（注：本篇用點長，有點繞，耐心瀏覽）

C#中類型分為值類型和引用類型，值類型存儲在堆棧中，是棧結構，先進后出，引用類型存儲在托管堆中。接下來用不安全代碼的地址，來看一下值類型和引用類型的存儲。

項目文件

C#中使用不安全代碼需要在項目文件中添加AllowUnsafeBlocks配置。

<Project?Sdk="Microsoft.NET.Sdk"><PropertyGroup><OutputType>Exe</OutputType><TargetFramework>net7.0</TargetFramework><ImplicitUsings>enable</ImplicitUsings><Nullable>enable</Nullable><AllowUnsafeBlocks>true</AllowUnsafeBlocks></PropertyGroup>
</Project>

所有的測試案例都是定義兩個特定類型的變量，然后查看它的內存地址，然后進行調用一個方法進行相加運算，然后分別在方法內輸出變量和結查內存地址，最后返回主方法后變量的內存地址。

值類型：

static void TestDouble()
{var v1 = 1.00001d;var v2 = 2.00002d;Console.WriteLine("TestDouble v1 " + (long)&v1);Console.WriteLine("TestDouble v2 " + (long)&v2);Console.WriteLine("TestDouble v2-v1 " + ((long)&v2 - (long)&v1));var v3 = Add(v1, v2);Console.WriteLine("TestDouble v3 " + (long)&v3);Console.WriteLine("TestDouble v3-v2 " + ((long)&v3 - (long)&v2));Console.WriteLine("TestDouble v3-v1 " + ((long)&v3 - (long)&v1));
}static double Add(double v1, double v2)
{Console.WriteLine("Add v1 " + (long)&v1);Console.WriteLine("Add v2 " + (long)&v2);Console.WriteLine("Add v2-v1 " + ((long)&v2 - (long)&v1));var v3 = v1 + v2;Console.WriteLine("Add v3 " + (long)&v3);Console.WriteLine("Add v3-v2 " + ((long)&v3 - (long)&v2));Console.WriteLine("Add v3-v1 " + ((long)&v3 - (long)&v1));return v3;
}

v1的所在內存地址大于v2，最后運算完的v3是最小的，我們可以想象，v1放在棧的最后面，地址最大，然后放v2，最后放v3。回收時的順序是反回來的。那么Add方法里，v2地址最大，但比TestDouble都要小，說明進棧要晚一些，接下來是v1進棧，最后是v3進棧，不過TestDouble里的每個變量都相差8，但方法里的就不是了，這是因為方法參數，返回值等信息，還要占一些內存空間。還有TestDouble的v3為什么能和v2相差8？不是有Add方法嗎？原因是Add調用完后都出棧了，所以TestDouble的v3和v2是相鄰的。

自定義結構體：

struct TestStruct
{public TestStruct(){i = 100;}public long i;
}
static void TestTestStruct()
{var v1 = new TestStruct();Console.WriteLine("TestStruct原v1對象地址= " + (long)&v1);var v2 = new TestStruct();Console.WriteLine("TestStruct原v2對象地址= " + (long)&v2);Console.WriteLine("TestStruct v2-v1 " + ((long)&v2 - (long)&v1));var?v3?=?Add(v1,?v2);Console.WriteLine("TestStruct原v3對象地址= " + (long)&v3);Console.WriteLine("TestStruct v3-v2 " + ((long)&v3 - (long)&v2));
}
static TestStruct Add(TestStruct v1, TestStruct v2)
{Console.WriteLine("Add TestStruct v1對象地址= " + (long)&v1);Console.WriteLine("Add TestStruct v2對象地址= " + (long)&v2);Console.WriteLine("Add TestStruct  v2-v1 " + ((long)&v2 - (long)&v1));var v3 = new TestStruct();v3.i = v1.i + v2.i;Console.WriteLine("Add TestStruct v3對象地址" + (long)&v3);Console.WriteLine("Add TestStruct  v3-v2 " + ((long)&v3 - (long)&v2));return v3;
}

