How to find path of active app.config file?

I'm trying to finish this exception handler:

if (ConfigurationManager.ConnectionStrings["ConnectionString"]==null)
{
    string pathOfActiveConfigFile = ...?
    throw new ConfigurationErrorsException(
       "You either forgot to set the connection string, or " +
       "you're using a unit test framework that looks for  "+
       "the config file in strange places, update this file : " 
       + pathOfActiveConfigFile);
}

This problem seems to only happen to me when I'm using nUnit.

Solution 1:

Try this

AppDomain.CurrentDomain.SetupInformation.ConfigurationFile

Solution 2:

Strictly speaking, there is no single configuration file. Excluding ASP.NET¹ there can be three configuration files using the inbuilt (System.Configuration) support. In addition to the machine config: app.exe.config, user roaming, and user local.

To get the "global" configuration (exe.config):

ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
                    .FilePath

Use different ConfigurationUserLevel values for per-use roaming and non-roaming configuration files.

¹ Which has a completely different model where the content of a child folders (IIS-virtual or file system) web.config can (depending on the setting) add to or override the parent's web.config.