fixed 语句设置指向托管变量的指针并在 statement 执行期间“钉住”该变量。如果没有 fixed 语句,则指向可移动托管变量的指针的作用很小,因为垃圾回收可能不可预知地重定位变量。C# 编译器只允许在 fixed 语句中分配指向托管变量的指针。// statements_fixed.cs // compile with: /unsafe using System;class Point { public int x, y; }class FixedTest { // 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:// assume class Point { public int x, y; } // 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 it isn't relocated. fixed (int* p = &pt.x) { SquarePtrParam (p); } // pt now unpinned //执行完语句中的代码后,任何固定变量都被解除固定并受垃圾回收的制约。因此,不要指向 fixed 语句之外的那些变量。 Console.WriteLine ("{0} {1}", pt.x, pt.y); } } 你最好再看下 固定变量和可移动变量
unsafe static void voidPoint(void* pTwinCatInputs)
{
void** ppInputBlock = &pTwinCatInputs;
}
// compile with: /unsafe
using System;class Point
{
public int x, y;
}class FixedTest
{
// 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:// assume class Point { public int x, y; }
// 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 it isn't relocated. fixed (int* p = &pt.x)
{
SquarePtrParam (p);
}
// pt now unpinned
//执行完语句中的代码后,任何固定变量都被解除固定并受垃圾回收的制约。因此,不要指向 fixed 语句之外的那些变量。
Console.WriteLine ("{0} {1}", pt.x, pt.y);
}
}
你最好再看下
固定变量和可移动变量