Develop Reference

Unhandled Exception: System.InvalidOperationException: Stack empty

I'm learning data structures so I'm trying to implement expression evaluation using stack in two steps (convert infix expression to postfix then use the result of it to evaluate postfix)
but I keep getting this error :
Unhandled Exception: System.InvalidOperationException: Stack empty.
at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
at System.Collections.Generic.Stack`1.Pop()
at DataStructures.StackArray.evaluatePostfix(String exp) in E:\visual studio c#\New folder\DataStructures\StackArray.cs:line 281
at DataStructures.Program.Main(String[] args) in E:\visual studio c#\New folder\DataStructures\Program.cs:line 71
I definitely miss something silly for some reason so I'll appreciate any advice.
public static string infixToPostfix(string exp)
{
var postFix = "";
Stack<char> Stack = new Stack<char>();
for(int i = 0; i < exp.Length; ++i)
{
char x = exp[i];
// If the scanned character is an operand, add it to output.
if (char.IsLetterOrDigit(x))
{
postFix += x;
}
//parentheses part
else if (x == '(')
{
Stack.Push(x);
}
else if (x == ')')
{
while (Stack.Count>0 && Stack.Peek() != '(')
{
postFix += Stack.Pop();
}
if(Stack.Peek() == '(')
{
Stack.Pop();
}
}
else
{
while (Stack.Count > 0 && x <= Precedence(Stack.Peek()))
{
postFix += Stack.Pop();
}
Stack.Push(x);
}
}
//pop the remain of stack
while(Stack.Count > 0)
{
postFix += Stack.Pop();
}
return postFix;
}
/////////////////////////////////////////////////////
public static int evaluatePostfix(string exp)
{
Stack<int> Stack = new Stack<int>();
for(int i = 0; i < exp.Length; i++)
{
char x = exp[i];
//if "x" whitespace
if (x == ' ')
{
//skip it
continue;
}
else if (char.IsDigit(x))
{
//create new variable to store the extracted numbers in it
int num = 0;
while (char.IsDigit(x))
{
num = num * 10 + (int)(x - '0');
i++;
x = exp[i];
}
i--;
Stack.Push(num);
}
else
{
//create two vaiables to present the two elements
int v1 = Stack.Pop();
int v2 = Stack.Pop();
// Perform arithmetic operations between 2 operands
switch (x)
{
case '+':
Stack.Push(v2 + v1);
break;
case '-':
Stack.Push(v2 - v1);
break;
case '/':
Stack.Push(v2 / v1);
break;
case '*':
Stack.Push(v2 * v1);
break;
}
}
}
return Stack.Pop();
}
main method:
static void Main(string[] args)
{
var infix = Console.ReadLine();
string postFix;
var r = StackArray.infixToPostfix(infix);
Console.WriteLine($"postfix is {r}");
//evaluate postfiix
int x = StackArray.evaluatePostfix(r);
Console.WriteLine($"result is {x}");
}

Is it possible to escape Json string using System.Text.Json [duplicate]

Are there any classes/functions available to be used for easy JSON escaping? I'd rather not have to write my own.

I use System.Web.HttpUtility.JavaScriptStringEncode
string quoted = HttpUtility.JavaScriptStringEncode(input);

For those using the very popular Json.Net project from Newtonsoft the task is trivial:
using Newtonsoft.Json;
....
var s = JsonConvert.ToString(#"a\b");
Console.WriteLine(s);
....
This code prints:
"a\\b"
That is, the resulting string value contains the quotes as well as the escaped backslash.

Building on the answer by Dejan, what you can do is import System.Web.Helpers .NET Framework assembly, then use the following function:
static string EscapeForJson(string s) {
string quoted = System.Web.Helpers.Json.Encode(s);
return quoted.Substring(1, quoted.Length - 2);
}
The Substring call is required, since Encode automatically surrounds strings with double quotes.

