StringBuilder String string.Concat 字符串拼接速度再议_.NET_编程开发_程序员俱乐部

首先看测试代码：

 1   public class StringSpeedTest
 2     {
 3         private readonly static string _testStr = "0123456789";
 4 
 5         public string StringAdd(int count)
 6         {
 7             string str = string.Empty;
 8             for (int i = 0; i < count; i++)
 9             {
10                 str += _testStr;
11             }
12             return str;
13         }
14 
15         public string UseStringBuilder(int count)
16         {
17             StringBuilder sb = new StringBuilder();
18 
19             for (int i = 0; i < count; i++)
20             {
21                 sb.Append(_testStr);
22             }
23 
24             return sb.ToString();
25         }
26         public string UseStringBuilderWithCapacity(int count)
27         {
28             StringBuilder sb = new StringBuilder(count * _testStr.Length);
29 
30             for (int i = 0; i < count; i++)
31             {
32                 sb.Append(_testStr);
33             }
34 
35             return sb.ToString();
36         }
37         public string UseStringConcat(int count)
38         {
39             string[] list = new string[count];
40             for (int i = 0; i < count; i++)
41             {
42                 list[i] = _testStr;
43             }
44             return string.Concat(list);
45         }
46         public string UseStringConcatWithList(int count)
47         {
48             List<string> list = new List<string>(count);
49             for (int i = 0; i < count; i++)
50             {
51                 list.Add(_testStr);
52             }
53             return string.Concat(list);
54         }
55         public string UseStringConcatWithListToArray(int count)
56         {
57             List<string> list = new List<string>(count);
58             for (int i = 0; i < count; i++)
59             {
60                 list.Add(_testStr);
61             }
62             return string.Concat(list.ToArray());
63         }
64     }

 1 Stopwatch watch = new Stopwatch();
 2             StringSpeedTest strSpeedTest = new StringSpeedTest();
 3 
 4             int count = 10000;
 5             TimeSpan time = new TimeSpan(0, 0, 0);
 6             watch.Start();
 7             for (int i = 0; i < 10; i++)
 8             {
 9                 Console.WriteLine("-------------------------------------------------------------------");
10                 strSpeedTest.StringAdd(count);
11 
12                 Console.WriteLine($"StringAdd:\t\t\t{watch.Elapsed - time}");
13                 time = watch.Elapsed;
14 
15                 strSpeedTest.UseStringBuilder(count);
16                 Console.WriteLine($"UseStringBuilder:\t\t{watch.Elapsed - time}");
17                 time = watch.Elapsed;
18 
19                 strSpeedTest.UseStringBuilderWithCapacity(count);
20                 Console.WriteLine($"UseStringBuilderWithCapacity:\t{watch.Elapsed - time}");
21                 time = watch.Elapsed;
22 
23                 strSpeedTest.UseStringConcatWithList(count);
24                 Console.WriteLine($"UseStringConcatWithList:\t{watch.Elapsed - time}");
25                 time = watch.Elapsed;
26 
27                 strSpeedTest.UseStringConcatWithListToArray(count);
28                 Console.WriteLine($"UseStringConcatWithListToArray:\t{watch.Elapsed - time}");
29                 time = watch.Elapsed;
30 
31                 strSpeedTest.UseStringConcat(count);
32                 Console.WriteLine($"UseStringConcat:\t\t{watch.Elapsed - time}");
33 
34 
35                 Console.WriteLine("*******************************************************************");
36             }
37 
38             watch.Stop();

