StringBuilder 对比 String / Fast String Operations with .NET 2.0

StringBuilder vs. String / Fast String Operations with .NET 2.0

// Used Test functions for this chart string StringRemove(string str, int Count) { for(int i=0;i<Count;i++) str = str.Remove(0, 1); return str; } string StringBuilderRemove(string str, int Count) { StringBuilder sb = new StringBuilder(str); for(int i=0;i<Count;i++) sb.Remove(0, 1); return sb.ToString(); } string StringInsert(string str, string [] inserts) { foreach (string insert in inserts) str = str.Insert(0, insert); return str; } string StringBuilderInsert(string str, string [] inserts) { StringBuilder sb = new StringBuilder(str); foreach (string insert in inserts) sb.Insert(0, insert); return sb.ToString(); } // Used Test functions for this chart string StringReplace(string str, List<KeyValuePair<string,string>> searchReplace) { foreach (KeyValuePair<string, string> sreplace in searchReplace) str = str.Replace(sreplace.Key, sreplace.Value); return str; } string StringBuilderReplace(string str, List<KeyValuePair<string,string>> searchReplace) { StringBuilder sb = new StringBuilder(str); foreach (KeyValuePair<string, string> sreplace in searchReplace) sb.Replace(sreplace.Key, sreplace.Value); return sb.ToString(); } // Functions used for this chart string StringFormat(string format, int Count, params object[] para) { string str=String.Empty; for(int i=0;i<Count;i++) str += String.Format(format,para); return str; } string StringBuilderFormat(string format, int Count, params object[] para ) { StringBuilder sb = new StringBuilder(); for(int i=0;i<Count;i++) sb.AppendFormat(format, para); return sb.ToString(); } string Add(params string[] strings) // Used Test functions for this chart { string ret = String.Empty; foreach (string str in strings) ret += str; return ret; } string Concat(params string[] strings) { return String.Concat(strings); } string StringBuilderAppend(params string[] strings) { StringBuilder sb = new StringBuilder(); foreach (string str in strings) sb.Append(str); return sb.ToString(); } string Join(params string[] strings) { return String.Join(String.Empty, strings); } // Used Test functions for this chart int StringCompare(string str1, string str2) { return String.Compare(str1, str2, StringComparison.InvariantCulture); } int StringCompareOrdinal(string str1, string str2) { return String.CompareOrdinal(str1, str2); }

 

Conclusions

The following recommendations are valid for our small test strings (~30 chars) but should be applicable to bigger strings (100-500) as well (measure for yourself!). I have seen many synthetic performance measurements that demonstrate the power of StringBuilder with strings that are 10KB and bigger. This is the 1% case in real world programs. Most strings will be significantly shorter. When you optimize a function and you can "feel" the construction costs of an additional object then you have to look very carefully if you can afford the additional initialization costs of StringBuilder.

 

String Operation	Most Efficient
Insert	StringBuilder.Insert > 2 Insertion Strings String.Insert otherwise
Remove	StringBuilder is faster > 2 characters to remove
Replace	String.Replace always
Format	String.Format < 5 Append + Format operations StringBuilder.AppendFormat > 5 calls
Concatenation	+ for 2 strings String.Join > 2 strings to concatenate

 

The shiny performance saving StringBuilder does not help in all cases and is, in some cases, slower than other functions. When you want to have good string concatenation performance I recommend strongly that you use String .Join which does an incredible job.