今天我们来介绍一下C#语言的字符串花式拼接方式

1. 基本使用

废话少说，我们直接上代码，介绍一下字符串的拼接的方式

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace CSharpPrimeNumber
{public class StringSplicingDemo{public void RunDemo(){Console.WriteLine("---------------------------------基本使用---------------------------------");Console.WriteLine("PlusSignString:" + PlusSignString("小蔡同学", "非常帅"));Console.WriteLine("StringFormatString:" + StringFormatString("小蔡同学", "非常帅"));Console.WriteLine("StringBuilderString:" + StringBuilderString("小蔡同学", "非常帅"));Console.WriteLine("StringFormatVS2017:" + StringFormatVS2017("小蔡同学", "非常帅"));Console.WriteLine("--------------------------------------------------------------------------");}/// <summary>/// +号运算/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string PlusSignString(string str1,string str2){string strReturn = str1 + str2;return strReturn;}/// <summary>/// stringFormat拼接字符串/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string StringFormatString(string str1, string str2){string strReturn = string.Format("{0}{1}",str1,str2);return strReturn;}/// <summary>/// StringBuilder拼接字符串/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string StringBuilderString(string str1, string str2){StringBuilder stringBuilder = new StringBuilder();stringBuilder.Append(str1);stringBuilder.Append(str2);return stringBuilder.ToString();}/// <summary>/// VS2017以上提供的字符串拼接/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string StringFormatVS2017(string str1, string str2){string strReturn = string.Format($"{str1}{str2}");return strReturn;}}static void Main(string[] args){StringSplicingDemo pStringSplicingDemo = new StringSplicingDemo();pStringSplicingDemo.RunDemo();Console.ReadKey();}}

