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?
based on @deAtog 's code, i made some minor additions
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();
}
You can try using System.Text.RegularExpressions.Regex.Unescape.
There's also an entry on the MSDN forums.
System.Text.RegularExpressions.Regex.Unescape. Please revise.
Regex.Unescape is unapplicable here, it is used to unescape regex control characters only.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();
}
you could do something like:
string str = str.Replace(@"\n","\n");
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");
}
\\nextTry this:
String replaced = startstring.Replace(System.Environment.NewLine, desirevalue);
This have to be valid only for "\n".
\n, not an escaped literal "slash-enn".