C# 字符串拼接性能探索 c#中+、string.Concat、string.Format、StringBuilder.Append四种方式进行字符串拼接时的性能
本文通过ANTS Memory Profiler工具探索c#中+、string.Concat、string.Format、StringBuilder.Append四种方式进行字符串拼接时的性能。
本文涉及程序为.NET Core 2.0控制台应用程序。
一、常量字符串拼接
private static void TestPerformance(Action action, int times)
{
Stopwatch sw = new Stopwatch();
sw.Start();
for(int i = 0; i < times; i++)
{
action();
}
sw.Stop();
Console.WriteLine(action.Method.Name + ", FullTime: " + sw.ElapsedMilliseconds);
}
1.+方法
1.1连续拼接
private static void AddTest()
{
string s = string.Empty;
s = "1" + "2" + "3" + "4" + "5" + "6" + "7" + "8";
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void AddTest() cil managed
{
// Code size 7 (0x7)
.maxstack 8
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: pop
IL_0006: ret
} // end of method Program::AddTest
1.2分段拼接
private static void AddWithParamTest2()
{
string s = string.Empty;
s += "1";
s += "2";
s += "3";
s += "4";
s += "5";
s += "6";
s += "7";
s += "8";
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void AddWithParamTest2() cil managed
{
// Code size 87 (0x57)
.maxstack 2
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: ldstr "1"
IL_000a: call string [System.Runtime]System.String::Concat(string,
string)
IL_000f: ldstr "2"
IL_0014: call string [System.Runtime]System.String::Concat(string,
string)
IL_0019: ldstr "3"
IL_001e: call string [System.Runtime]System.String::Concat(string,
string)
IL_0023: ldstr "4"
IL_0028: call string [System.Runtime]System.String::Concat(string,
string)
IL_002d: ldstr "5"
IL_0032: call string [System.Runtime]System.String::Concat(string,
string)
IL_0037: ldstr "6"
IL_003c: call string [System.Runtime]System.String::Concat(string,
string)
IL_0041: ldstr "7"
IL_0046: call string [System.Runtime]System.String::Concat(string,
string)
IL_004b: ldstr "8"
IL_0050: call string [System.Runtime]System.String::Concat(string,
string)
IL_0055: pop
IL_0056: ret
} // end of method Program::AddWithParamTest2
通过IL代码可以看出，分段的+=代码调用的是Concat方法，并且比连续的+多开辟了许多内存空间。
2.Concat方法
2.1分次Concat
private static void ConcatTest()
{
string s = string.Empty;
s = string.Concat(s, "1");
s = string.Concat(s, "2");
s = string.Concat(s, "3");
s = string.Concat(s, "4");
s = string.Concat(s, "5");
s = string.Concat(s, "6");
s = string.Concat(s, "7");
s = string.Concat(s, "8");
}
IL代码：
.method private hidebysig static void AddWithParamTest2() cil managed
{
// Code size 87 (0x57)
.maxstack 2
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: ldstr "1"
IL_000a: call string [System.Runtime]System.String::Concat(string,
string)
IL_000f: ldstr "2"
IL_0014: call string [System.Runtime]System.String::Concat(string,
string)
IL_0019: ldstr "3"
IL_001e: call string [System.Runtime]System.String::Concat(string,
string)
IL_0023: ldstr "4"
IL_0028: call string [System.Runtime]System.String::Concat(string,
string)
IL_002d: ldstr "5"
IL_0032: call string [System.Runtime]System.String::Concat(string,
string)
IL_0037: ldstr "6"
IL_003c: call string [System.Runtime]System.String::Concat(string,
string)
IL_0041: ldstr "7"
IL_0046: call string [System.Runtime]System.String::Concat(string,
string)
IL_004b: ldstr "8"
IL_0050: call string [System.Runtime]System.String::Concat(string,
string)
IL_0055: pop
IL_0056: ret
} // end of method Program::AddWithParamTest2