测试结果：

 1 -------------------------------------------------------------------
 2 StringAdd:                      00:00:00.2908582
 3 UseStringBuilder:               00:00:00.0008419
 4 UseStringBuilderWithCapacity:   00:00:00.0008429
 5 UseStringConcatWithList:        00:00:00.0101701
 6 UseStringConcatWithListToArray: 00:00:00.0032169
 7 UseStringConcat:                00:00:00.0005971
 8 *******************************************************************
 9 -------------------------------------------------------------------
10 StringAdd:                      00:00:00.1373059
11 UseStringBuilder:               00:00:00.0003654
12 UseStringBuilderWithCapacity:   00:00:00.0003533
13 UseStringConcatWithList:        00:00:00.0006684
14 UseStringConcatWithListToArray: 00:00:00.0003922
15 UseStringConcat:                00:00:00.0003371
16 *******************************************************************
17 -------------------------------------------------------------------
18 StringAdd:                      00:00:00.1313924
19 UseStringBuilder:               00:00:00.0003778
20 UseStringBuilderWithCapacity:   00:00:00.0010882
21 UseStringConcatWithList:        00:00:00.0010397
22 UseStringConcatWithListToArray: 00:00:00.0007571
23 UseStringConcat:                00:00:00.0004528
24 *******************************************************************
25 -------------------------------------------------------------------
26 StringAdd:                      00:00:00.1282163
27 UseStringBuilder:               00:00:00.0003770
28 UseStringBuilderWithCapacity:   00:00:00.0003452
29 UseStringConcatWithList:        00:00:00.0006388
30 UseStringConcatWithListToArray: 00:00:00.0003873
31 UseStringConcat:                00:00:00.0004068
32 *******************************************************************
33 -------------------------------------------------------------------
34 StringAdd:                      00:00:00.1349978
35 UseStringBuilder:               00:00:00.0004084
36 UseStringBuilderWithCapacity:   00:00:00.0003698
37 UseStringConcatWithList:        00:00:00.0006802
38 UseStringConcatWithListToArray: 00:00:00.0004059
39 UseStringConcat:                00:00:00.0003503
40 *******************************************************************
41 -------------------------------------------------------------------
42 StringAdd:                      00:00:00.1290642
43 UseStringBuilder:               00:00:00.0003813
44 UseStringBuilderWithCapacity:   00:00:00.0003674
45 UseStringConcatWithList:        00:00:00.0006886
46 UseStringConcatWithListToArray: 00:00:00.0004115
47 UseStringConcat:                00:00:00.0003509
48 *******************************************************************
49 -------------------------------------------------------------------
50 StringAdd:                      00:00:00.1363654
51 UseStringBuilder:               00:00:00.0003885
52 UseStringBuilderWithCapacity:   00:00:00.0004270
53 UseStringConcatWithList:        00:00:00.0007209
54 UseStringConcatWithListToArray: 00:00:00.0004618
55 UseStringConcat:                00:00:00.0003863
56 *******************************************************************
57 -------------------------------------------------------------------
58 StringAdd:                      00:00:00.1326732
59 UseStringBuilder:               00:00:00.0003978
60 UseStringBuilderWithCapacity:   00:00:00.0003965
61 UseStringConcatWithList:        00:00:00.0006867
62 UseStringConcatWithListToArray: 00:00:00.0004012
63 UseStringConcat:                00:00:00.0003480
64 *******************************************************************
65 -------------------------------------------------------------------
66 StringAdd:                      00:00:00.1275684
67 UseStringBuilder:               00:00:00.0003673
68 UseStringBuilderWithCapacity:   00:00:00.0004190
69 UseStringConcatWithList:        00:00:00.0007201
70 UseStringConcatWithListToArray: 00:00:00.0004572
71 UseStringConcat:                00:00:00.0003848
72 *******************************************************************
73 -------------------------------------------------------------------
74 StringAdd:                      00:00:00.1606576
75 UseStringBuilder:               00:00:00.0004435
76 UseStringBuilderWithCapacity:   00:00:00.0005415
77 UseStringConcatWithList:        00:00:00.0007263
78 UseStringConcatWithListToArray: 00:00:00.0004205
79 UseStringConcat:                00:00:00.0003707
80 *******************************************************************

