What does Console.WriteLine() call behind the scenes? [closed]

Question

I'm interested in how calling Console.WriteLine() actually displays text.

I've had a look at the source code from: http://referencesource.microsoft.com/#mscorlib/system/io/textwriter.cs,5f99350fdf8dae53 and can see that this method from TextWriter ends up getting called:

        // Writes a character to the text stream. This default method is empty,
        // but descendant classes can override the method to provide the
        // appropriate functionality.
        //
        public virtual void Write(char value) {
        }

What is the descendant class that overrides this method? And what is the implementation?

Answer 1

Check out the source from the CoreCLR branch, which Microsoft are hosting on github:

    [SecuritySafeCritical]
    static Console()
    {
        _outputHandle = new SafeFileHandle(Win32Native.GetStdHandle(Win32Native.STD_OUTPUT_HANDLE), false);
    }

    [SecuritySafeCritical]
    public static unsafe void Write(string s)
    {
        byte[] bytes = Encoding.UTF8.GetBytes(s);
        fixed (byte * pBytes = bytes)
        {
            int bytesWritten;
            Win32Native.WriteFile(_outputHandle, pBytes, bytes.Length, out bytesWritten, IntPtr.Zero);
        }
    }

There are two things going on here: in the static ctor, the code is getting a Win32 handle to the STD_OUTPUT virtual file, which wraps the standard output to the process's attached console. And in the Write method, it's writing the data to that file.

Basically, it wraps the internal OS facilities for writing to a console, which is virtual file.

Answer 2

Based on the reference source:

• Console.WriteLine(string) calls Console.Out.WriteLine(string)
• Console.Out is initialized by calling InitializeStdOutError(true)
• InitializeStdOutError returns a TextWriter.Synchronized wrapper around a StreamWriter wrapper (with AutoFlush enabled) around a Stream returned by OpenStandardOutput
• OpenStandardOutput calls GetStandardFile with stdHandleName of STD_OUTPUT_HANDLE
• GetStandardFile calls the Win32 native function GetStdHandle, wraps the returned handle in SafeFileHandle and then wraps the SafeFileHandle in __ConsoleStream
• TextWriter.Synchronized returns a SyncTextWriter
• SyncTextWriter.WriteLine(string) calls WriteLine(string) on the underlying StreamWriter
• StreamWriter does not override WriteLine(string), so it inherits the implementation from its base class, TextWriter
• TextWriter.WriteLine(string) calls Write(char[], int, int)
• StreamWriter.Write(char[], int, int) copies the characters to an internal buffer and then calls Flush()
• StreamWriter.Flush() encodes characters from the internal buffer into bytes and then calls Write(byte[], int, int) and Flush() on the underlying __ConsoleStream
• __ConsoleStream.Write(byte[], int, int) calls WriteFileNative
• __ConsoleStream.WriteFileNative calls the Win32 native function WriteFile or WriteConsoleW