Escape Unicode characters in ASCII string

In some programming scenarios, converting Unicode characters to escaped ASCII strings is a common requirement. This process allows Unicode characters to be preserved, otherwise it may be lost or replaced by other characters during the encoding process.

For example, a string containing the Unicode character π (Pi) needs to be converted to escaped ASCII format (\u03a0). This conversion ensures that characters are preserved even if the string is encoded in systems that do not support Unicode characters.

To do this, any non-ASCII characters in the string need to be replaced with their corresponding escape sequence. These escape sequences begin with a backslash (\) followed by a hexadecimal representation of Unicode code points. For example, the Unicode code point of π is 03a0, so its escape sequence becomes \u03a0.

The following C# code demonstrates how to encode and decode non-ASCII characters using \uXXXX escape format:

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main(string[] args)
    {
        string unicodeString = "此函数包含一个Unicode字符pi (\u03a0)";

        Console.WriteLine(unicodeString);

        string encoded = EncodeNonAsciiCharacters(unicodeString);
        Console.WriteLine(encoded);

        string decoded = DecodeEncodedNonAsciiCharacters(encoded);
        Console.WriteLine(decoded);
    }

    static string EncodeNonAsciiCharacters(string value)
    {
        StringBuilder sb = new StringBuilder();
        foreach (char c in value)
        {
            if (c > 127)
            {
                // 此字符对于ASCII来说太大
                string encodedValue = "\\u"   ((int)c).ToString("x4");
                sb.Append(encodedValue);
            }
            else
            {
                sb.Append(c);
            }
        }
        return sb.ToString();
    }

    static string DecodeEncodedNonAsciiCharacters(string value)
    {
        return Regex.Replace(
            value,
            @"\\u(?[a-zA-Z0-9]{4})",
            m =>
            {
                return ((char)int.Parse(m.Groups["Value"].Value, NumberStyles.HexNumber)).ToString();
            });
    }
}

In this code, the EncodeNonAsciiCharacters method traverses the input string and recognizes non-ASCII characters, converting them into their escape sequence. On the other hand, the DecodeEncodedNonAsciiCharacters method uses a regular expression to parse escaped strings and converts them back to the original Unicode characters.

The output of this program demonstrates the process:

此函数包含一个Unicode字符pi (π)
此函数包含一个Unicode字符pi (\u03a0)
此函数包含一个Unicode字符pi (π)