 从结果中可以看到，StringBuilder 速度不是永远最快的。当把cout调整为100000时 结果如下，由于string直接+速度太慢直接去除比较梯队。

 1 -------------------------------------------------------------------
 2 UseStringBuilder:               00:00:00.1400624
 3 UseStringBuilderWithCapacity:   00:00:00.0057860
 4 UseStringConcatWithList:        00:00:00.0186478
 5 UseStringConcatWithListToArray: 00:00:00.0074943
 6 UseStringConcat:                00:00:00.0054871
 7 *******************************************************************
 8 -------------------------------------------------------------------
 9 UseStringBuilder:               00:00:00.0115386
10 UseStringBuilderWithCapacity:   00:00:00.0057336
11 UseStringConcatWithList:        00:00:00.0080408
12 UseStringConcatWithListToArray: 00:00:00.0052401
13 UseStringConcat:                00:00:00.0037864
14 *******************************************************************
15 -------------------------------------------------------------------
16 UseStringBuilder:               00:00:00.0085633
17 UseStringBuilderWithCapacity:   00:00:00.0049141
18 UseStringConcatWithList:        00:00:00.0179742
19 UseStringConcatWithListToArray: 00:00:00.0045335
20 UseStringConcat:                00:00:00.0042053
21 *******************************************************************
22 -------------------------------------------------------------------
23 UseStringBuilder:               00:00:00.0085083
24 UseStringBuilderWithCapacity:   00:00:00.0041245
25 UseStringConcatWithList:        00:00:00.0080081
26 UseStringConcatWithListToArray: 00:00:00.0043282
27 UseStringConcat:                00:00:00.0037264
28 *******************************************************************
29 -------------------------------------------------------------------
30 UseStringBuilder:               00:00:00.0087733
31 UseStringBuilderWithCapacity:   00:00:00.0086311
32 UseStringConcatWithList:        00:00:00.0080520
33 UseStringConcatWithListToArray: 00:00:00.0056323
34 UseStringConcat:                00:00:00.0038094
35 *******************************************************************
36 -------------------------------------------------------------------
37 UseStringBuilder:               00:00:00.0086884
38 UseStringBuilderWithCapacity:   00:00:00.0063233
39 UseStringConcatWithList:        00:00:00.0081824
40 UseStringConcatWithListToArray: 00:00:00.0055393
41 UseStringConcat:                00:00:00.0040967
42 *******************************************************************
43 -------------------------------------------------------------------
44 UseStringBuilder:               00:00:00.0108527
45 UseStringBuilderWithCapacity:   00:00:00.0048482
46 UseStringConcatWithList:        00:00:00.0079176
47 UseStringConcatWithListToArray: 00:00:00.0043536
48 UseStringConcat:                00:00:00.0042921
49 *******************************************************************
50 -------------------------------------------------------------------
51 UseStringBuilder:               00:00:00.0119569
52 UseStringBuilderWithCapacity:   00:00:00.0043067
53 UseStringConcatWithList:        00:00:00.0091552
54 UseStringConcatWithListToArray: 00:00:00.0045956
55 UseStringConcat:                00:00:00.0041058
56 *******************************************************************
57 -------------------------------------------------------------------
58 UseStringBuilder:               00:00:00.0096342
59 UseStringBuilderWithCapacity:   00:00:00.0055840
60 UseStringConcatWithList:        00:00:00.0073000
61 UseStringConcatWithListToArray: 00:00:00.0056438
62 UseStringConcat:                00:00:00.0038800
63 *******************************************************************
64 -------------------------------------------------------------------
65 UseStringBuilder:               00:00:00.0090576
66 UseStringBuilderWithCapacity:   00:00:00.0047266
67 UseStringConcatWithList:        00:00:00.0076383
68 UseStringConcatWithListToArray: 00:00:00.0048706
69 UseStringConcat:                00:00:00.0048964
70 *******************************************************************

 从结果中可以看到再没有使用初始化StringBuilder 容器容量的时候，性能与使用string.Concat相差已经很大。在使用初始化容量之后 性能有较大的提升。

总结如下：

1、在只知道字符串最终长度的时候，可以使用 StringBuilder 并初始化容量，可以有较大的提升；

2、在不知道最终字符串长度时候，但是知道拼接字符串次数的时候，可以将每次字符串保存在一个字符串数组中，可以有较大的性能提升;

3、在不知道字符串长度以及拼接的次数的时候，可以使用LIst<string>  保存，可以有较大的性能提升。当然也可以大约估计最终字符串长度，然后初始化StringBuilder 时候使用较大的容量，以空间来换取速度

当然这些都是在拼接字符串的次数很大的情况下，会有较大的性能提升。

参考：

http://blog.zhaojie.me/2009/11/string-concat-perf-1-benchmark.html