可见IL代码与+分段拼接常量字符串相同，性能相似。
2.2Concat一次拼接常量字符串
private static void ConcatTest2()
{
string s = string.Empty;
string.Concat(s, "1", "2", "3", "4", "5", "6", "7", "8");
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void ConcatTest2() cil managed
{
// Code size 88 (0x58)
.maxstack 4
.locals init (string V_0)
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: stloc.0
IL_0006: ldc.i4.s 9
IL_0008: newarr [System.Runtime]System.String
IL_000d: dup
IL_000e: ldc.i4.0
IL_000f: ldloc.0
IL_0010: stelem.ref
IL_0011: dup
IL_0012: ldc.i4.1
IL_0013: ldstr "1"
IL_0018: stelem.ref
IL_0019: dup
IL_001a: ldc.i4.2
IL_001b: ldstr "2"
IL_0020: stelem.ref
IL_0021: dup
IL_0022: ldc.i4.3
IL_0023: ldstr "3"
IL_0028: stelem.ref
IL_0029: dup
IL_002a: ldc.i4.4
IL_002b: ldstr "4"
IL_0030: stelem.ref
IL_0031: dup
IL_0032: ldc.i4.5
IL_0033: ldstr "5"
IL_0038: stelem.ref
IL_0039: dup
IL_003a: ldc.i4.6
IL_003b: ldstr "6"
IL_0040: stelem.ref
IL_0041: dup
IL_0042: ldc.i4.7
IL_0043: ldstr "7"
IL_0048: stelem.ref
IL_0049: dup
IL_004a: ldc.i4.8
IL_004b: ldstr "8"
IL_0050: stelem.ref
IL_0051: call string [System.Runtime]System.String::Concat(string[]) IL_0056: stloc.0 IL_0057: ret
} // end of method Program::ConcatTest2
通过IL代码可以看出，string.Concat(s, s1, s2, s3)并不调用String.Concat方法，而是直接在堆栈上进行操作。因为需要局部变量来标记，比分次调用Concat方法所占的内存要多一些。
3.Format方法
3.1一次Format
private static void FormatTest()
{
string s = string.Empty;
s = string.Format("{0}{1}{2}{3}{4}{5}{6}{7}", "1", "2", "3", "4", "5", "6", "7", "8");
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void FormatTest() cil managed
{
// Code size 88 (0x58)
.maxstack 5
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: pop
IL_0006: ldstr "{0}{1}{2}{3}{4}{5}{6}{7}"
IL_000b: ldc.i4.8
IL_000c: newarr [System.Runtime]System.Object
IL_0011: dup
IL_0012: ldc.i4.0
IL_0013: ldstr "1"
IL_0018: stelem.ref
IL_0019: dup
IL_001a: ldc.i4.1
IL_001b: ldstr "2"
IL_0020: stelem.ref
IL_0021: dup
IL_0022: ldc.i4.2
IL_0023: ldstr "3"
IL_0028: stelem.ref
IL_0029: dup
IL_002a: ldc.i4.3
IL_002b: ldstr "4"
IL_0030: stelem.ref
IL_0031: dup
IL_0032: ldc.i4.4
IL_0033: ldstr "5"
IL_0038: stelem.ref
IL_0039: dup
IL_003a: ldc.i4.5
IL_003b: ldstr "6"
IL_0040: stelem.ref
IL_0041: dup
IL_0042: ldc.i4.6
IL_0043: ldstr "7"
IL_0048: stelem.ref
IL_0049: dup
IL_004a: ldc.i4.7
IL_004b: ldstr "8"
IL_0050: stelem.ref
IL_0051: call string [System.Runtime]System.String::Format(string,
object[])
IL_0056: pop
IL_0057: ret
} // end of method Program::FormatTest
StringFormat方法虽然是基于StringBuilder，但由于需要遍历字符串来识别占位符，所以比较慢。
3.2Format分次拼接
private static void FormatTest2()
{
string s = string.Empty;
s = string.Format("{0}{1}", s, "1");
s = string.Format("{0}{1}", s, "2");
s = string.Format("{0}{1}", s, "3");
s = string.Format("{0}{1}", s, "4");
s = string.Format("{0}{1}", s, "5");
s = string.Format("{0}{1}", s, "6");
s = string.Format("{0}{1}", s, "7");
s = string.Format("{0}{1}", s, "8");
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void FormatTest2() cil managed
{
// Code size 143 (0x8f)
.maxstack 3
.locals init (string V_0)
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: stloc.0
IL_0006: ldstr "{0}{1}"
IL_000b: ldloc.0
IL_000c: ldstr "1"
IL_0011: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_0016: stloc.0
IL_0017: ldstr "{0}{1}"