Yep, just add the following function to your Utils class or something:
public static string cleanForJSON(string s)
{
if (s == null || s.Length == 0) {
return "";
}
char c = '\0';
int i;
int len = s.Length;
StringBuilder sb = new StringBuilder(len + 4);
String t;
for (i = 0; i < len; i += 1) {
c = s[i];
switch (c) {
case '\\':
case '"':
sb.Append('\\');
sb.Append(c);
break;
case '/':
sb.Append('\\');
sb.Append(c);
break;
case '\b':
sb.Append("\\b");
break;
case '\t':
sb.Append("\\t");
break;
case '\n':
sb.Append("\\n");
break;
case '\f':
sb.Append("\\f");
break;
case '\r':
sb.Append("\\r");
break;
default:
if (c < ' ') {
t = "000" + String.Format("X", c);
sb.Append("\\u" + t.Substring(t.Length - 4));
} else {
sb.Append(c);
}
break;
}
}
return sb.ToString();
}

I have used following code to escape the string value for json.
You need to add your '"' to the output of the following code:
public static string EscapeStringValue(string value)
{
const char BACK_SLASH = '\\';
const char SLASH = '/';
const char DBL_QUOTE = '"';
var output = new StringBuilder(value.Length);
foreach (char c in value)
{
switch (c)
{
case SLASH:
output.AppendFormat("{0}{1}", BACK_SLASH, SLASH);
break;
case BACK_SLASH:
output.AppendFormat("{0}{0}", BACK_SLASH);
break;
case DBL_QUOTE:
output.AppendFormat("{0}{1}",BACK_SLASH,DBL_QUOTE);
break;
default:
output.Append(c);
break;
}
}
return output.ToString();
}

In .Net Core 3+ and .Net 5+:
string escapedJsonString = JsonEncodedText.Encode(jsonString);

The methods offered here are faulty.
Why venture that far when you could just use System.Web.HttpUtility.JavaScriptEncode ?
If you're on a lower framework, you can just copy paste it from mono
Courtesy of the mono-project #
https://github.com/mono/mono/blob/master/mcs/class/System.Web/System.Web/HttpUtility.cs
public static string JavaScriptStringEncode(string value, bool addDoubleQuotes)
{
if (string.IsNullOrEmpty(value))
return addDoubleQuotes ? "\"\"" : string.Empty;
int len = value.Length;
bool needEncode = false;
char c;
for (int i = 0; i < len; i++)
{
c = value[i];
if (c >= 0 && c <= 31 || c == 34 || c == 39 || c == 60 || c == 62 || c == 92)
{
needEncode = true;
break;
}
}
if (!needEncode)
return addDoubleQuotes ? "\"" + value + "\"" : value;
var sb = new System.Text.StringBuilder();
if (addDoubleQuotes)
sb.Append('"');
for (int i = 0; i < len; i++)
{
c = value[i];
if (c >= 0 && c <= 7 || c == 11 || c >= 14 && c <= 31 || c == 39 || c == 60 || c == 62)
sb.AppendFormat("\\u{0:x4}", (int)c);
else switch ((int)c)
{
case 8:
sb.Append("\\b");
break;
case 9:
sb.Append("\\t");
break;
case 10:
sb.Append("\\n");
break;
case 12:
sb.Append("\\f");
break;
case 13:
sb.Append("\\r");
break;
case 34:
sb.Append("\\\"");
break;
case 92:
sb.Append("\\\\");
break;
default:
sb.Append(c);
break;
}
}
if (addDoubleQuotes)
sb.Append('"');
return sb.ToString();
}
This can be compacted into
// https://github.com/mono/mono/blob/master/mcs/class/System.Json/System.Json/JsonValue.cs
public class SimpleJSON
{
private static bool NeedEscape(string src, int i)
{
char c = src[i];
return c < 32 || c == '"' || c == '\\'
// Broken lead surrogate
|| (c >= '\uD800' && c <= '\uDBFF' &&
(i == src.Length - 1 || src[i + 1] < '\uDC00' || src[i + 1] > '\uDFFF'))
// Broken tail surrogate
|| (c >= '\uDC00' && c <= '\uDFFF' &&
(i == 0 || src[i - 1] < '\uD800' || src[i - 1] > '\uDBFF'))
// To produce valid JavaScript
|| c == '\u2028' || c == '\u2029'
// Escape "</" for <script> tags
|| (c == '/' && i > 0 && src[i - 1] == '<');
}
public static string EscapeString(string src)
{
System.Text.StringBuilder sb = new System.Text.StringBuilder();
int start = 0;
for (int i = 0; i < src.Length; i++)
if (NeedEscape(src, i))
{
sb.Append(src, start, i - start);
switch (src[i])
{
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 '\"': sb.Append("\\\""); break;
case '\\': sb.Append("\\\\"); break;
case '/': sb.Append("\\/"); break;
default:
sb.Append("\\u");
sb.Append(((int)src[i]).ToString("x04"));
break;
}
start = i + 1;
}
sb.Append(src, start, src.Length - start);
return sb.ToString();
}
}

