title: How to write to a file in .NET Core?
body: <p>I want to use the Bluetooth LE functions in .NET Core (specifically, BluetoothLEAdvertisementWatcher) to write a scanner which logs information to a file. This is to run as a desktop application and preferably as a command line app.</p>
  
  <p>Constructors like System.IO.StreamWriter(string) are not available, apparently. How do I create a file and write to it?</p>
  
  <p>I would be just as happy to be able to do a System.Console.WriteLine(string) but that doesn't seem to be available under .NET Core either.</p>
  
  <p>Update: To clarify, if I could have a program that looks like this run without error, I'll be off to the races.</p>
  
  <pre><code>using System;
  using Windows.Devices.Bluetooth.Advertisement;
  
  namespace ConsoleApplication
  {
      public class Program
      {
          public static void Main(string[] args)
          {
              BluetoothLEAdvertisementWatcher watcher = new BluetoothLEAdvertisementWatcher();
              Console.WriteLine("Hello, world!");
          }
      }
  }
  </code></pre>
  
  <p>Update 2: Here's the project.json file:</p>
  
  <pre><code>{
    "dependencies": {
      "Microsoft.NETCore.UniversalWindowsPlatform": "5.0.0"
    },
    "frameworks": {
      "uap10.0": {}
    },
    "runtimes": {
      "win10-arm": {},
      "win10-arm-aot": {},
      "win10-x86": {},
      "win10-x86-aot": {},
      "win10-x64": {},
      "win10-x64-aot": {}
    }
  }
  </code></pre>
  
  <p>The output of the command <code>dotnet -v run</code> contains this error message:</p>
  
  <pre><code>W:\src\dotnet_helloworld&gt;dotnet -v run
  ...
  W:\src\dotnet_helloworld\Program.cs(2,15): error CS0234: The type or namespace name 'Devices' does not exist in the namespace 'Windows' (are you missing an assembly reference?)
  ...
  </code></pre>