主题：【文摘】C/C++圣战！ -- aircobra

While practically every pointer type construct in C or C++ has a reference type counterpart in C#, nonetheless, there are situations where access to pointer types becomes a necessity. For example, interfacing with the underlying operating system, accessing a memory-mapped device, or implementing a time-critical algorithm may not be possible or practical without access to pointers. To address this need, C# provides the ability to write unsafe code.

In unsafe code it is possible to declare and operate on pointers, to perform conversions between pointers and integral types, to take the address of variables, and so forth. In a sense, writing unsafe code is much like writing C code within a C# program.

Unsafe code is in fact a "safe" feature from the perspective of both developers and users. Unsafe code must be clearly marked with the modifier unsafe, so developers can't possibly use unsafe features accidentally, and the execution engine works to ensure that unsafe code cannot be executed in an untrusted environment.

顺便看一个小例子

using System;

class Test

{

static int value = 20;

unsafe static void F(out int* pi1, ref int* pi2) {

int i = 10;

pi1 = &i;

fixed (int* pj = &value) {

// ...

pi2 = pj;

}

}

static void Main() {

int i = 10;

unsafe {

int* px1;

int* px2 = &i;

F(out px1, ref px2);

Console.WriteLine("*px1 = {0}, *px2 = {1}",

*px1, *px2); // undefined behavior

}

}

}