I ran speed tests on some of these answers for a long string and a short string. Clive Paterson's code won by a good bit, presumably because the others are taking into account serialization options. Here are my results:
Apple Banana
System.Web.HttpUtility.JavaScriptStringEncode: 140ms
System.Web.Helpers.Json.Encode: 326ms
Newtonsoft.Json.JsonConvert.ToString: 230ms
Clive Paterson: 108ms
\\some\long\path\with\lots\of\things\to\escape\some\long\path\t\with\lots\of\n\things\to\escape\some\long\path\with\lots\of\"things\to\escape\some\long\path\with\lots"\of\things\to\escape
System.Web.HttpUtility.JavaScriptStringEncode: 2849ms
System.Web.Helpers.Json.Encode: 3300ms
Newtonsoft.Json.JsonConvert.ToString: 2827ms
Clive Paterson: 1173ms
And here is the test code:
public static void Main(string[] args)
{
var testStr1 = "Apple Banana";
var testStr2 = #"\\some\long\path\with\lots\of\things\to\escape\some\long\path\t\with\lots\of\n\things\to\escape\some\long\path\with\lots\of\""things\to\escape\some\long\path\with\lots""\of\things\to\escape";
foreach (var testStr in new[] { testStr1, testStr2 })
{
var results = new Dictionary<string,List<long>>();
for (var n = 0; n < 10; n++)
{
var count = 1000 * 1000;
var sw = Stopwatch.StartNew();
for (var i = 0; i < count; i++)
{
var s = System.Web.HttpUtility.JavaScriptStringEncode(testStr);
}
var t = sw.ElapsedMilliseconds;
results.GetOrCreate("System.Web.HttpUtility.JavaScriptStringEncode").Add(t);
sw = Stopwatch.StartNew();
for (var i = 0; i < count; i++)
{
var s = System.Web.Helpers.Json.Encode(testStr);
}
t = sw.ElapsedMilliseconds;
results.GetOrCreate("System.Web.Helpers.Json.Encode").Add(t);
sw = Stopwatch.StartNew();
for (var i = 0; i < count; i++)
{
var s = Newtonsoft.Json.JsonConvert.ToString(testStr);
}
t = sw.ElapsedMilliseconds;
results.GetOrCreate("Newtonsoft.Json.JsonConvert.ToString").Add(t);
sw = Stopwatch.StartNew();
for (var i = 0; i < count; i++)
{
var s = cleanForJSON(testStr);
}
t = sw.ElapsedMilliseconds;
results.GetOrCreate("Clive Paterson").Add(t);
}
Console.WriteLine(testStr);
foreach (var result in results)
{
Console.WriteLine(result.Key + ": " + Math.Round(result.Value.Skip(1).Average()) + "ms");
}
Console.WriteLine();
}
Console.ReadLine();
}

I would also recommend using the JSON.NET library mentioned, but if you have to escape unicode characters (e.g. \uXXXX format) in the resulting JSON string, you may have to do it yourself. Take a look at Converting Unicode strings to escaped ascii string for an example.

I nice one-liner, used JsonConvert as others have but added substring to remove the added quotes and backslash.
var escapedJsonString = JsonConvert.ToString(JsonString).Substring(1, JsonString.Length - 2);

What about System.Web.Helpers.Json.Encode(...) (see http://msdn.microsoft.com/en-us/library/system.web.helpers.json.encode(v=vs.111).aspx)?

String.Format("X", c);
That just outputs: X
Try this instead:
string t = ((int)c).ToString("X");
sb.Append("\\u" + t.PadLeft(4, '0'));

There's a Json library at Codeplex

I chose to use System.Web.Script.Serialization.JavaScriptSerializer.
I have a small static helper class defined as follows:
internal static partial class Serialization
{
static JavaScriptSerializer serializer;
static Serialization()
{
serializer = new JavaScriptSerializer();
serializer.MaxJsonLength = Int32.MaxValue;
}
public static string ToJSON<T>(T obj)
{
return serializer.Serialize(obj);
}
public static T FromJSON<T>(string data)
{
if (Common.IsEmpty(data))
return default(T);
else
return serializer.Deserialize<T>(data);
}
}
To serialize anything I just call Serialization.ToJSON(itemToSerialize)
To deserialize I just call Serialization.FromJSON<T>(jsonValueOfTypeT)