IL_001c: ldloc.0
IL_001d: ldstr "2"
IL_0022: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_0027: stloc.0
IL_0028: ldstr "{0}{1}"
IL_002d: ldloc.0
IL_002e: ldstr "3"
IL_0033: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_0038: stloc.0
IL_0039: ldstr "{0}{1}"
IL_003e: ldloc.0
IL_003f: ldstr "4"
IL_0044: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_0049: stloc.0
IL_004a: ldstr "{0}{1}"
IL_004f: ldloc.0
IL_0050: ldstr "5"
IL_0055: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_005a: stloc.0
IL_005b: ldstr "{0}{1}"
IL_0060: ldloc.0
IL_0061: ldstr "6"
IL_0066: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_006b: stloc.0
IL_006c: ldstr "{0}{1}"
IL_0071: ldloc.0
IL_0072: ldstr "7"
IL_0077: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_007c: stloc.0
IL_007d: ldstr "{0}{1}"
IL_0082: ldloc.0
IL_0083: ldstr "8"
IL_0088: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_008d: stloc.0
IL_008e: ret
} // end of method Program::FormatTest2
分次使用Format方法拼接字符串，即分次调用Format方法，多次循环遍历字符串，耗时更长。
4.StringBuilder方法
private static void BuilderTest()
{
StringBuilder sb = new StringBuilder();
sb.Append("1");
sb.Append("2");
sb.Append("3");
sb.Append("4");
sb.Append("5");
sb.Append("6");
sb.Append("7");
sb.Append("8");
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void BuilderTest() cil managed
{
// Code size 101 (0x65)
.maxstack 3
IL_0000: newobj instance void [System.Runtime]System.Text.StringBuilder::.ctor()
IL_0005: dup
IL_0006: ldstr "1"
IL_000b: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0010: pop
IL_0011: dup
IL_0012: ldstr "2"
IL_0017: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_001c: pop
IL_001d: dup
IL_001e: ldstr "3"
IL_0023: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0028: pop
IL_0029: dup
IL_002a: ldstr "4"
IL_002f: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0034: pop
IL_0035: dup
IL_0036: ldstr "5"
IL_003b: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0040: pop
IL_0041: dup
IL_0042: ldstr "6"
IL_0047: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_004c: pop
IL_004d: dup
IL_004e: ldstr "7"
IL_0053: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0058: pop
IL_0059: ldstr "8"
IL_005e: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0063: pop
IL_0064: ret
} // end of method Program::BuilderTest
在短字符串大量拼接的测试中，可以看出一次使用+进行拼接所耗内存最少，所用时间最短。其余方式所耗内存相差不大，但StringBuilder所耗时间明显较短。
由于Format方法内部存在对字符串的遍历，可以推测，随着字符串的长度变长，Format方法所耗时间将会增加。
二、字符串变量拼接（多次循环拼接）
private static void TestPerformanceWithParam<T>(Action<T> action, T t, int times)
{
Stopwatch sw = new Stopwatch();
sw.Start();
for (int i = 0; i < times; i++)
{
action(t);
}
sw.Stop();
Console.WriteLine(action.Method.Name + ", FullTime: " + sw.ElapsedMilliseconds);
}
1.+方法
1.1连续拼接
private static void AddTest(string t)
{
string s = string.Empty;
s = t + t + t + t + t + t + t + t;
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void AddTest(string t) cil managed
{
// Code size 51 (0x33)
.maxstack 8
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: pop
IL_0006: ldc.i4.8
IL_0007: newarr [System.Runtime]System.String
IL_000c: dup
IL_000d: ldc.i4.0
IL_000e: ldarg.0
IL_000f: stelem.ref
IL_0010: dup
IL_0011: ldc.i4.1
IL_0012: ldarg.0
IL_0013: stelem.ref
IL_0014: dup
IL_0015: ldc.i4.2
IL_0016: ldarg.0
