C#通過不安全程式碼看記憶體載入
阿新 • • 發佈：2022-12-09
（注：本篇用點長，有點繞，耐心瀏覽）
C#中型別分為值型別和引用型別，值型別儲存在堆疊中，是棧結構，先進後出，引用型別儲存在託管堆中。接下來用不安全程式碼的地址，來看一下值型別和引用型別的儲存。
專案檔案
C#中使用不安全程式碼需要在專案檔案中新增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型別的變數，然後檢視它的記憶體地址，然後進行呼叫一個方法進行相加運算，然後分別在方法內輸出變數和結查記憶體地址，最後返回主方法後變數的記憶體地址。
值型別：
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的所在記憶體地址大於v2，最後運算完的v3是最小的，我們可以想象，v1放在棧的最後面，地址最大，然後放v2，最後放v3。回收時的順序是反回來的。那麼Add方法裡，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，最後是v3進棧，不過TestDouble裡的每個變數都相差8，但方法裡的就不是了，這是因為方法引數，返回值等資訊，還要佔一些記憶體空間。還有TestDouble的v3為什麼能和v2相差8？不是有Add方法嗎？原因是Add呼叫完後都出棧了，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物件地址= " + (long)&v1);
var v2 = new TestStruct();
Console.WriteLine("TestStruct原v2物件地址= " + (long)&v2);
Console.WriteLine("TestStruct v2-v1 " + ((long)&v2 - (long)&v1));
var v3 = Add(v1, v2);
Console.WriteLine("TestStruct原v3物件地址= " + (long)&v3);
Console.WriteLine("TestStruct v3-v2 " + ((long)&v3 - (long)&v2));
}
static TestStruct Add(TestStruct v1, TestStruct v2)
{
Console.WriteLine("Add TestStruct v1物件地址= " + (long)&v1);
Console.WriteLine("Add TestStruct v2物件地址= " + (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物件地址" + (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。
引用型別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字串地址= " + (long)p);
}
fixed (char* p = v2)
{
ad2 = (long)p;
Console.WriteLine("TestString v2字串地址= " + (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字串地址= " + (long)p);
}
fixed (char* p = v2)
{
ad2 = (long)p;
Console.WriteLine("Add中v2字串地址= " + (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物件地址= " + (long)h1.AddrOfPinnedObject());
var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
Console.WriteLine("TestString2 v2物件地址= " + (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物件地址= " + (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物件地址= " + (long)h1.AddrOfPinnedObject());
var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
Console.WriteLine("Add2中的v2物件地址= " + (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物件地址= " + (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;
}
字串是引用型別，v1比v2記憶體地址小，進入Add後，v1和v2與傳入的地址相同，因為是引用型別，Add方法裡的v3接著往大走，並且與返回的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，因為字串有留用性，所以兩個方法的v1和v2是一樣的；但兩種方式呼叫了Add後，在Add裡的v3都是aaaabbbb，都是拼接，但拼出來的字串的地址不相同，所以這塊沒有留用。
自定class型別
class TestClass
{
public int i = 100;
}
static void TestTestClass()
{
var v1 = new TestClass();
var h1 = GCHandle.Alloc(v1, GCHandleType.Pinned);
Console.WriteLine("TestTestClass v1物件地址= " + (long)h1.AddrOfPinnedObject());
var v2 = new TestClass();
var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
Console.WriteLine("TestTestClass v2物件地址= " + (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物件地址= " + (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物件地址= " + (long)h1.AddrOfPinnedObject());
var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
Console.WriteLine("Add中的v2物件地址= " + (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物件地址= " + (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，並且地址都是在增加。
當然引用型別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，不過程式碼量少的情況也不一定能觸發回收。
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