Identifing number of character/digits/special character in string

I want to calculate the summary of string in terms of number of alphabets, digits and special character in C#. For example:
String abc123$% should have summary like A3D3S2 (which means 3 Alphabet, 3 Digits and 2 Special character)
a34=$# should have summary like A1D2S3 (which means 1 Alphabet, 2 Digits and 3 Special character)
a3b$s should have summary like A1D1A1S1A1 (which means 1 Alphabet, 1 Digits,1 Alphabet, 1 Special character,1 Alphabet)
Can anyone guide me how can write an algorithm which can perform the above task in a quick way? as I think if I search the string character by character, then it will take considerable amount of time. and I have a large dataset of strings.

This works:
static string GetSummary(string input)
{
var sb = new StringBuilder();
string prevMode = "";
string curMode = "";
int sameModeCount = 0;
for (int i = 0; i <= input.Length; ++i)
{
if (i < input.Length)
{
char c = input[i];
if ('a' <= c && c <= 'z' || 'A' <= c && c <= 'Z')
{
curMode = "A";
}
else if ('0' <= c && c <= '9')
{
curMode = "D";
}
else
{
curMode = "S";
}
}
else
{
curMode = "";
}
if (curMode != prevMode && prevMode != "")
{
sb.Append(prevMode);
sb.Append(sameModeCount);
sameModeCount = 0;
}
prevMode = curMode;
++sameModeCount;
}
return sb.ToString();
}
Test:
public static void Main()
{
Console.WriteLine(GetSummary("abc123$%"));
Console.WriteLine(GetSummary("a34=$#"));
Console.WriteLine(GetSummary("a3b$s"));
}
Results:
A3D3S2
A1D2S3
A1D1A1S1A1

With Linq, you can do like this :
string myinput = "abc123$%";
int letter =0 , digit = 0, specialCharacter = 0;
myinput.ToCharArray().ToList().ForEach(x =>
{
letter = Char.IsLetter(x) ? ++letter : letter;
digit = Char.IsDigit(x) ? ++digit : digit;
specialCharacter = !Char.IsLetterOrDigit(x) ?
++specialCharacter : specialCharacter;
});
string formattedVal = String.Format("A{0}D{1}S{2}", letter, digit,
specialCharacter);
You can directly use array in Linq ForEach without converting to list by :
Array.ForEach(myinput.ToCharArray(), x =>
{
letter = Char.IsLetter(x) ? ++letter : letter;
digit = Char.IsDigit(x) ? ++digit : digit;
specialCharacter = !Char.IsLetterOrDigit(x) ? ++specialCharacter : specialCharacter;
});
string formattedVal = String.Format("A{0}D{1}S{2}", letter, digit, specialCharacter);

This should work:
string s = "a3b$s";
char etype = 'X'; //current character's type
char etypeinit = 'X'; //tracker variable - holds type of last character
string str = "";
int count = 1;
foreach(char c in s)
{
//Use this block of conditionals to assign type for current character
if(char.IsLetter(c))
{
etype = 'A';
}
else if(char.IsDigit(c))
{
etype = 'D';
}
else
{
etype = 'S';
}
//This is a different type of character compared to the previous one
if(etypeinit != etype)
{
str += string.Format("{0}{1}",etype,count); //Build the string
count = 1; //Reset count
}
else
{
count++; //Increment because this is the same type as previous one
}
etypeinit = etype; //Set tracker variable to type of current character
}
Console.WriteLine(str);

Little late and little complex but able to produces all expected output as per given inputs in the question, please take a look:
string inputString = "abc123$%ab12";
var results = inputString.Select(x => char.IsLetter(x) ? 'A' :
char.IsDigit(x) ? 'D' : 'S');
StringBuilder outPutBuilder = new StringBuilder();
char previousChar = results.First();
int charCount = 0;
foreach (var item in results)
{
switch (item)
{
case 'A':
if (previousChar == 'A')
{
charCount++;
}
else
{
outPutBuilder.Append(previousChar.ToString() + charCount);
charCount = 1;
}
break;
case 'D':
if (previousChar == 'D')
charCount++;
else
{
outPutBuilder.Append(previousChar.ToString() + charCount);
charCount = 1;
}
break;
default:
if (previousChar == 'S')
charCount++;
else
{
outPutBuilder.Append(previousChar.ToString() + charCount);
charCount = 1;
}
break;
}
previousChar = item;
}
outPutBuilder.Append(previousChar.ToString() + charCount);
Working example