好了，到这里，今天的博客就水到这里了

哈哈哈，各位看客老爷别走，还没有分析完。我们继续说一下以上这几种方式的适用场景。

2. 具体分析

2.1. 算法效率

我们建立几个测试数据，我们将他们拼接，看看效率差距有多大

• 简单拼接n次，将str1="小菜同学"和str2="非常帅",进行一定次数的拼接
• 复杂拼接n次，将滕王阁序节选拆分后拼接，进行一定次数的拼接

先看结果

---------------------------------1.基本使用---------------------------------
PlusSignString:小蔡同学非常帅
StringFormatString:小蔡同学非常帅
StringBuilderString:小蔡同学非常帅
StringFormatVS2017:小蔡同学非常帅
--------------------------------------------------------------------------
---------------------------------2.算法效率---------------------------------
---------------------------------2.1.简单拼接---------------------------------
---------------------------------2.1.1.简单拼接10000次---------------------------------
PlusSignString:计算10000总共花费1.5047 ms.
StringFormatString:计算10000总共花费3.3441 ms.
StringBuilderString:计算10000总共花费2.7871 ms.
SingletonStringBuilderString:计算10000总共花费2.6882 ms.
StringFormatVS2017:计算10000总共花费1.5376 ms.
--------------------------------------------------------------------------
---------------------------------2.1.2.简单拼接100000次---------------------------------
PlusSignString:计算100000总共花费10.0948 ms.
StringFormatString:计算100000总共花费34.3649 ms.
StringBuilderString:计算100000总共花费16.5996 ms.
SingletonStringBuilderString:计算100000总共花费17.6449 ms.
StringFormatVS2017:计算100000总共花费62.0455 ms.
---------------------------------2.1.2.简单拼接100000次---------------------------------
PlusSignString:计算1000000总共花费117.9943 ms.
StringFormatString:计算1000000总共花费216.8216 ms.
StringBuilderString:计算1000000总共花费170.7078 ms.
SingletonStringBuilderString:计算1000000总共花费103.9131 ms.
StringFormatVS2017:计算1000000总共花费226.8915 ms.
--------------------------------------------------------------------------
--------------------------------------------------------------------------
---------------------------------2.2.复杂拼接---------------------------------
---------------------------------2.2.1.复杂拼接10000次---------------------------------
披绣闼,俯雕甍,山原旷其盈视,川泽纡其骇瞩,闾阎扑地,钟鸣鼎食之家,舸舰弥津,青雀黄龙之舳,云销雨霁,彩彻区明,落霞与孤鹜齐飞,秋水共长天一色,渔舟唱晚,响穷彭蠡之滨,雁阵惊寒,声断衡阳之浦,遥襟甫畅,逸兴遄飞,爽籁发而清风生,纤歌凝而白云遏,睢园绿竹,气凌彭泽之樽,邺水朱华,光照临川之笔,四美具,二难并,穷睇眄于中天,极娱游于暇日,天高地迥,觉宇宙之无穷,兴尽悲来,识盈虚之有数,望长安于日下,目吴会于云间,地势极而南溟深,天柱高而北辰远,关山难越,谁悲失路之人,萍水相逢,尽是他乡之客,怀帝阍而不见,奉宣室以 何年,嗟乎,时运不齐,命途多舛,冯唐易老,李广难封,屈贾谊于长沙,非无圣主,窜梁鸿于海曲,岂乏明时,所赖君子见机,达人知命,老当益壮,宁移白首之心,穷且益坚,不坠青云之志,酌贪泉而觉爽,处涸辙以犹欢,北海虽赊,扶摇可接,东隅已逝,桑榆非晚,孟尝高洁,空余报国之情,阮籍猖狂,岂效穷途之哭。
PlusSignString:计算10000总共花费107.0751 ms.
StringFormatString:计算10000总共花费211.6322 ms.
StringBuilderString:计算10000总共花费24.7743 ms.
SingletonStringBuilderString:计算10000总共花费13.1791 ms.
StringFormatVS2017:计算10000总共花费667.0529 ms.
--------------------------------------------------------------------------
---------------------------------2.2.2.复杂拼接100000次---------------------------------
PlusSignString:计算100000总共花费708.8968 ms.
StringFormatString:计算100000总共花费1498.7978 ms.
StringBuilderString:计算100000总共花费181.1703 ms.
SingletonStringBuilderString:计算100000总共花费103.6469 ms.
StringFormatVS2017:计算100000总共花费4302.9795 ms.
--------------------------------------------------------------------------

其次结论

• 当简单拼接时，+的方式是最优的
• 当复杂拼接时，StringBuilder的方式最优
• 至于string.Format代码的可读性和维护性高一些

再说原因

• 简单拼接时，StringBuilder生成实例的方式不划算，且需要对对象进行一定操作清理，如使用SingletonStringBuilderString单例StringBuilder
• 复杂拼接时，则是由于string类型具有不可变性，在底层的存储方式是采用享元的方式存储的，对string字符串的操作（如拼接、Trim()等）都会在内存中产生一个新的字符串对象，在对字符串进行频繁修改的情况下，如在For循环中进行操作等，那么将会频繁的创建新的字符串对象，造成系统的不必要开销，所以这种情况下大家都推荐使用StringBuilder类来对字符串进行操作，那么到底是怎么实现的呢？可以参见下方代码

    /// <summary>/// Appends a string to the end of this builder./// </summary>/// <param name="value">The string to append.</param>public StringBuilder Append(string? value){if (value != null){// We could have just called AppendHelper here; this is a hand-specialization of that code.char[] chunkChars = m_ChunkChars;int chunkLength = m_ChunkLength;int valueLen = value.Length;if (((uint)chunkLength + (uint)valueLen) < (uint)chunkChars.Length) // Use strictly < to avoid issues if count == 0, newIndex == length{if (valueLen <= 2){if (valueLen > 0){chunkChars[chunkLength] = value[0];}if (valueLen > 1){chunkChars[chunkLength + 1] = value[1];}}else{Buffer.Memmove(ref Unsafe.Add(ref MemoryMarshal.GetArrayDataReference(chunkChars), chunkLength),ref value.GetRawStringData(),(nuint)valueLen);}m_ChunkLength = chunkLength + valueLen;}else{AppendHelper(value);}}return this;}

