如何从Byte []创建一个单词？

Question

I am new to programming world, I want to convert two bytes into a word.

So basically, I have a Byte array where index 0 is Buffer[0]=08 and index 1 is Buffer[1]=06 I want to create a word from these two bytes

where word ETHType to be 0x0806

Answer 1

You would use bitwise operators and bit shifting.

uint16_t result = ((uint16_t)Buffer[0] << 8) | Buffer[1];

This does the following:

• The value of Buffer[0] is shifted 8 bits to the left. That gives you 0x0800
• A bitwise OR is performed between the prior value and the value of Buffer[1] . This sets the low order 8 bits to Buffer[1] , giving you 0x0806

Answer 2

word ETHType = 0;
ETHType = (Buffer[0] << 8) | Buffer[1];

edit: You should probably add a mask to each operation to make sure there is no bit overlap, and you can do it safely in one line.

word ETHType = (unsigned short)(((unsigned char)(Buffer[0] & 0xFF) << 8) | (unsigned char)(Buffer[1] & 0xFF)) & 0xFFFF;

Answer 3

Here's a macro I use for this very thing:

#include <stdint.h>

#define MAKE16(a8, b8) ((uint16_t)(((uint8_t)(((uint32_t)(a8)) & 0xff)) | ((uint16_t)((uint8_t)(((uint32_t)(b8)) & 0xff))) << 8))