自定義struct與double類似，本質上double也是用struct定義的。

引用類型string

static void TestString()
{long ad1, ad2, ad3;var v1 = "aaaa";var v2 = "bbbb";fixed (char* p = v1){ad1 = (long)p;Console.WriteLine("TestString v1字符串地址= " + (long)p);}fixed (char* p = v2){ad2 = (long)p;Console.WriteLine("TestString v2字符串地址= " + (long)p);}Console.WriteLine("TestString v2-v1 " + (ad2 - ad1));var v3 = Add(v1, v2);fixed (char* p = v3){ad3 = (long)p;Console.WriteLine("TestString v3字符串地址= " + (long)p);}Console.WriteLine("TestString v3-v2 " + (ad3 - ad2));
}static string Add(string v1, string v2)
{long ad1, ad2, ad3;fixed (char* p = v1){ad1 = (long)p;Console.WriteLine("Add中v1字符串地址= " + (long)p);}fixed (char* p = v2){ad2 = (long)p;Console.WriteLine("Add中v2字符串地址= " + (long)p);}Console.WriteLine("Add中 v2-v1 " + (ad2 - ad1));var v3 = v1 + v2;fixed (char* p = v3){ad3 = (long)p;Console.WriteLine("Add中v3字符串地址= " + (long)p);}Console.WriteLine("Add中 v3-v2 " + (ad3 - ad2));Console.WriteLine("Add中 v3-v1 " + (ad3 - ad1));return v3;
}
static void TestString2()
{var v1 = "aaaa";var v2 = "bbbb";var h1 = GCHandle.Alloc(v1, GCHandleType.Pinned);Console.WriteLine("TestString2 v1對象地址= " + (long)h1.AddrOfPinnedObject());var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);Console.WriteLine("TestString2 v2對象地址= " + (long)h2.AddrOfPinnedObject());Console.WriteLine("TestString2 v2-v1 " + ((long)h2.AddrOfPinnedObject() - (long)h1.AddrOfPinnedObject()));var v3 = Add2(v1, v2);var h3 = GCHandle.Alloc(v3, GCHandleType.Pinned);Console.WriteLine("TestString2 v3對象地址= " + (long)h3.AddrOfPinnedObject());Console.WriteLine("TestString2 v3-v2 " + ((long)h3.AddrOfPinnedObject() - (long)h2.AddrOfPinnedObject()));
}
static string Add2(string v1, string v2)
{var h1 = GCHandle.Alloc(v1, GCHandleType.Pinned);Console.WriteLine("Add2中的v1對象地址= " + (long)h1.AddrOfPinnedObject());var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);Console.WriteLine("Add2中的v2對象地址= " + (long)h2.AddrOfPinnedObject());Console.WriteLine("Add2 v2-v1 " + ((long)h2.AddrOfPinnedObject() - (long)h1.AddrOfPinnedObject()));var v3 = v1 + v2;var h3 = GCHandle.Alloc(v3, GCHandleType.Pinned);Console.WriteLine("Add2中的v3對象地址= " + (long)h3.AddrOfPinnedObject());Console.WriteLine("Add2 v3-v2 " + ((long)h3.AddrOfPinnedObject() - (long)h2.AddrOfPinnedObject()));Console.WriteLine("Add2 v3-v1 " + ((long)h3.AddrOfPinnedObject() - (long)h1.AddrOfPinnedObject()));return v3;
}

字符串是引用類型，v1比v2內存地址小，進入Add后，v1和v2與傳入的地址相同，因為是引用類型，Add方法里的v3接著往大走，并且與返回的v3是一個地址，這些沒有問題。

string用了兩種方法，發現兩個方式v1都是aaaa,v2都是bbbb，因為字符串有留用性，所以兩個方法的v1和v2是一樣的；但兩種方式調用了Add后，在Add里的v3都是aaaabbbb，都是拼接，但拼出來的字符串的地址不相同，所以這塊沒有留用。

自定class類型

class?TestClass
{public int i = 100;
}
static void TestTestClass()
{var v1 = new TestClass();var h1 = GCHandle.Alloc(v1, GCHandleType.Pinned);Console.WriteLine("TestTestClass v1對象地址= " + (long)h1.AddrOfPinnedObject());var v2 = new TestClass();var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);Console.WriteLine("TestTestClass v2對象地址= " + (long)h2.AddrOfPinnedObject());Console.WriteLine("TestTestClass?v2-v1?"?+?((long)h2.AddrOfPinnedObject()?-?(long)h1.AddrOfPinnedObject()));var?v3?=?Add(v1,?v2);var h3 = GCHandle.Alloc(v3, GCHandleType.Pinned);Console.WriteLine("TestTestClass 3對象地址= " + (long)h3.AddrOfPinnedObject());Console.WriteLine("TestTestClass?v3-v2?"?+?((long)h3.AddrOfPinnedObject()?-?(long)h2.AddrOfPinnedObject()));
}
static TestClass Add(TestClass v1, TestClass v2)
{var h1 = GCHandle.Alloc(v1, GCHandleType.Pinned);Console.WriteLine("Add中的v1對象地址= " + (long)h1.AddrOfPinnedObject());var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);Console.WriteLine("Add中的v2對象地址= " + (long)h2.AddrOfPinnedObject());Console.WriteLine("Add中?v2-v1?"?+?((long)h2.AddrOfPinnedObject()?-?(long)h1.AddrOfPinnedObject()));var?v3?=?new?TestClass();v3.i = v1.i + v2.i;var h3 = GCHandle.Alloc(v3, GCHandleType.Pinned);Console.WriteLine("Add中的v3對象地址= " + (long)h3.AddrOfPinnedObject());Console.WriteLine("Add中 v3-v2 " + ((long)h3.AddrOfPinnedObject() - (long)h2.AddrOfPinnedObject()));Console.WriteLine("Add中 v3-v1 " + ((long)h3.AddrOfPinnedObject() - (long)h1.AddrOfPinnedObject()));return v3;
}

自定義class，每次都是新地址，沒有留用性，并且地址都是在增加。

當然引用類型的地址不是一成不變的，因為有垃圾回放，重新整理的過程，本例用用Pinned的方式固定，不過代碼量少的情況也不一定能觸發回收。