IL_0017: stelem.ref
IL_0018: dup
IL_0019: ldc.i4.3
IL_001a: ldarg.0
IL_001b: stelem.ref
IL_001c: dup
IL_001d: ldc.i4.4
IL_001e: ldarg.0
IL_001f: stelem.ref
IL_0020: dup
IL_0021: ldc.i4.5
IL_0022: ldarg.0
IL_0023: stelem.ref
IL_0024: dup
IL_0025: ldc.i4.6
IL_0026: ldarg.0
IL_0027: stelem.ref
IL_0028: dup
IL_0029: ldc.i4.7
IL_002a: ldarg.0
IL_002b: stelem.ref
IL_002c: call string [System.Runtime]System.String::Concat(string[])
IL_0031: pop
IL_0032: ret
} // end of method Program::AddTest
从IL代码可见，在使用+连续拼接字符串变量时，内部调用了String.Concat(string[])方法。
1.2分段拼接
private static void AddWithParamTest2(string t)
{
string s = string.Empty;
s += t;
s += t;
s += t;
s += t;
s += t;
s += t;
s += t;
s += t;
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void AddWithParamTest2(string t) cil managed
{
// Code size 55 (0x37)
.maxstack 8
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: ldarg.0
IL_0006: call string [System.Runtime]System.String::Concat(string,
string)
IL_000b: ldarg.0
IL_000c: call string [System.Runtime]System.String::Concat(string,
string)
IL_0011: ldarg.0
IL_0012: call string [System.Runtime]System.String::Concat(string,
string)
IL_0017: ldarg.0
IL_0018: call string [System.Runtime]System.String::Concat(string,
string)
IL_001d: ldarg.0
IL_001e: call string [System.Runtime]System.String::Concat(string,
string)
IL_0023: ldarg.0
IL_0024: call string [System.Runtime]System.String::Concat(string,
string)
IL_0029: ldarg.0
IL_002a: call string [System.Runtime]System.String::Concat(string,
string)
IL_002f: ldarg.0
IL_0030: call string [System.Runtime]System.String::Concat(string,
string)
IL_0035: pop
IL_0036: ret
} // end of method Program::AddWithParamTest2
2.Concat方法
2.1分次concat
IL代码：
.method private hidebysig static void ConcatTest(string t) cil managed
{
// Code size 55 (0x37)
.maxstack 8
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: ldarg.0
IL_0006: call string [System.Runtime]System.String::Concat(string,
string)
IL_000b: ldarg.0
IL_000c: call string [System.Runtime]System.String::Concat(string,
string)
IL_0011: ldarg.0
IL_0012: call string [System.Runtime]System.String::Concat(string,
string)
IL_0017: ldarg.0
IL_0018: call string [System.Runtime]System.String::Concat(string,
string)
IL_001d: ldarg.0
IL_001e: call string [System.Runtime]System.String::Concat(string,
string)
IL_0023: ldarg.0
IL_0024: call string [System.Runtime]System.String::Concat(string,
string)
IL_0029: ldarg.0
IL_002a: call string [System.Runtime]System.String::Concat(string,
string)
IL_002f: ldarg.0
IL_0030: call string [System.Runtime]System.String::Concat(string,
string)
IL_0035: pop
IL_0036: ret
} // end of method Program::ConcatTest
从IL代码来看，同使用+分段拼接相似。
2.2一次拼接
IL代码：
.method private hidebysig static void ConcatTest2(string t) cil managed
{
// Code size 56 (0x38)
.maxstack 4
.locals init (string V_0)
IL_0000: ldsfld string [System.Runtime]System.String::Empty
IL_0005: stloc.0
IL_0006: ldc.i4.s 9
IL_0008: newarr [System.Runtime]System.String
IL_000d: dup
IL_000e: ldc.i4.0
IL_000f: ldloc.0
IL_0010: stelem.ref
IL_0011: dup
IL_0012: ldc.i4.1
IL_0013: ldarg.0
IL_0014: stelem.ref
IL_0015: dup
IL_0016: ldc.i4.2
IL_0017: ldarg.0
IL_0018: stelem.ref
IL_0019: dup
IL_001a: ldc.i4.3
IL_001b: ldarg.0
IL_001c: stelem.ref
IL_001d: dup
IL_001e: ldc.i4.4
IL_001f: ldarg.0
