C#fixed关键字 - 爱码网

固定大小缓冲区。

C# 编译器只允许在 fixed 语句中分配指向托管变量的指针。

unsafe static void TestMethod() 
{ 
 
    // Assume that the following class exists. 
    //class Point  
    //{  
    //    public int x; 
    //    public int y;  
    //} 
 
    // Variable pt is a managed variable, subject to garbage collection. 
    Point pt = new Point(); 
 
    // Using fixed allows the address of pt members to be taken, 
    // and "pins" pt so that it is not relocated. 
 
    fixed (int* p = &pt.x) 
    { 
        *p = 1; 
    }         
 
}

固定大小的缓冲区（C# 编程指南）。

只要指针的类型相同，就可以初始化多个指针。

fixed (byte* ps = srcarray, pd = dstarray) {...}

要初始化不同类型的指针，只需嵌套 fixed 语句，如下面的示例所示。

// Do something with p1 and p2. 
    } 
}

因此，不要指向 fixed 语句之外的那些变量。

static unsafe void Test2() 
{ 
    Point point = new Point(); 
    double[] arr = { 0, 1.5, 2.3, 3.4, 4.0, 5.9 }; 
    string str = "Hello World"; 
 
    // The following two assignments are equivalent. Each assigns the address 
    // of the first element in array arr to pointer p. 
 
    // You can initialize a pointer by using an array. 
    fixed (double* p = arr) { /*...*/ } 
 
    // You can initialize a pointer by using the address of a variable.  
    fixed (double* p = &arr[0]) { /*...*/ } 
 
    // The following assignment initializes p by using a string. 
    fixed (char* p = str) { /*...*/ } 
 
    // The following assignment is not valid, because str[0] is a char,  
    // which is a value, not a variable. 
    //fixed (char* p = &str[0]) { /*...*/ }  
 
 
    // You can initialize a pointer by using the address of a variable, such 
    // as point.x or arr[5]. 
    fixed (int* p1 = &point.x) 
    { 
        fixed (double* p2 = &arr[5]) 
        { 
            // Do something with p1 and p2. 
        } 
    } 
}

注意
无法修改在 fixed 语句中初始化的指针。

stackalloc。

class Point 
{  
    public int x, y;  
}

class FixedTest2  
{ 
    // Unsafe method: takes a pointer to an int. 
    unsafe static void SquarePtrParam (int* p)  
    { 
        *p *= *p; 
    } 
 
    unsafe static void Main()  
    { 
        Point pt = new Point(); 
        pt.x = 5; 
        pt.y = 6; 
        // Pin pt in place: 
        fixed (int* p = &pt.x)  
        { 
            SquarePtrParam (p); 
        } 
        // pt now unpinned. 
        Console.WriteLine ("{0} {1}", pt.x, pt.y); 
    } 
} 
/* 
Output: 
25 6 
 */