StringBuilder的与字符串连接 [英] stringbuilder versus string concat

问题描述

在我的项目，我在整个循环数据视图的结果。

In my project I am looping across a dataview result.

 string html =string.empty;
 DataView dV = data.DefaultView;
 for(int i=0;i< dV.Count;i++)
 {
     DataRowView rv = dV[i];
     html += rv.Row["X"].Tostring();
 }

以DV的行数将永久被3或4。

Number of rows in dV will alway be 3 or 4.

是更好地使用字符串连接+ = opearator或StringBuilder的这种情况下，为什么？

Is it better to use the string concat += opearator or StringBuilder for this case and why?

推荐答案

我会使用的StringBuilder 在这里，只是因为它描述你在做什么。

I would use StringBuilder here, just because it describes what you're doing.

有关的3或4串的简单拼接，它可能不会作出任何显著差异，字符串连接的可能的连稍微快一点 - 但如果你错了，还有的地段的行，的StringBuilder 将开始变得更加高效，而且它的总是的更具描述性的，你在做什么。

For a simple concatenation of 3 or 4 strings, it probably won't make any significant difference, and string concatenation may even be slightly faster - but if you're wrong and there are lots of rows, StringBuilder will start getting much more efficient, and it's always more descriptive of what you're doing.

另外，使用这样的：

string html = string.Join("", dv.Cast<DataRowView>()
                                .Select(rv => rv.Row["X"]));

请注意，你没有任何的排序此刻的字符串之间的分隔符的。你确定这就是你想要什么？ （另请注意，您的code没有在此刻做出了很大的意义 - ？你不使用 I 在循环为什么）

Note that you don't have any sort of separator between the strings at the moment. Are you sure that's what you want? (Also note that your code doesn't make a lot of sense at the moment - you're not using i in the loop. Why?)

我对字符串连接的文章肚里的更多细节的为什么它使用的StringBuilder 时的价值。

I have an article about string concatenation which goes into more detail about why it's worth using StringBuilder and when.

编辑：对于那些谁怀疑字符串连接可以更快，这里是一个考验 - 与故意肮脏的数据，但只是为了证明这是可能的：

For those who doubt that string concatenation can be faster, here's a test - with deliberately "nasty" data, but just to prove it's possible:

using System;
using System.Diagnostics;
using System.Text;

class Test
{
    static readonly string[] Bits = { 
        "small string",
        "string which is a bit longer",
        "stirng which is longer again to force yet another copy with any luck"
    };

    static readonly int ExpectedLength = string.Join("", Bits).Length;

    static void Main()        
    {
        Time(StringBuilderTest);
        Time(ConcatenateTest);
    }

    static void Time(Action action)
    {
        GC.Collect();
        GC.WaitForPendingFinalizers();
        GC.Collect();
        // Make sure it's JITted
        action();
        Stopwatch sw = Stopwatch.StartNew();
        for (int i = 0; i < 10000000; i++)
        {
            action();
        }
        sw.Stop();
        Console.WriteLine("{0}: {1} millis", action.Method.Name,
                          (long) sw.Elapsed.TotalMilliseconds);
    }

    static void ConcatenateTest()
    {
        string x = "";
        foreach (string bit in Bits)
        {
            x += bit;
        }
        // Force a validation to prevent dodgy optimizations
        if (x.Length != ExpectedLength)
        {
            throw new Exception("Eek!");
        }
    }

    static void StringBuilderTest()
    {
        StringBuilder builder = new StringBuilder();
        foreach (string bit in Bits)
        {
            builder.Append(bit);
        }
        string x = builder.ToString();
        // Force a validation to prevent dodgy optimizations
        if (x.Length != ExpectedLength)
        {
            throw new Exception("Eek!");
        }
    }
}

在我的机器上的结果（编译 / O + /调试 - ）

StringBuilderTest: 2245 millis
ConcatenateTest: 989 millis

我已经运行了好几次，包括扭转测试的顺序，结果是一致的。

I've run this several times, including reversing the order of the tests, and the results are consistent.

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