IL_0020: stelem.ref
IL_0021: dup
IL_0022: ldc.i4.5
IL_0023: ldarg.0
IL_0024: stelem.ref
IL_0025: dup
IL_0026: ldc.i4.6
IL_0027: ldarg.0
IL_0028: stelem.ref
IL_0029: dup
IL_002a: ldc.i4.7
IL_002b: ldarg.0
IL_002c: stelem.ref
IL_002d: dup
IL_002e: ldc.i4.8
IL_002f: ldarg.0
IL_0030: stelem.ref
IL_0031: call string [System.Runtime]System.String::Concat(string[])
IL_0036: stloc.0
IL_0037: ret
} // end of method Program::ConcatTest2
从IL代码可以看出，同使用+一次拼接相似。
3.Format
private static void FormatTest(string t)
{
string s = string.Format("{0}{1}{2}{3}{4}{5}{6}{7}", t, t, t, t, t, t, t, t);
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void FormatTest(string t) cil managed
{
// Code size 50 (0x32)
.maxstack 8
IL_0000: ldstr "{0}{1}{2}{3}{4}{5}{6}{7}"
IL_0005: ldc.i4.8
IL_0006: newarr [System.Runtime]System.Object
IL_000b: dup
IL_000c: ldc.i4.0
IL_000d: ldarg.0
IL_000e: stelem.ref
IL_000f: dup
IL_0010: ldc.i4.1
IL_0011: ldarg.0
IL_0012: stelem.ref
IL_0013: dup
IL_0014: ldc.i4.2
IL_0015: ldarg.0
IL_0016: stelem.ref
IL_0017: dup
IL_0018: ldc.i4.3
IL_0019: ldarg.0
IL_001a: stelem.ref
IL_001b: dup
IL_001c: ldc.i4.4
IL_001d: ldarg.0
IL_001e: stelem.ref
IL_001f: dup
IL_0020: ldc.i4.5
IL_0021: ldarg.0
IL_0022: stelem.ref
IL_0023: dup
IL_0024: ldc.i4.6
IL_0025: ldarg.0
IL_0026: stelem.ref
IL_0027: dup
IL_0028: ldc.i4.7
IL_0029: ldarg.0
IL_002a: stelem.ref
IL_002b: call string [System.Runtime]System.String::Format(string,
object[])
IL_0030: pop
IL_0031: ret
} // end of method Program::FormatTest
时间的损耗主要来自于String.Format方法。
4.StringBuilder方法
private static void BuilderTest(string t)
{
StringBuilder sb = new StringBuilder();
sb.Append(t);
sb.Append(t);
sb.Append(t);
sb.Append(t);
sb.Append(t);
sb.Append(t);
sb.Append(t);
sb.Append(t);
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void BuilderTest(string t) cil managed
{
// Code size 69 (0x45)
.maxstack 3
IL_0000: newobj instance void [System.Runtime]System.Text.StringBuilder::.ctor()
IL_0005: dup
IL_0006: ldarg.0
IL_0007: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_000c: pop
IL_000d: dup
IL_000e: ldarg.0
IL_000f: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0014: pop
IL_0015: dup
IL_0016: ldarg.0
IL_0017: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_001c: pop
IL_001d: dup
IL_001e: ldarg.0
IL_001f: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0024: pop
IL_0025: dup
IL_0026: ldarg.0
IL_0027: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_002c: pop
IL_002d: dup
IL_002e: ldarg.0
IL_002f: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0034: pop
IL_0035: dup
IL_0036: ldarg.0
IL_0037: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_003c: pop
IL_003d: ldarg.0
IL_003e: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_0043: pop
IL_0044: ret
} // end of method Program::BuilderTest
在短字符串（上面所用字符串为“short”）大量循环拼接（上述结果为每个方法循环执行一千万次）时，四种方法的差距并不明显。
当字符串变长后，可见运行结果差距拉大：
此时StringBuilder仍没有明显的优势。
三、字符串变量拼接（循环拼接至一个字符串）
1.+方法
private static void TestAddVeryLong(string s, int times)
{
Stopwatch sw = new Stopwatch();
sw.Start();
string str = string.Empty;
for(int i = 0; i < times; i++)
{
str += s;
}
sw.Stop();
Console.WriteLine("add very long: " + sw.ElapsedMilliseconds);
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void TestAddVeryLong(string s,
