如何将两个字节作为一个int（或类似的东西）存储在BYTE数组中？

Question

I am writing a bittorrent client in C++ that receives a message from a tracker (server) containing several 6 byte strings. The first 4 bytes represent the IP address of a peer and the next 2 bytes represent the port number that the peer is listening on.

I have worked out how to convert the ip bytes into a human readable ip address but am struggling to convert the two bytes representing the port number into an int (or something similar)

Here are my efforts so far:

BYTE portbinary[2];
unsigned short peerport;

//trackers[i]->peersBinary[j * 6 + 4] is the first byte
portbinary[0] = trackers[i]->peersBinary[j * 6 + 4];
//trackers[i]->peersBinary[j * 6 + 5] is the second byte
portbinary[1] = trackers[i]->peersBinary[j * 6 + 5];
peerport = *portbinary;

Upon examination peerport only seems to contain the integer representation of the first byte, how might I be able to fix this?

Thanks in advance :)

Answer 1

我更喜欢使用按位运算而不是类型修剪，因为它根本不会引起字节序问题（端口号是大字节序号，当今许多系统都是小字节序）。

int peerport = (portbinary[0] << 8) | portbinary[1];

Answer 2

由于看起来数据已经对齐，因此您可以使用

peerport = ntohs(*(uint16_t *)(trackers[i]->peersBinary + j * 6 + 4));

Answer 3

Since portbinary is an array of BYTE , then *portbinary is equivalent to portbinary[0] .

A portable way to to achieve your result could be:

peerport = portbinary[0];
peerport = 256*peerport + portbinary[1];

This assumes portbinary was delivered in network byte order.

Answer 4

Solution with unions:

union port_extractor
{
    BYTE raw_port[2];
    unsigned short port_assembled;
};

This will work if your computer endianess is the same as of representation you fetch from the network. Sorry, I dont know how it comes by bittorrent protocol.

If the endianess is the opposite, then the solution you are bound to use is not as nice:

unsigned short port_assembled = (unsigned short)raw_port[first_byte] | ((unsigned short)raw_port[second_byte] << 8);
// first_byte = 0, second_byte = 1 or vice versa 
// depending on source data endianess