将2个字节转换为整数

Question

我收到一个端口号为2个字节(最低有效字节优先),我想将它转换为一个整数,以便我可以使用它.我做了这个:

char buf[2]; //Where the received bytes are

char port[2];

port[0]=buf[1]; 

port[1]=buf[0];

int number=0;

number = (*((int *)port));

但是,有一些错误,因为我没有得到正确的端口号.有任何想法吗？

Answer 1

I receive a port number as 2 bytes (least significant byte first)

You can then do this:

  int number = buf[0] | buf[1] << 8;

Answer 2

If you make buf into an unsigned char buf[2], you could just simplify it to;

number = (buf[1]<<8)+buf[0];

Answer 3

我很高兴已经对此做出了合理回答。但是，另一种技术是在代码中定义宏，例如：

// bytes_to_int_example.cpp
// Output: port = 514

// I am assuming that the bytes the bytes need to be treated as 0-255 and combined MSB -> LSB

// This creates a macro in your code that does the conversion and can be tweaked as necessary
#define bytes_to_u16(MSB,LSB) (((unsigned int) ((unsigned char) MSB)) & 255)<<8 | (((unsigned char) LSB)&255) 
// Note: #define statements do not typically have semi-colons
#include <stdio.h>

int main()
{
  char buf[2];
  // Fill buf with example numbers
  buf[0]=2; // (Least significant byte)
  buf[1]=2; // (Most significant byte)
  // If endian is other way around swap bytes!

  unsigned int port=bytes_to_u16(buf[1],buf[0]);

  printf("port = %u \n",port);

  return 0;
}