很好用的C++在线编译器: http://www.dooccn.com/cpp/
很好用的C++编译器(有时候第一个库没有就用这个):http://cpp.sh/
很好用的在线计算器:http://cal.apple886.com/index2.htm
很好用的CRC计算器:https://www.lammertbies.nl/comm/info/crc-calculation.html
经常用的结构体对齐:
#pragma pack (1) // C编译器将按照1个字节对齐。
#pragma pack () // 结束自定义字节对齐方式。
#pragma pack (push,1) // 把原来对齐方式设置压栈,并设新的对齐方式设置为一个字节对齐
#pragma pack(pop) // 结束对齐状态
结构体地址分配与用法:
#include <iostream>
using namespace std;
#pragma pack(1)
typedef struct {
long head;
long type;
int length;
int yaw_angle; // 航向角度*100
int crc;
} heading2gimbal_t;
#pragma pack()
int main()
{
heading2gimbal_t heading2;
long * pI = &(heading2.head);
/*第一个地址*/
cout<< (long*)&heading2 << endl;
cout<< &(heading2.head)<< endl;
/*第二个地址*/
cout<< &(heading2.type)<< endl;
cout<< (long*)&heading2 +1<< endl;
cout<< ++ pI<< endl;
/*第三个地址*/
cout<< &(heading2.length)<< endl;
cout<< ++ pI<< endl;
/*指向结构体的指针加1,地址实际上增加的值为结构体的大小,及结构体的字节数*/
cout<< &heading2 << endl;
cout<< &heading2 +1 << endl;
/* 每次按照初始大小自增(设为uint8_t就能通过协议传输了)*/
cout<< pI<< endl;
cout<< ++pI<< endl;
cout<< ++pI<< endl;
cout<< ++pI<< endl;
cout<< ++pI<< endl;
return 0;
}
Output:
0x7ffffc2fd140
0x7ffffc2fd140
0x7ffffc2fd148
0x7ffffc2fd148
0x7ffffc2fd148
0x7ffffc2fd150
0x7ffffc2fd150
0x7ffffc2fd140
0x7ffffc2fd15c
/* 每次按照初始大小自增*/
0x7fff31b6e070
0x7fff31b6e078
0x7fff31b6e080
0x7fff31b6e084
0x7fff31b6e088
十六位数与八位数的转换(uint16_t (unsigned char)—— uint8_t(unsigned char))
- 一个16位数unit拆分成2个8位数high、low:
high = (unit >> 8) & 0xff; //高8位
low = unit & 0xff; //低8位
- 2个8位数high和low合成一个16位数据unit:
unit = (uint16_t) (high << 8) | low; //uint16_t是无符号16位
字节序(大小端)
- 字节序,顾名思义字节的顺序,再多说两句就是大于一个字节类型的数据在内存中的存放顺序。
- Little-Endian就是低位字节排放在内存的低地址端,高位字节排放在内存的高地址端。
- Big-Endian就是高位字节排放在内存的低地址端,低位字节排放在内存的高地址端。
Big-Endian: 低地址存放高位,如下图:
栈底 (高地址)
0x4003 buf[3] (0x78) -- 低位
0x4002 buf[2] (0x56)
0x4001 buf[1] (0x34)
0x4000 buf[0] (0x12) -- 高位
栈顶 (低地址)
Little-Endian: 低地址存放低位,如下图:
栈底 (高地址)
0x4003 buf[3] (0x12) -- 高位
0x4002 buf[2] (0x34)
0x4001 buf[1] (0x56)
0x4000 buf[0] (0x78) -- 低位
栈顶 (低地址)
注意:
- 在现有的平台上Intel的X86采用的是Little-Endian,而像Sun的SPARC采用的就是Big-Endian。
- 0xff10 左高右低
那么很简单判断是哪种模式:
#include <iostream>
#include "stdio.h"
using namespace std;
#pragma pack(1)
typedef struct {
char head;
char type;
short length;
short yaw_angle; // 航向角度*100
// short crc;
} heading2gimbal_t;
#pragma pack()
// CRC16
static unsigned short const wCRC16Table[256] = {
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040};
void CRC16(const unsigned char* pDataIn, int iLenIn, unsigned short* pCRCOut)
{
unsigned short wResult = 0;
unsigned short wTableNo = 0;
int i = 0;
for( i = 0; i < iLenIn; i++)
{
wTableNo = ((wResult & 0xff) ^ (pDataIn[i] & 0xff));
wResult = ((wResult >> 8) & 0xff) ^ wCRC16Table[wTableNo];
}
*pCRCOut = wResult;
}
void get_value(){
unsigned short crc16_result;
heading2gimbal_t heading;
heading.head = 0xAA;
heading.type = 0x01;
heading.length = 0x01;
heading.yaw_angle = 0x12;
// calc_crc16(( char *)&heading, 6);
CRC16(( unsigned char *)&heading, 1, &crc16_result);
cout<< hex <<crc16_result<< endl;
cout<< hex <<((crc16_result >> 8) & 0xff)<< endl;
cout<< hex << (crc16_result & 0xff)<< endl;
cout<< sizeof(heading)<< endl;
cout<< hex <<((unsigned char) crc16_result == 0x80) <<endl;
}
int main(){
get_value();
return 0;
}
output:
// 由最后输出的1来判定为小端模式
7f80 7f 80 6 1
强制类型转换(int)、(int&)、(int*)和int* 的区别
(int)x 强制类型转换,是将浮点数x为参数构造整数(即float转换为int)
(int &)y 则是告诉编译器将y看成int对待(内存里的数据不做任何转换),所以(int &)x值为1071 644 672,为浮点数存储在内存中的值。
int* 为定义int指针变量,如:int* a = NULL;
(int*) 类型转换成整型指针,如:int* a = (int*)b;