Use a FOR loop to go through each character. If the character is in the range of a-z or A-Z then it is an alphabet. If in the range of 0-9 then it is a digit else special character.
Code
string inputStr = "a3b$s";
string outputStr = string.Empty;
char firstChar = Convert.ToChar(inputStr.Substring(0, 1));
outputStr = char.IsLetter(firstChar) ? "A1" : char.IsDigit(firstChar) ? "D1" : "S1";
for (int i = 1; i < inputStr.Length; i++)
{
char nextChar = char.IsLetter(inputStr[i]) ? 'A' :
char.IsDigit(inputStr[i]) ? 'D' : 'S';
char prevChar = Convert.ToChar(outputStr.Substring(outputStr.Length - 2, 1));
if (nextChar == prevChar)
{
int lastDig = Convert.ToInt32(outputStr.Substring(outputStr.Length - 1, 1));
outputStr = outputStr.Substring(0, outputStr.Length - 1) +
(lastDig + 1).ToString();
}
else
outputStr += nextChar.ToString() + "1";
}
Console.WriteLine(outputStr.ToString());
Output
A1D1A1S1A1
Find demo here

Incrementing an alphanumeric string [duplicate]

This question already has answers here:
Iterating through the Alphabet - C# a-caz
(10 answers)
Closed 8 years ago.
I am trying to increment an alphanumeric string using a given charset
say the input is 0000a
then the output should be 0000b
However when the input reaches the defined limit, say zzzzz
it should reset to 00001
I have read the following Increment of Alphabet in c#
using
char c
c++
seem to be the best way to do this.
I have the following class
Namespace BatchNo_Generator
{
class RandomStringGenerator
{
public enum Mode
{
ALPHANUMERIC = 1,
ALPHA = 2,
NUMERIC = 3,
}
public string genbase(int length, string mode)
{
int j = 0;
if (mode == "ALPHANUMERIC")
{
StringBuilder s = new StringBuilder();
while (j < length - 1)
{
s.Insert(0, "0");
j++;
}
s.Insert(s.Length, "1");
return s.ToString();
}
if (mode == "ALPHA")
{
StringBuilder s = new StringBuilder();
while (j < length - 1)
{
s.Insert(0, "a");
j++;
}
s.Insert(s.Length, "a");
return s.ToString();
}
if (mode == "NUMERIC")
{
StringBuilder s = new StringBuilder();
while (j < length - 1)
{
s.Insert(0, "0");
j++;
}
s.Insert(s.Length, "1");
return s.ToString();
}
return "";
}
public string gennext(string current, string mode, char endchar)
{
StringBuilder s = new StringBuilder(current);
int i = current.Length;
if (mode == "ALPHA")
{
for (int j = i; j > 0; j--)
{
if (checkend(s[j - 1], endchar, 'a', mode) == true)
{
s[j] = resetchar(s[j], 'a');
incrementchar(s[j + 1], mode);
}
else
{
char c = incrementchar(s[j - 1], mode);
s.Remove(j - 1, 1);
s.Insert(j - 1, c);
break;
}
}
return s.ToString();
}
if (mode == "NUMERIC")
{
for (int j = i; j > 0; j--)
{
if (checkend(s[j - 1], endchar, '0', mode) == true)
{
s[j-1] = resetchar(s[j-1], '0');
incrementchar(s[j - 1], mode);
}
else
{
char c = incrementchar(s[j - 1], mode);
s.Remove(j - 1, 1);
s.Insert(j - 1, c);
}
}
return s.ToString();
}
if (mode == "ALPHANUMERIC")
{
for (int j = i; j > 0; j--)
{
if (checkend(s[j - 1], endchar, '0', mode) == true)
{
s[j-1] = resetchar(s[j-1], '0');
char c = incrementchar(s[j - 1], mode);
}
else
{
{
char c = incrementchar(s[j - 1], mode);
s.Remove(j - 1, 1);
s.Insert(j - 1, c);
break;
}
}
}
return s.ToString();
}
return "";
}
public char incrementchar(char c, string mode)
{
char cnew = c++;
switch (mode)
{
case "ALPHA":
{
if (char.IsLetter(c) == false) { cnew++; }
else { return char.ToLower(c); }
break;
}
case "NUMERIC":
{
if (char.IsDigit(c) == false) { cnew++; }
else { return c; }
break;
}
case "ALPHANUMERIC":
{
while (char.IsLetterOrDigit(c) == false) { c++; }
// if (char.IsLetterOrDigit(c) == false) { cnew++; }
// else { return char.ToLower(c); }
return char.ToLower(c);
break;
}
}
return '?';
}
public bool checkend(char current, char end, char start, string mode)
{
if (current == end) { return true; }
else { return false; }
}
public char resetchar(char inputchar, char defaultchar)
{
return defaultchar;
}
public static IEnumerable<string> GetColumns(char startchar, char endchar)
{
string s = null;
for (char c2 = startchar; c2 <= endchar + 1; c2++)
{
for (char c = 'A'; c <= 'Z'; c++)
{
if (char.IsLetter(c) == true)
{
yield return s + char.ToLower(c);
}
}
if (char.IsLetterOrDigit(c2) == true)
{
s = c2.ToString();
}
}
}
}
}
Which I tried with
RandomStringGenerator test = new RandomStringGenerator();
MessageBox.Show(test.gennext("0zzzz","ALPHANUMERIC",'0'));
The issue I have is that this input 0zzzz returns 0zzzª
Any help would be appreciated
The code is sloppy I know, i will be cleaning it up when I get a working set

