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C#通過(guò)不安全代碼看內(nèi)存加載的示例詳解_C#教程

作者：桂素偉 ? 更新時(shí)間： 2022-09-14 編程語(yǔ)言

C#中類(lèi)型分為值類(lèi)型和引用類(lèi)型，值類(lèi)型存儲(chǔ)在堆棧中，是棧結(jié)構(gòu)，先進(jìn)后出，引用類(lèi)型存儲(chǔ)在托管堆中。接下來(lái)用不安全代碼的地址，來(lái)看一下值類(lèi)型和引用類(lèi)型的存儲(chǔ)。

項(xiàng)目文件

C#中使用不安全代碼需要在項(xiàng)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(cè)試案例都是定義兩個(gè)特定類(lèi)型的變量，然后查看它的內(nèi)存地址，然后進(jìn)行調(diào)用一個(gè)方法進(jìn)行相加運(yùn)算，然后分別在方法內(nèi)輸出變量和結(jié)查內(nèi)存地址，最后返回主方法后變量的內(nèi)存地址。

值類(lèi)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(nèi)存地址大于v2，最后運(yùn)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(shí)的順序是反回來(lái)的。那么Add方法里，v2地址最大，但比TestDouble都要小，說(shuō)明進(jìn)棧要晚一些，接下來(lái)是v1進(jìn)棧，最后是v3進(jìn)棧，不過(guò)TestDouble里的每個(gè)變量都相差8，但方法里的就不是了，這是因?yàn)榉椒▍?shù)，返回值等信息，還要占一些內(nèi)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(diào)用完后都出棧了，所以TestDouble的v3和v2是相鄰的。

自定義結(jié)構(gòu)體

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

自定義struct與double類(lèi)似，本質(zhì)上double也是用struct定義的。

引用類(lèi)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(duì)象地址= " + (long)h1.AddrOfPinnedObject());
    var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
    Console.WriteLine("TestString2 v2對(duì)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(duì)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(duì)象地址= " + (long)h1.AddrOfPinnedObject());
    var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
    Console.WriteLine("Add2中的v2對(duì)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(duì)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(lèi)型，v1比v2內(nèi)存地址小，進(jìn)入Add后，v1和v2與傳入的地址相同，因?yàn)槭且妙?lèi)型，Add方法里的v3接著往大走，并且與返回的v3是一個(gè)地址，這些沒(méi)有問(wèn)題。

string用了兩種方法，發(fā)現(xiàn)兩個(gè)方式v1都是aaaa,v2都是bbbb，因?yàn)樽址辛粲眯?，所以?xún)蓚€(gè)方法的v1和v2是一樣的；但兩種方式調(diào)用了Add后，在Add里的v3都是aaaabbbb，都是拼接，但拼出來(lái)的字符串的地址不相同，所以這塊沒(méi)有留用。

自定class類(lèi)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(duì)象地址= " + (long)h1.AddrOfPinnedObject());
    var v2 = new TestClass();
    var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
    Console.WriteLine("TestTestClass v2對(duì)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(duì)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(duì)象地址= " + (long)h1.AddrOfPinnedObject());
    var h2 = GCHandle.Alloc(v2, GCHandleType.Pinned);
    Console.WriteLine("Add中的v2對(duì)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(duì)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(méi)有留用性，并且地址都是在增加。

當(dāng)然引用類(lèi)型的地址不是一成不變的，因?yàn)橛欣胤牛匦抡淼倪^(guò)程，本例用用Pinned的方式固定，不過(guò)代碼量少的情況也不一定能觸發(fā)回收。

原文鏈接：https://mp.weixin.qq.com/s/TmiJUXbVBxC-ZNlpAI5xwQ

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