In C#, can I convert a string value to a string literal, the way I would see it in code? I would like to replace tabs, newlines, etc. with their escape sequences.
If this code:
Console.WriteLine(someString);
produces:
Hello
World!
I want this code:
Console.WriteLine(ToLiteral(someString));
to produce:
\tHello\r\n\tWorld!\r\n
A long time ago, I found this:
private static string ToLiteral(string input)
{
using (var writer = new StringWriter())
{
using (var provider = CodeDomProvider.CreateProvider("CSharp"))
{
provider.GenerateCodeFromExpression(new CodePrimitiveExpression(input), writer, null);
return writer.ToString();
}
}
}
This code:
var input = "\tHello\r\n\tWorld!";
Console.WriteLine(input);
Console.WriteLine(ToLiteral(input));
Produces:
Hello
World!
"\tHello\r\n\tWorld!"
These days, Graham discovered you can use Roslyn's Microsoft.CodeAnalysis.CSharp package on NuGet:
private static string ToLiteral(string valueTextForCompiler)
{
return Microsoft.CodeAnalysis.CSharp.SymbolDisplay.FormatLiteral(valueTextForCompiler, false);
}
A more structured approach, including all escape sequences for strings and chars, is:
It doesn't replace Unicode characters with their literal equivalent. It doesn't cook eggs, either.
public class ReplaceString
{
static readonly IDictionary<string, string> m_replaceDict
= new Dictionary<string, string>();
const string ms_regexEscapes = @"[\a\b\f\n\r\t\v\\""]";
public static string StringLiteral(string i_string)
{
return Regex.Replace(i_string, ms_regexEscapes, match);
}
public static string CharLiteral(char c)
{
return c == '\'' ? @"'\''" : string.Format("'{0}'", c);
}
private static string match(Match m)
{
string match = m.ToString();
if (m_replaceDict.ContainsKey(match))
{
return m_replaceDict[match];
}
throw new NotSupportedException();
}
static ReplaceString()
{
m_replaceDict.Add("\a", @"\a");
m_replaceDict.Add("\b", @"\b");
m_replaceDict.Add("\f", @"\f");
m_replaceDict.Add("\n", @"\n");
m_replaceDict.Add("\r", @"\r");
m_replaceDict.Add("\t", @"\t");
m_replaceDict.Add("\v", @"\v");
m_replaceDict.Add("\\", @"\\");
m_replaceDict.Add("\0", @"\0");
//The SO parser gets fooled by the verbatim version
//of the string to replace - @"\"""
//so use the 'regular' version
m_replaceDict.Add("\"", "\\\"");
}
static void Main(string[] args){
string s = "here's a \"\n\tstring\" to test";
Console.WriteLine(ReplaceString.StringLiteral(s));
Console.WriteLine(ReplaceString.CharLiteral('c'));
Console.WriteLine(ReplaceString.CharLiteral('\''));
}
}
There's a method for this in Roslyn's Microsoft.CodeAnalysis.CSharp package on NuGet:
private static string ToLiteral(string valueTextForCompiler)
{
return Microsoft.CodeAnalysis.CSharp.SymbolDisplay.FormatLiteral(valueTextForCompiler, false);
}
Obviously, this didn't exist at the time of the original question, but it might help people who end up here from Google Search.
public static class StringHelpers
{
private static Dictionary<string, string> escapeMapping = new Dictionary<string, string>()
{
{"\"", @"\\\"""},
{"\\\\", @"\\"},
{"\a", @"\a"},
{"\b", @"\b"},
{"\f", @"\f"},
{"\n", @"\n"},
{"\r", @"\r"},
{"\t", @"\t"},
{"\v", @"\v"},
{"\0", @"\0"},
};
private static Regex escapeRegex = new Regex(string.Join("|", escapeMapping.Keys.ToArray()));
public static string Escape(this string s)
{
return escapeRegex.Replace(s, EscapeMatchEval);
}
private static string EscapeMatchEval(Match m)
{
if (escapeMapping.ContainsKey(m.Value))
{
return escapeMapping[m.Value];
}
return escapeMapping[Regex.Escape(m.Value)];
}
}
Interesting question.
If you can't find a better method, you can always replace.
In case you're opting for it, you could use this C# Escape Sequence List:
This list can be found in the C# Frequently Asked Questions What character escape sequences are available?
If JSON conventions are enough for the unescaped strings you want to get escaped and you already use Json.NET (Newtonsoft.Json) in your project (it has a pretty large overhead), you may use this package like the following:
using System;
using Newtonsoft.Json;
public class Program
{
public static void Main()
{
Console.WriteLine(ToLiteral(@"abc\n123"));
}
private static string ToLiteral(string input)
{
return JsonConvert.DeserializeObject<string>("\"" + input + "\"");
}
}
My attempt at adding ToVerbatim to Hallgrim's accepted answer:
private static string ToLiteral(string input)
{
using (var writer = new StringWriter())
{
using (var provider = CodeDomProvider.CreateProvider("CSharp"))
{
provider.GenerateCodeFromExpression(new CodePrimitiveExpression(input), writer, new CodeGeneratorOptions { IndentString = "\t" });
var literal = writer.ToString();
literal = literal.Replace(string.Format("\" +{0}\t\"", Environment.NewLine), "");
return literal;
}
}
}
private static string ToVerbatim(string input)
{
string literal = ToLiteral(input);
string verbatim = "@" + literal.Replace(@"\r\n", Environment.NewLine);
return verbatim;
}
Hallgrim's answer was excellent. Here's a small tweak in case you need to parse out additional white space characters and linebreaks with a C# regular expression. I needed this in the case of a serialized JSON value for insertion into Google Sheets and ran into trouble as the code was inserting tabs, +, spaces, etc.
provider.GenerateCodeFromExpression(new CodePrimitiveExpression(input), writer, null);
var literal = writer.ToString();
var r2 = new Regex(@"\"" \+.\n[\s]+\""", RegexOptions.ECMAScript);
literal = r2.Replace(literal, "");
return literal;
Code:
string someString1 = "\tHello\r\n\tWorld!\r\n";
string someString2 = @"\tHello\r\n\tWorld!\r\n";
Console.WriteLine(someString1);
Console.WriteLine(someString2);
Output:
Hello
World!
\tHello\r\n\tWorld!\r\n