c#中字符串中转义字符的最快方法

我想找到最快的方法来替换字符串中所有保留字符的转义版本。

我自然而然地想到了两种朴素的方法(注意，保留字符集只是一个例子):

A:使用查找字典和字符串。替换

private Dictionary<string, string> _someEscapeTokens = new Dictionary<string, string>()
{
    {"'t", @"'t"},
    {"'n", @"'n"},
    {"'r", @"'r"}
};
public string GetEscapedStringByNaiveLookUp(string s)
{
    foreach (KeyValuePair<string, string> escapeToken in _someEscapeTokens.Where(kvp => s.Contains(kvp.Key)))
    {
        s = s.Replace(escapeToken.Key, escapeToken.Value);
    }
    return s;
}

B:遍历字符串

中的每个字符

public string GetEscapedStringByTraversingCharArray(string s)
{
    char[] chars = s.ToCharArray();
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < chars.Length; i++)
    {
        switch (chars[i])
        {
            case ''t':
                sb.Append(@"'t"); break;
            case ''n':
                sb.Append(@"'n"); break;
            case ''r':
                sb.Append(@"'r"); break;
            default:
                sb.Append(chars[i]); break;
         }
    }
    return sb.ToString();
}

正如我已经测试过的那样，版本B的性能很容易超过第一个。

注意:我已经考虑过正则表达式。转义，但由于字符集与我的不匹配，所以它不适合。

然而，有没有其他方法可以解决这个问题(考虑到性能)?

进行更多的测试

代码见下文。

在两个不同的系统上对进行了测试。. NET Framework 4.0。无论如何，结果几乎是相同的:

Char Array (short string) average time: 38600 ns
Foreach (short string) average time: 26680 ns
Char Array (long string) average time: 48,1 ms
Foreach (long string) average time: 64,2 ms
Char Array (escaping only) average time: 13,6 ms
Foreach (escaping only) average time: 17,3 ms

这让我得出结论，foreach版本对于短字符串似乎稍微快一些，但不知何故它"落在";对于更长的弦。然而，我们在这里讨论的是非常小的差异。

测试代码:

private static void Main(string[] args)
{
    //around 700 characters
    string shortString = new StackTrace().ToString();
    string longString;
    string pureEscape;
    //loading from a file with 1000000 words http://loremipsum.de/
    using (StreamReader sr = new StreamReader(@"C:'users'ekrueger'desktop'LoremIpsum.txt"))
    {
        longString = sr.ReadToEnd();
    }
    //text file containing only escapable characters (length ~1000000)
    using (StreamReader sr = new StreamReader(@"C:'users'ekrueger'desktop'PureEscape.txt"))
    {
        pureEscape = sr.ReadToEnd();
    }
    List<double> timesCharArrayShortString = new List<double>();
    List<double> timesForeachShortString = new List<double>();
    List<long> timesCharArrayLongString = new List<long>();
    List<long> timesForeachLongString = new List<long>();
    List<long> timesCharArrayPureEscape = new List<long>();
    List<long> timesForeachPureEscape = new List<long>();
    Stopwatch sw = new Stopwatch();
    for (int i = 0; i < 10; i++)
    {
        sw.Restart();
        GetEscapedStringByTraversingCharArray(shortString);
        sw.Stop();
        timesCharArrayShortString.Add(sw.Elapsed.TotalMilliseconds * 1000000);
    }
    for (int i = 0; i < 10; i++)
    {
        sw.Restart();
        GetEscapedStringForeach(shortString);
        sw.Stop();
        timesForeachShortString.Add(sw.Elapsed.TotalMilliseconds * 1000000);
    }
    for (int i = 0; i < 10; i++)
    {
        sw.Restart();
        GetEscapedStringByTraversingCharArray(longString);
        sw.Stop();
        timesCharArrayLongString.Add(sw.ElapsedMilliseconds);
    }
    for (int i = 0; i < 10; i++)
    {
        sw.Restart();
        GetEscapedStringForeach(longString);
        sw.Stop();
        timesForeachLongString.Add(sw.ElapsedMilliseconds);
    }
    for (int i = 0; i < 10; i++)
    {
        sw.Restart();
        GetEscapedStringByTraversingCharArray(pureEscape);
        sw.Stop();
        timesCharArrayPureEscape.Add(sw.ElapsedMilliseconds);
    }
    for (int i = 0; i < 10; i++)
    {
        sw.Restart();
        GetEscapedStringForeach(pureEscape);
        sw.Stop();
        timesForeachPureEscape.Add(sw.ElapsedMilliseconds);
    }
    Console.WriteLine("Char Array (short string) average time: {0} ns", timesCharArrayShortString.Average());
    Console.WriteLine("Foreach (short string) average time: {0} ns", timesForeachShortString.Average());
    Console.WriteLine("Char Array (long string) average time: {0} ms", timesCharArrayLongString.Average());
    Console.WriteLine("Foreach (long string) average time: {0} ms", timesForeachLongString.Average());
    Console.WriteLine("Char Array (escaping only) average time: {0} ms", timesCharArrayPureEscape.Average());
    Console.WriteLine("Foreach (escaping only) average time: {0} ms", timesForeachPureEscape.Average());
    Console.Read();
}
private static string GetEscapedStringByTraversingCharArray(string s)
{
    if (String.IsNullOrEmpty(s))
        return s;
    char[] chars = s.ToCharArray();
    StringBuilder sb = new StringBuilder(s.Length);
    for (int i = 0; i < chars.Length; i++)
    {
        switch (chars[i])
        {
            case ''t':
                sb.Append(@"'t"); break;
            case ''n':
                sb.Append(@"'n"); break;
            case ''r':
                sb.Append(@"'r"); break;
            case ''f':
                sb.Append(@"'f"); break;
            default:
                sb.Append(chars[i]); break;
        }
    }
    return sb.ToString();
}
public static string GetEscapedStringForeach(string s)
{
    if (String.IsNullOrEmpty(s))
        return s;
    StringBuilder sb = new StringBuilder(s.Length);
    foreach (Char ch in s)
    {
        switch (ch)
        {
            case ''t':
                sb.Append(@"'t"); break;
            case ''n':
                sb.Append(@"'n"); break;
            case ''r':
                sb.Append(@"'r"); break;
            default:
                sb.Append(ch); break;
        }
    }
    return sb.ToString();
}

public string GetEscapedStringByTraversingCharArray(string s) {
  // do not forget about null...
  if (String.IsNullOrEmpty(s))
    return s;
  // we can be sure, that it requires at least s.Length symbols, let's allocate then
  // in case we want to trade memory for speed we can even put
  //   StringBuilder sb = new StringBuilder(2 * s.Length);
  // for the worst case when all symbols should be escaped
  StringBuilder sb = new StringBuilder(s.Length);
  foreach(Char ch in s) {
    switch (ch) {
      case ''t':
        sb.Append(@"'t"); 
        break;
      case ''n':
        sb.Append(@"'n"); 
        break;
      case ''r':
        sb.Append(@"'r"); 
        break;
      default:
        sb.Append(ch); 
        break;
    }
  }
  return sb.ToString();
}

s = s.Replace(escapeToken.Key, escapeToken.Value);