int32 times) cil managed
{
// Code size 71 (0x47)
.maxstack 2
.locals init (class [System.Runtime.Extensions]System.Diagnostics.Stopwatch V_0,
string V_1,
int32 V_2)
IL_0000: newobj instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::.ctor()
IL_0005: stloc.0
IL_0006: ldloc.0
IL_0007: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Start()
IL_000c: ldsfld string [System.Runtime]System.String::Empty
IL_0011: stloc.1
IL_0012: ldc.i4.0
IL_0013: stloc.2
IL_0014: br.s IL_0022
IL_0016: ldloc.1
IL_0017: ldarg.0
IL_0018: call string [System.Runtime]System.String::Concat(string,
string)
IL_001d: stloc.1
IL_001e: ldloc.2
IL_001f: ldc.i4.1
IL_0020: add
IL_0021: stloc.2
IL_0022: ldloc.2
IL_0023: ldarg.1
IL_0024: blt.s IL_0016
IL_0026: ldloc.0
IL_0027: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Stop()
IL_002c: ldstr "add very long: "
IL_0031: ldloc.0
IL_0032: callvirt instance int64 [System.Runtime.Extensions]System.Diagnostics.Stopwatch::get_ElapsedMilliseconds()
IL_0037: box [System.Runtime]System.Int64
IL_003c: call string [System.Runtime]System.String::Concat(object,
object)
IL_0041: call void [System.Console]System.Console::WriteLine(string)
IL_0046: ret
} // end of method Program::TestAddVeryLong
2.Concat方法
private static void TestConcatVeryLong(string s, int times)
{
Stopwatch sw = new Stopwatch();
sw.Start();
string str = string.Empty;
for (int i = 0; i < times; i++)
{
str = string.Concat(str, s);
}
sw.Stop();
Console.WriteLine("concat very long: " + sw.ElapsedMilliseconds);
}
IL代码：
.method private hidebysig static void TestConcatVeryLong(string s,
int32 times) cil managed
{
// Code size 71 (0x47)
.maxstack 2
.locals init (class [System.Runtime.Extensions]System.Diagnostics.Stopwatch V_0,
string V_1,
int32 V_2)
IL_0000: newobj instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::.ctor()
IL_0005: stloc.0
IL_0006: ldloc.0
IL_0007: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Start()
IL_000c: ldsfld string [System.Runtime]System.String::Empty
IL_0011: stloc.1
IL_0012: ldc.i4.0
IL_0013: stloc.2
IL_0014: br.s IL_0022
IL_0016: ldloc.1
IL_0017: ldarg.0
IL_0018: call string [System.Runtime]System.String::Concat(string,
string)
IL_001d: stloc.1
IL_001e: ldloc.2
IL_001f: ldc.i4.1
IL_0020: add
IL_0021: stloc.2
IL_0022: ldloc.2
IL_0023: ldarg.1
IL_0024: blt.s IL_0016
IL_0026: ldloc.0
IL_0027: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Stop()
IL_002c: ldstr "concat very long: "
IL_0031: ldloc.0
IL_0032: callvirt instance int64 [System.Runtime.Extensions]System.Diagnostics.Stopwatch::get_ElapsedMilliseconds()
IL_0037: box [System.Runtime]System.Int64
IL_003c: call string [System.Runtime]System.String::Concat(object,
object)
IL_0041: call void [System.Console]System.Console::WriteLine(string)
IL_0046: ret
} // end of method Program::TestConcatVeryLong
由IL代码可见，和使用+性能相似。
3.Format方法
private static void TestFormatVeryLong(string s, int times)
{
Stopwatch sw = new Stopwatch();
sw.Start();
string str = string.Empty;
for (int i = 0; i < times; i++)
{
str = string.Format("{0}{1}", str, s);
}
sw.Stop();
Console.WriteLine("format very long: " + sw.ElapsedMilliseconds);
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void TestFormatVeryLong(string s,
int32 times) cil managed
{
// Code size 76 (0x4c)
.maxstack 3
