如何分配的byte []在C＃中的指针 [英] How to assign byte[] as a pointer in C#

问题描述

我有生成基于任何packet.The问题的内容的CRC校验字节是在C ++翻译功能到C＃的函数

I have a function that generates a CRC check byte based on the content of any packet.The problem is in translating the function from C++ to C#

C ++代码：

unsigned char GenerateCheckByte( char* packet, int length, unsigned long seed )
{
if( !packet ) return 0;
unsigned long checksum = 0xFFFFFFFF;
length &= 0x7FFF;
char* ptr = packet;
unsigned long moddedseed = seed << 8;
for( int i = 0; i < length; i++ )
	checksum = ( checksum >> 8 ) ^ table[moddedseed + ( ( *(ptr++) ^ checksum ) & 0xFF )];
unsigned char result = ( (checksum>>24)&0xFF ) + ( (checksum>>8)&0xFF ) + ( (checksum>>16)&0xFF ) + ( checksum&0xFF );
return result;
}

的

的char *（数据包）也可以被定义为LPBYTE，这个想法是所分配的值*数据包分配到* PTR，当你看到* PTR increases.Meaning一个字节数组中，并通过增加它转到下一个字节指针的值传递的。

the char*(packet) can also be defined as LPBYTE,the idea is that the value assigned to *packet is assigned to *ptr and as you see *ptr increases.Meaning a byte array is passed in and by increasing the value of the pointer it goes to the next byte.

我试着做它在C＃和失败了很多times.After一些艰苦的工作我想通了一些代码，但我不能执行它：

I tried to do it in C# and failed many times.After some hard work I figured out some code,but i can't execute it :?

C＃代码

    public static unsafe byte GenerateCheckByte(byte *packet, int length, UInt32 seed )
    {
        if (*packet == 0)
        return 0;
        UInt32 checksum = 0xFFFFFFFF;
        length &= 0x7FFF;
        byte *ptr = packet;
        UInt32 moddedseed = seed << 8;
        for (int i = 0; i < length; i++)
            checksum = ( checksum >> 8 ) ^ Table.table[moddedseed + ( ( *(ptr++) ^ checksum ) & 0xFF )];
        byte result = (byte)(( (checksum>>24)&0xFF ) + ( (checksum>>8)&0xFF ) + ( (checksum>>16)&0xFF ) + ( checksum&0xFF ));
        return result;
    }

它看起来并不那么糟糕，但我不能把它叫做

It doesn't look that bad,but I can't call it

  unsafe
  {
      packetBuffer[5] = Functions.GenerateCheckByte(&packetBuffer[0], 18, packet.seedCRC);
  }

错误：你只能采取不固定的表达地址的内部固定语句初始化

error: "You can only take the address of an unfixed expression inside of a fixed statement initializer"

请注意

在C ++和C＃应用程序packetbuffer为byte [] packetBuffer =新的字节[18];

packetbuffer in both C++ and C# application is byte[] packetBuffer = new byte[18];

推荐答案

您可以让该方法接受一个字节数组：

You could make the method accept a byte array:

public static unsafe byte GenerateCheckByte(byte[] packetArray, int length, UInt32 seed)
{
    fixed(byte *packet = packetArray)
    {
        ... etc
    }
}

这是更好地保持不安全的东西隐藏起来，尽可能落后管理接口

It's better to keep the unsafe stuff hidden away as much as possible behind managed interfaces.

然后调用它会很容易。

packetBuffer[5] = Functions.GenerateCheckByte(packetBuffer, 18, ...

在事实上，这将是最好编写 GenerateCheckByte 反正阵列上运行，而不是钻研<， code>不安全技巧：

In fact, it would be better to write GenerateCheckByte to operate on an array anyway, instead of delving into unsafe techniques:

public static unsafe byte GenerateCheckByte(byte[] packet, int length, UInt32 seed )
{
    if (packet == null)
        throw new ArgumentNullException("packet"); // the right way in C#

    UInt32 checksum = 0xFFFFFFFF;
    length &= 0x7FFF;

    UInt32 moddedseed = seed << 8;
    for (int i = 0; i < length; i++)
        checksum = ( checksum >> 8 ) ^ Table.table[moddedseed + ( ( packet[i] ^ checksum ) & 0xFF )];
    byte result = (byte)(( (checksum>>24)&0xFF ) + ( (checksum>>8)&0xFF ) + ( (checksum>>16)&0xFF ) + ( checksum&0xFF ));
    return result;
}

写最简单，最安全的实现就可以了，用指针只一塌糊涂，如果你发现分析的一个瓶颈。

Write the simplest, safest implementation you can, and only mess with pointers if you find a bottleneck in profiling.

您刚刚翻译了很多现有的C / C ++到C＃的？有小点，这样做，除非你从它那里得到一些新的安全性/可维护性。 ：）

Are you just translating a lot of existing C/C++ into C#? There's little point doing that unless you get some new safety/maintainability from it. :)

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