or an INI file or a XML file whatever suits you best.

Best option would be registry. Istalling the application will require Admin access so writing to the registry during installation will not be an issue.
More over if some one accidently deletes the ini or settings file then the program might stop working.

You said that this is for a corporate environment. You can create an administrative template for group policy to set the default in the registry. Then, your program can just query that one registry value if the default hasn't already been set.

I personally would never use web.config or app.config. Just read your own xml file, have a look at my post on this:
http://www.picnet.com.au/blogs/Guido/post/2009/09/10/XML-Settings-Files-No-more-webconfig.aspx
Thanks
Guido

To answer the "Where is the file located" bit of the original question for those interested (I'm assuming that the "settings file" in question is the "Settings File" item available from the "Add New Item" dialogue).
In Win7 (and probably all the other ones) the settings file will generate under the path:
C:\Users\[user]\AppData\Local
The folder structure from here on out depends on your AssemblyInfo and build information, the "AssemblyCompany" field (if populated) is used for the top-most folder, beneath this is a folder copying the application executable name, followed by the build and then finally the settings file (named "*.config").
In my case, the complete path is as follows:
C:\Users\[user]\AppData\Local\[company_name]\Application.exe_StrongName_zx0v1qxyoass4d0z3mtwe3vbrhaehkjg\0.0.5812.21662\user.config

My case is different, my project is a class library (dll) which have the app.config file. I decided to create 4 application settings variables (title, url, limit, rate). To create this, i right-click ont he project --> Properties --> Settings. this values you can retrieve in code using this command --> Settings.Default.title, ...etc
the problem is let say i instantiate 5 objects (same object for example MyProject.MyClass) from this library, i want the instance be able to have its own settings. i mean each of the instance may have their xml setting file. can this be done?