最后贴代码

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace CSharpPrimeNumber
{public class StringSplicingDemo{public void RunDemo(){Console.WriteLine("---------------------------------1.基本使用---------------------------------");Console.WriteLine("PlusSignString:" + PlusSignString("小蔡同学", "非常帅"));Console.WriteLine("StringFormatString:" + StringFormatString("小蔡同学", "非常帅"));Console.WriteLine("StringBuilderString:" + StringBuilderString("小蔡同学", "非常帅"));Console.WriteLine("StringFormatVS2017:" + StringFormatVS2017("小蔡同学", "非常帅"));Console.WriteLine("--------------------------------------------------------------------------");Console.WriteLine("---------------------------------2.算法效率---------------------------------");Console.WriteLine("---------------------------------2.1.简单拼接---------------------------------");Console.WriteLine("---------------------------------2.1.1.简单拼接10000次---------------------------------");SimpleTogether(10000, PlusSignString);SimpleTogether(10000, StringFormatString);SimpleTogether(10000, StringBuilderString);SimpleTogether(10000, SingletonStringBuilderString);SimpleTogether(10000, StringFormatVS2017);Console.WriteLine("--------------------------------------------------------------------------");Console.WriteLine("---------------------------------2.1.2.简单拼接100000次---------------------------------");SimpleTogether(100000, PlusSignString);SimpleTogether(100000, StringFormatString);SimpleTogether(100000, StringBuilderString);SimpleTogether(100000, SingletonStringBuilderString);SimpleTogether(100000, StringFormatVS2017);Console.WriteLine("---------------------------------2.1.2.简单拼接100000次---------------------------------");SimpleTogether(1000000, PlusSignString);SimpleTogether(1000000, StringFormatString);SimpleTogether(1000000, StringBuilderString);SimpleTogether(1000000, SingletonStringBuilderString);SimpleTogether(1000000, StringFormatVS2017);Console.WriteLine("--------------------------------------------------------------------------");Console.WriteLine("--------------------------------------------------------------------------");Console.WriteLine("---------------------------------2.2.复杂拼接---------------------------------");Console.WriteLine("---------------------------------2.2.1.复杂拼接10000次---------------------------------");List<string> listInfo = new List<string>() {"披绣闼","俯雕甍","山原旷其盈视","川泽纡其骇瞩","闾阎扑地","钟鸣鼎食之家","舸舰弥津","青雀黄龙之舳","云销雨霁","彩彻区明","落霞与孤鹜齐飞","秋水共长天一色","渔舟唱晚","响穷彭蠡之滨","雁阵惊寒","声断衡阳之浦","遥襟甫畅","逸兴遄飞","爽籁发而清风生","纤歌凝而白云遏","睢园绿竹","气凌彭泽之樽","邺水朱华","光照临川之笔","四美具","二难并","穷睇眄于中天","极娱游于暇日","天高地迥","觉宇宙之无穷","兴尽悲来","识盈虚之有数","望长安于日下","目吴会于云间","地势极而南溟深","天柱高而北辰远","关山难越","谁悲失路之人","萍水相逢","尽是他乡之客","怀帝阍而不见","奉宣室以何年","嗟乎","时运不齐","命途多舛","冯唐易老","李广难封","屈贾谊于长沙","非无圣主","窜梁鸿于海曲","岂乏明时","所赖君子见机","达人知命","老当益壮","宁移白首之心","穷且益坚","不坠青云之志","酌贪泉而觉爽","处涸辙以犹欢","北海虽赊","扶摇可接","东隅已逝","桑榆非晚","孟尝高洁","空余报国之情","阮籍猖狂","岂效穷途之哭" };Console.WriteLine(string.Join(",", listInfo) + "。");ComplexTogether(10000, listInfo, PlusSignString);ComplexTogether(10000,listInfo, StringFormatString); ComplexTogether(10000, listInfo, StringBuilderString);ComplexTogether(10000, listInfo, SingletonStringBuilderString);ComplexTogether(10000, listInfo, StringFormatVS2017);Console.WriteLine("--------------------------------------------------------------------------");Console.WriteLine("---------------------------------2.2.2.