.locals init (class [System.Runtime.Extensions]System.Diagnostics.Stopwatch V_0,
string V_1,
int32 V_2)
IL_0000: newobj instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::.ctor()
IL_0005: stloc.0
IL_0006: ldloc.0
IL_0007: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Start()
IL_000c: ldsfld string [System.Runtime]System.String::Empty
IL_0011: stloc.1
IL_0012: ldc.i4.0
IL_0013: stloc.2
IL_0014: br.s IL_0027
IL_0016: ldstr "{0}{1}"
IL_001b: ldloc.1
IL_001c: ldarg.0
IL_001d: call string [System.Runtime]System.String::Format(string,
object,
object)
IL_0022: stloc.1
IL_0023: ldloc.2
IL_0024: ldc.i4.1
IL_0025: add
IL_0026: stloc.2
IL_0027: ldloc.2
IL_0028: ldarg.1
IL_0029: blt.s IL_0016
IL_002b: ldloc.0
IL_002c: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Stop()
IL_0031: ldstr "format very long: "
IL_0036: ldloc.0
IL_0037: callvirt instance int64 [System.Runtime.Extensions]System.Diagnostics.Stopwatch::get_ElapsedMilliseconds()
IL_003c: box [System.Runtime]System.Int64
IL_0041: call string [System.Runtime]System.String::Concat(object,
object)
IL_0046: call void [System.Console]System.Console::WriteLine(string)
IL_004b: ret
} // end of method Program::TestFormatVeryLong
4.StringBuilder方法
private static void TestBuilderVeryLong(string s, int times)
{
Stopwatch sw = new Stopwatch();
sw.Start();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < times; i++)
{
sb.Append(s);
}
sw.Stop();
Console.WriteLine("builder very long: " + sw.ElapsedMilliseconds);
}
运行时间：
内存情况：
IL代码：
.method private hidebysig static void TestBuilderVeryLong(string s,
int32 times) cil managed
{
// Code size 71 (0x47)
.maxstack 2
.locals init (class [System.Runtime.Extensions]System.Diagnostics.Stopwatch V_0,
class [System.Runtime]System.Text.StringBuilder V_1,
int32 V_2)
IL_0000: newobj instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::.ctor()
IL_0005: stloc.0
IL_0006: ldloc.0
IL_0007: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Start()
IL_000c: newobj instance void [System.Runtime]System.Text.StringBuilder::.ctor()
IL_0011: stloc.1
IL_0012: ldc.i4.0
IL_0013: stloc.2
IL_0014: br.s IL_0022
IL_0016: ldloc.1
IL_0017: ldarg.0
IL_0018: callvirt instance class [System.Runtime]System.Text.StringBuilder [System.Runtime]System.Text.StringBuilder::Append(string)
IL_001d: pop
IL_001e: ldloc.2
IL_001f: ldc.i4.1
IL_0020: add
IL_0021: stloc.2
IL_0022: ldloc.2
IL_0023: ldarg.1
IL_0024: blt.s IL_0016
IL_0026: ldloc.0
IL_0027: callvirt instance void [System.Runtime.Extensions]System.Diagnostics.Stopwatch::Stop()
IL_002c: ldstr "builder very long: "
IL_0031: ldloc.0
IL_0032: callvirt instance int64 [System.Runtime.Extensions]System.Diagnostics.Stopwatch::get_ElapsedMilliseconds()
IL_0037: box [System.Runtime]System.Int64
IL_003c: call string [System.Runtime]System.String::Concat(object,
object)
IL_0041: call void [System.Console]System.Console::WriteLine(string)
IL_0046: ret
} // end of method Program::TestBuilderVeryLong
这个差距在拼接字符串更多的时候会更加明显。
拼接一千万次时，+方法运行一个多小时仍无法得出结果：
而StringBuilder只需要102ms。
+方法的问题在于由于string的特殊性，每次操作都将新开辟内存空间，随着字符串长度的增加、操作次数的增加等，+方法所耗费的内存会越来越大。
而StringBuilder则可以在原有的内存空间中进行修改和扩张，在进行频繁、长串的操作时极大地提高了效率。
显然，如果是不频繁、短字符串的拼接，使用哪种方式拼接字符串没有明显的性能差别（Format可能稍差一些），但如果是频繁的长串操作，StringBuilder具有绝对的优势。
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