public enum Mode
{
AlphaNumeric = 1,
Alpha = 2,
Numeric = 3
}
public static string Increment(string text, Mode mode)
{
var textArr = text.ToCharArray();
// Add legal characters
var characters = new List<char>();
if (mode == Mode.AlphaNumeric || mode == Mode.Numeric)
for (char c = '0'; c <= '9'; c++)
characters.Add(c);
if (mode == Mode.AlphaNumeric || mode == Mode.Alpha)
for (char c = 'a'; c <= 'z'; c++)
characters.Add(c);
// Loop from end to beginning
for (int i = textArr.Length - 1; i >= 0; i--)
{
if (textArr[i] == characters.Last())
{
textArr[i] = characters.First();
}
else
{
textArr[i] = characters[characters.IndexOf(textArr[i]) + 1];
break;
}
}
return new string(textArr);
}
// Testing
var test1 = Increment("0001", Mode.AlphaNumeric);
var test2 = Increment("aab2z", Mode.AlphaNumeric);
var test3 = Increment("0009", Mode.Numeric);
var test4 = Increment("zz", Mode.Alpha);
var test5 = Increment("999", Mode.Numeric);

Best way to put user input into generated javascript?

I need for someone to be able to put some text into a page and then this gets sent to the server, saved in the database, and else where this text is put into a javascript variable.
Basically like this:
Write("var myVar=\""+MyData+"\";");
What is the best way of escaping this data? Is there anything out there already to deal with things like ' and " and new lines? Is base64 my only option?
My serverside framework/language is ASP.Net/C#

You should use WPL:
Write("var myVar=" + Encoder.JavaScriptEncode(MyData, true) + ";");
if you don't want to reference the library, you can use the following function (adapted from the .Net source):
public static void QuoteString(this string value, StringBuilder b) {
if (String.IsNullOrEmpty(value))
return "";
var b = new StringBuilder();
int startIndex = 0;
int count = 0;
for (int i = 0; i < value.Length; i++) {
char c = value[i];
// Append the unhandled characters (that do not require special treament)
// to the string builder when special characters are detected.
if (c == '\r' || c == '\t' || c == '\"' || c == '\'' || c == '<' || c == '>' ||
c == '\\' || c == '\n' || c == '\b' || c == '\f' || c < ' ') {
if (b == null) {
b = new StringBuilder(value.Length + 5);
}
if (count > 0) {
b.Append(value, startIndex, count);
}
startIndex = i + 1;
count = 0;
}
switch (c) {
case '\r':
b.Append("\\r");
break;
case '\t':
b.Append("\\t");
break;
case '\"':
b.Append("\\\"");
break;
case '\\':
b.Append("\\\\");
break;
case '\n':
b.Append("\\n");
break;
case '\b':
b.Append("\\b");
break;
case '\f':
b.Append("\\f");
break;
case '\'':
case '>':
case '<':
AppendCharAsUnicode(b, c);
break;
default:
if (c < ' ') {
AppendCharAsUnicode(b, c);
} else {
count++;
}
break;
}
}
if (b == null) {
b.Append(value);
}
if (count > 0) {
b.Append(value, startIndex, count);
}
return b.ToString();
}