复杂拼接100000次---------------------------------");ComplexTogether(100000,listInfo, PlusSignString);ComplexTogether(100000,listInfo, StringFormatString);ComplexTogether(100000,listInfo, StringBuilderString);ComplexTogether(100000, listInfo, SingletonStringBuilderString);ComplexTogether(100000, listInfo, StringFormatVS2017);Console.WriteLine("--------------------------------------------------------------------------");}StringBuilder SingletonStringBuilder = new StringBuilder();#region 复杂字符串拼接代码段/// <summary>/// 复杂字符串拼接/// </summary>/// <param name="num"></param>/// <param name="list"></param>/// <param name="action"></param>public void ComplexTogether(int num, List<string> list, Func<List<string>, string> action){Stopwatch sw = new Stopwatch();sw.Start();for (int i = 0; i < num; i++){action(list);}sw.Stop();TimeSpan ts2 = sw.Elapsed;Console.WriteLine($"{action.Method.Name}:计算{num}总共花费{ts2.TotalMilliseconds} ms.");}public string PlusSignString(List<string> listInfo){string strReturn = "";for (int i = 0; i < listInfo.Count; i++){strReturn += listInfo[i];}return strReturn;}public string StringFormatString(List<string> listInfo){string strReturn = "";for (int i = 0; i < listInfo.Count; i++){strReturn =string.Format("{0}{1}",strReturn,listInfo[i]);}return strReturn;}public string StringBuilderString(List<string> listInfo){StringBuilder stringBuilder = new StringBuilder();foreach (var item in listInfo){stringBuilder.Append(item);}return stringBuilder.ToString();}/// <summary>/// StringBuilder拼接字符串/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string SingletonStringBuilderString(List<string> listInfo){SingletonStringBuilder.Clear();foreach (var item in listInfo){SingletonStringBuilder.Append(item);}return SingletonStringBuilder.ToString();}public string StringFormatVS2017(List<string> listInfo){string strReturn = "";for (int i = 0; i < listInfo.Count; i++){strReturn = string.Format($"{strReturn}{listInfo[i]}");}return strReturn;}#endregion#region 简单字符串拼接代码段/// <summary>/// 简单字符串拼接/// </summary>/// <param name="num"></param>/// <param name="action"></param>public void SimpleTogether(int num, Func<string,string, string> action){Stopwatch sw = new Stopwatch();sw.Start();for (int i = 0; i < num; i++){action("小蔡同学", "非常帅"+i);}sw.Stop();TimeSpan ts2 = sw.Elapsed;Console.WriteLine($"{action.Method.Name}:计算{num}总共花费{ts2.TotalMilliseconds} ms.");}/// <summary>/// +号运算/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string PlusSignString(string str1,string str2){string strReturn = str1 + str2;return strReturn;}/// <summary>/// stringFormat拼接字符串/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string StringFormatString(string str1, string str2){string strReturn = string.Format("{0}{1}",str1,str2);return strReturn;}/// <summary>/// StringBuilder拼接字符串/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string SingletonStringBuilderString(string str1, string str2){SingletonStringBuilder.Clear();SingletonStringBuilder.Append(str1);SingletonStringBuilder.Append(str2);return SingletonStringBuilder.ToString();}/// <summary>/// StringBuilder拼接字符串/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string StringBuilderString(string str1, string str2){StringBuilder stringBuilder = new StringBuilder();stringBuilder.Append(str1);stringBuilder.Append(str2);return stringBuilder.ToString();}/// <summary>/// VS2017以上提供的字符串拼接/// </summary>/// <param name="str1"></param>/// <param name="str2"></param>/// <returns></returns>public string StringFormatVS2017(string str1, string str2){string strReturn = string.Format($"{str1}{str2}");return strReturn;}#endregion}
}

