一 编译预处理

1 标识符声明

① #define定义一个标识符；
② #undef 取消定 一个标识符；

2 条件处理

#if #elif #else #endif

3 信息报告

#error和#warning

4 行号标记

#line 行号“文件名”

二 unsafe及指针

1 unsafe

用于修饰类、方法等

2 fixed及指针

fixed(类型*指针名=表达式)语句；

3 sizeof运算符

sizeof(简单或结构类型名)

4 stackalloc

在栈上分配的内存，而不是在堆上，因此不会担心内存被垃圾回收器自动回收；

5 指针示例

class FileStream:Stream
{int handle;[dllimport("kernel32",SetLastError=true)]static extern unsafe bool ReadFile(int hFile,void*lpBuffer,int nBytesToRead,int* nBytesRead,Overlapped*lpOverlapped);public unsafe int Read(byte[] buffer,int index,int count){int n=0;fixed(byte*p=buffer){ReadFile(handle,p+index,count,&n,null);}return n;}
}

指针

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace 指针
{class Test{static unsafe void Copy(byte[] src, byte[] dst, int count){int srcLen = src.Length;int desLen = dst.Length;if(srcLenthrow new ArgumentException();}fixed(byte* pSrc=src,pDst=dst){byte* ps = pSrc;byte* pd = pDst;for(int n=0;n*pd++ = *ps++;}}}static void Main(){byte[] a = new byte[100];byte[] b= new byte[100];for (int i = 0; i < 100; ++i)a[i] = (byte)i;Copy(a, b, 100);Console.WriteLine("The first 10 elements are:");for (int i = 0; i < 10; ++i)Console.Write(b[i] + "{0}", i < 9 ? " " : " ");Console.WriteLine("\n");Console.ReadKey();}}
}

stackalloc分配内存空间

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace 分配内存空间
{class Test{unsafe static string IntToString(int value){char* buffer = stackalloc char[16];char* p = buffer + 16;int n = value >= 0 ? value : -value;do{*--p = (char)(n % 10 + '0');n /= 10;} while (n != 0);if (value < 0) *--p = '-';return new string(p, 0, (int)(buffer + 16 - p));}static void Main(){Console.WriteLine(IntToString(12345));Console.WriteLine(IntToString(-999));Console.ReadKey();}}
}