String.Replace()与StringBuilder.Replace()

Question

我有一个字符串,我需要用字典中的值替换标记.它必须尽可能高效.使用string.replace执行循环只会消耗内存(字符串是不可变的,请记住).StringBuilder.Replace()会更好,因为它是用于字符串操作的吗？

我希望避免花费RegEx,但如果这样做会更有效率那么就这样吧.

注意:我不关心代码复杂性,只关心它运行的速度和消耗的内存.

平均统计数据:长度为255-1024个字符,字典中为15-30个字符.

Answer 1

使用以下代码使用RedGate Profiler

class Program
    {
        static string data = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz";
        static Dictionary<string, string> values;

        static void Main(string[] args)
        {
            Console.WriteLine("Data length: " + data.Length);
            values = new Dictionary<string, string>()
            {
                { "ab", "aa" },
                { "jk", "jj" },
                { "lm", "ll" },
                { "yz", "zz" },
                { "ef", "ff" },
                { "st", "uu" },
                { "op", "pp" },
                { "x", "y" }
            };

            StringReplace(data);
            StringBuilderReplace1(data);
            StringBuilderReplace2(new StringBuilder(data, data.Length * 2));

            Console.ReadKey();
        }

        private static void StringReplace(string data)
        {
            foreach(string k in values.Keys)
            {
                data = data.Replace(k, values[k]);
            }
        }

        private static void StringBuilderReplace1(string data)
        {
            StringBuilder sb = new StringBuilder(data, data.Length * 2);
            foreach (string k in values.Keys)
            {
                sb.Replace(k, values[k]);
            }
        }

        private static void StringBuilderReplace2(StringBuilder data)
        {
            foreach (string k in values.Keys)
            {
                data.Replace(k, values[k]);
            }
        }
    }

• String.Replace = 5.843ms
• StringBuilder.Replace#1 = 4.059ms
• Stringbuilder.Replace#2 = 0.461ms

字符串长度= 1456

stringbuilder#1在方法中创建了stringbuilder,而#2则没有,所以性能差异最终会变得相同,因为你只是将该工作移出方法.如果你从stringbuilder而不是字符串开始,那么#2可能是另一种方式.

至于内存,使用RedGateMemory分析器,在进入很多替换操作之前没有什么可担心的,其中stringbuilder将在整体上获胜.

Answer 2

这可能有所帮助:

http://blogs.msdn.com/b/debuggingtoolbox/archive/2008/04/02/comparing-regex-replace-string-replace-and-stringbuilder-replace-which-has-better-performance.aspx

简短的回答似乎是String.Replace更快,尽管它可能会对您的内存占用/垃圾收集开销产生更大的影响.

Answer 3

是的,StringBuilder会给你速度和内存的增益(主要是因为每次你用它StringBuilder来操作它都不会创建一个字符串的实例 - 总是使用相同的对象操作).这是一个MSDN链接,其中包含一些详细信息.

Answer 4

stringbuilder.replace会比String.Replace更好吗？

是的,好多了.如果你可以估计新字符串的上限(看起来你可以),那么它可能足够快.

当你创建它时:

  var sb = new StringBuilder(inputString, pessimisticEstimate);

然后StringBuilder将不必重新分配其缓冲区.