2.2 代码可读性

1. 简单情况下+运算,是最清晰的
2. 极度复杂且重复的情况下StringBuilder是最佳的方式
3. 当只是拼接一次长字符串是,我认为string.format可读性是最强的

• string.Format("{0}",str) 和 string.Format($"{str}")

  • string.Format($"{str}") 我非常推崇这种写法

举例说明：现在有一个如下代码，使用string.Format("{0}",str)

string strUpdateSql=string.Format("update {0} set FieldA='{1}' where ID ={2}",TableName,FieldAValuem,IDValue);

以上代码是拼接一个sql语句，这样相较+和StringBuilder更加具有优势。

如果这个strUpdateSql不发生改变就还好，但是如果发生改变，如现在需要多更新几个字段，代码转变为如下：几种情况

string strUpdateSql=string.Format("update {0} set FieldA='{1}',FieldA='{2}' where ID ={3}",TableName,FieldAValuem,FieldBValuem,IDValue);

string strUpdateSql=string.Format("update {0} set FieldA='{1}',FieldA='{3}' where ID ={2}",TableName,FieldAValuem,IDValue,FieldBValuem);

如果仔细思考的话，我们应该想到：当字段复杂的时候上述两种拼接都是一个毫无必要的拼接，第一种情况:遵循强迫症或者说为了代码有一个从始至终的编码逻辑，就需要调整，第二种情况：可以预想到当经过几轮的没有原则的修改，这个长代码的维护性及其的差

一下我们贴一下+的代码,仔细对比一下，个人认为在代码的引号上非常容易出错

string strUpdateSql="update "+TableName+" set FieldA='"+FieldAValuem+"',FieldA='"+FieldBValuem+"' where ID ="+IDValue;

在这里我们写一下string.Format($"{str}")

string strUpdateSql=string.Format($"update {TableName} set FieldA='{FieldAValuem}',FieldA='{FieldBValuem}' where ID ={IDValue}");

以上代码的可读性以及维护性及其的好。

但是，凡是都担心但是，这种写法是在VS2017之后出现的，这种写法是编译器行为，如果需要在低版本VS中继续编写代码时，就不建议使用这种代码编写格式了。

3. 小技巧

我个人还是看了蛮多上古代码的,其中有一种代码我见过很多，现在有三个人名，需要用、分隔拼接起来，大部分代码如下方式。

List<string> listName=new List<string>(){"张三","李四","王五"};string strReturn=listName[0];for(int i=1;i<listName.Count;i++)
{strReturn+="、"+listName[0];
}// string strReturn="";
// for(int i=0;i<listName.Count;i++)
// {
//     strReturn+="、"+listName[0];
// }
// strRetuern=strReturn==""?strReturn:strReturn.SubString(1);return strReturn;

个人的写法如下：

List<string> listName=new List<string>(){"张三","李四","王五"};string strReturn=string.Join("、",listName);

C#源码如下：mscorlib_Source\System\String.cs

[ComVisible(false)]
public static string Join(string separator, IEnumerable<string> values)
{if (values == null){throw new ArgumentNullException("values");}if (separator == null){separator = Empty;}using (IEnumerator<string> enumerator = values.GetEnumerator()){if (!enumerator.MoveNext()){return Empty;}StringBuilder builder = new StringBuilder();if (enumerator.Current != null){builder.Append(enumerator.Current);}while (enumerator.MoveNext()){builder.Append(separator);if (enumerator.Current != null){builder.Append(enumerator.Current);}}return builder.ToString();}
}

我个人写代码和改代码都相较蛮快的，是因为在每一个细节上都考虑可读性、简洁、是不是常人思路以及这个地方如果改怎么方便改