Convert a Unicode string to an escaped ASCII string

Question

How can I convert this string:

This string contains the Unicode character Pi(π)

into an escaped A

Answer 1

To store actual Unicode codepoints, you have to first decode the String's UTF-16 codeunits to UTF-32 codeunits (which are currently the same as the Unicode codepoints). Use System.Text.Encoding.UTF32.GetBytes() for that, and then write the resulting bytes to the StringBuilder as needed,i.e.

static void Main(string[] args) 
{ 
    String originalString = "This string contains the unicode character Pi(π)"; 
    Byte[] bytes = Encoding.UTF32.GetBytes(originalString);
    StringBuilder asAscii = new StringBuilder();
    for (int idx = 0; idx < bytes.Length; idx += 4)
    { 
        uint codepoint = BitConverter.ToUInt32(bytes, idx);
        if (codepoint <= 127) 
            asAscii.Append(Convert.ToChar(codepoint)); 
        else 
            asAscii.AppendFormat("\\u{0:x4}", codepoint); 
    } 
    Console.WriteLine("Final string: {0}", asAscii); 
    Console.ReadKey(); 
}