CODEWITHSUNDEEP
c#string
Radu
Radu

Reputation: 61

Evaluate escaped string

I have some strings in a file that are already escaped. So the content of the file looks like this:

Hello\nWorld. This is\tGreat.

When I read the file, I get \n as two different characters instead of one.

How can I convert an escaped string to a non-escaped one?

Upvotes: 6

Views: 4122

Answers (5)

deAtog
deAtog

Reputation: 61

Like you I was unable to find a decent solution to this problem. While you can certainly use String.Replace, the performance and speed of this solution is terrible. Furthermore, it's hard to support octal and Unicode escape sequences via this method. A much better alternative is to use a simple RegEx parser. Here's a method that will properly un-escape any string given. It supports standard escape sequences, octal escape sequences, and unicode escape sequences.

string UnEscape(string s) {
    StringBuilder sb = new StringBuilder();
    Regex r = new Regex("\\\\[abfnrtv?\"'\\\\]|\\\\[0-3]?[0-7]{1,2}|\\\\u[0-9a-fA-F]{4}|.");
    MatchCollection mc = r.Matches(s, 0);

    foreach (Match m in mc) {
        if (m.Length == 1) {
            sb.Append(m.Value);
        } else {
            if (m.Value[1] >= '0' && m.Value[1] <= '7') {
                int i = 0;

                for (int j = 1; j < m.Length; j++) {
                    i *= 8;
                    i += m.Value[j] - '0';
                }

                sb.Append((char)i);
            } else if (m.Value[1] == 'u') {
                int i = 0;

                for (int j = 2; j < m.Length; j++) {
                    i *= 16;

                    if (m.Value[j] >= '0' && m.Value[j] <= '9') {
                        i += m.Value[j] - '0';
                    } else if (m.Value[j] >= 'A' && m.Value[j] <= 'F') {
                        i += m.Value[j] - 'A' + 10;
                    } else if (m.Value[j] >= 'a' && m.Value[j] <= 'f') {
                        i += m.Value[j] - 'a' + 10;
                    }
                }

                sb.Append((char)i);
            } else {
                switch (m.Value[1]) {
                    case 'a':
                        sb.Append('\a');
                        break;
                    case 'b':
                        sb.Append('\b');
                        break;
                    case 'f':
                        sb.Append('\f');
                        break;
                    case 'n':
                        sb.Append('\n');
                        break;
                    case 'r':
                        sb.Append('\r');
                        break;
                    case 't':
                        sb.Append('\t');
                        break;
                    case 'v':
                        sb.Append('\v');
                        break;
                    default:
                        sb.Append(m.Value[1]);
                        break;
                }
            }
        }
    }

    return sb.ToString();
}

Upvotes: 3

mcdrewski
mcdrewski

Reputation: 728

based on @deAtog 's code, i made some minor additions

  • support \U00000000 format chars

  • simplify the hex conversions somewhat

    string UnEscape(string s)
{
    StringBuilder sb = new StringBuilder();
    Regex r = new Regex("\\\\[abfnrtv?\"'\\\\]|\\\\[0-3]?[0-7]{1,2}|\\\\u[0-9a-fA-F]{4}|\\\\U[0-9a-fA-F]{8}|.");
    MatchCollection mc = r.Matches(s, 0);

    foreach (Match m in mc)
    {
        if (m.Length == 1)
        {
            sb.Append(m.Value);
        }
        else
        {
            if (m.Value[1] >= '0' && m.Value[1] <= '7')
            {
                int i = Convert.ToInt32(m.Value.Substring(1), 8);
                sb.Append((char)i);
            }
            else if (m.Value[1] == 'u')
            {
                int i = Convert.ToInt32(m.Value.Substring(2), 16);
                sb.Append((char)i);
            }
            else if (m.Value[1] == 'U')
            {
                int i = Convert.ToInt32(m.Value.Substring(2), 16);
                sb.Append(char.ConvertFromUtf32(i));
            }
            else
            {
                switch (m.Value[1])
                {
                    case 'a':
                        sb.Append('\a');
                        break;
                    case 'b':
                        sb.Append('\b');
                        break;
                    case 'f':
                        sb.Append('\f');
                        break;
                    case 'n':
                        sb.Append('\n');
                        break;
                    case 'r':
                        sb.Append('\r');
                        break;
                    case 't':
                        sb.Append('\t');
                        break;
                    case 'v':
                        sb.Append('\v');
                        break;
                    default:
                        sb.Append(m.Value[1]);
                        break;
                }
            }
        }
    }

    return sb.ToString();
}

Upvotes: 8

Variant
Variant

Reputation: 17385

you could do something like:

string str = str.Replace(@"\n","\n");

update:

Obviously this is a workaround as the scenario is "un natural" by itself. The Regex.Unescape solution is unapplicable here as it is intended to use for unescaping regex control characters, and not new lines etc.

In order to support other relevant characters one can write a replacing function like this one:

public string ReEscapeControlCharacters(string str) {
   return str.Replace(@"\n","\n").Replace(@"\r","\r").Replace(@"\t","\t");
}

Upvotes: 2

Brad Christie
Brad Christie

Reputation: 101614

You can try using System.Text.RegularExpressions.Regex.Unescape.

There's also an entry on the MSDN forums.

See also How can I Unescape and Reescape strings in .net? .

Upvotes: 4

Tigran
Tigran

Reputation: 62265

Try this:

String replaced = startstring.Replace(System.Environment.NewLine, desirevalue);

This have to be valid only for "\n".

Upvotes: -3

Related Questions