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　　做单片机开发或者芯片开发，不可避免地要用到C或者C++，这篇文章是2019年做开发时写的文章，发在CSDN上，展现量是23980，阅读量是13111，收藏量是37，说明对有些开发者还是有用的，就发在今日头条上。

　　先在VC++6.0编程环境中编写测试代码。

　　源程序：

#include <stdio.h>
#include "string.h"
 
int main(int argc, char* argv[])
{    
	  unsigned int Data_Uint32=0x12345678;
	  unsigned short int Data_Uint16_1,Data_Uint16_2;
	  unsigned char Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4;
	  struct StructByte8{
		  unsigned char Byte01:1;
		  unsigned char Byte02:1;
		  unsigned char Byte03:1;
		  unsigned char Byte04:1;
		  unsigned char Byte05:1;
		  unsigned char Byte06:1;
		  unsigned char Byte07:1;
		  unsigned char Byte08:1;
	  } Test1;
      unsigned char C1[]="A";
      //定义16位的指针将32位地址强制转为16位，高位丢弃取低位
	  unsigned short int *p16=(unsigned short int *)(&Data_Uint32);
	  unsigned short int Data_Uint16_2p,Data_Uint16_1p;
 
	  printf("32位整数：0x%x\n",Data_Uint32);
	  printf("-------------------通过指针运算-------------------\n");
	  Data_Uint16_2p=*(unsigned short int *)p16;
	  Data_Uint16_1p=*((unsigned short int *)p16+1);
	  printf("转换后的16位整数：0x%x,0x%x\n",Data_Uint16_1p,Data_Uint16_2p);
 
	  Data_Uint8_1= *(unsigned char *)p16;
	  Data_Uint8_2= *((unsigned char *)p16+1);
	  Data_Uint8_3= *((unsigned char *)p16+2);
	  Data_Uint8_4= *((unsigned char *)p16+3);
	  printf("转换后的8位整数：0x%x,0x%x,0x%x,0x%x\n",Data_Uint8_1,Data_Uint8_2,
                                                     Data_Uint8_3,Data_Uint8_4);
	  Data_Uint8_1=0;Data_Uint8_2=0;Data_Uint8_3=0;Data_Uint8_4=0;
	  //直接根据指针取值
	  //将32位的整数分解成两个16位的整数,再取低位的16位
	  //强制转换，丢弃高位的16位
	  //32位转16位
	  Data_Uint16_1=(unsigned short int)(Data_Uint32>>16);
	  Data_Uint16_2=(unsigned short int)Data_Uint32;
 
	  //32位转8位
	  Data_Uint8_1= (unsigned char)(Data_Uint32>>24);
	  Data_Uint8_2= (unsigned char)(Data_Uint32>>16);
	  Data_Uint8_3= (unsigned char)(Data_Uint32>>8);
	  Data_Uint8_4= (unsigned char)Data_Uint32;
 
	  printf("-------------------通过位运算-------------------\n");
	  printf("转换后的16位整数：0x%x,0x%x\n",Data_Uint16_1,Data_Uint16_2);
	  printf("转换后的8位整数：0x%x,0x%x,0x%x,0x%x\n",Data_Uint8_1,Data_Uint8_2,
                                                    Data_Uint8_3,Data_Uint8_4);
	  
	  printf("-------------------通过结构运算-------------------\n");     
	  printf("字符A，ASCII为01000001，结构转换后的内容\n");  
      memcpy(&Test1, C1, sizeof(Test1));  
	  printf("Test1.Byte08=%d \n",Test1.Byte08);  
	  printf("Test1.Byte07=%d \n",Test1.Byte07);  
	  printf("Test1.Byte06=%d \n",Test1.Byte06);  
	  printf("Test1.Byte05=%d \n",Test1.Byte05);  
	  printf("Test1.Byte04=%d \n",Test1.Byte04);  
	  printf("Test1.Byte03=%d \n",Test1.Byte03);  
	  printf("Test1.Byte02=%d \n",Test1.Byte02);  
	  printf("Test1.Byte01=%d \n",Test1.Byte01);  
      
	  Data_Uint8_1=0x89;Data_Uint8_2=0xAB;Data_Uint8_3=0xCD;Data_Uint8_4=0xEF;
	  printf("-------------------通过位运算合并-------------------\n");
	  Data_Uint16_1 = (unsigned short int)(Data_Uint8_1 << 8) | (unsigned short int)(Data_Uint8_2);
	  Data_Uint16_2 = (unsigned short int)(Data_Uint8_3 << 8) | (unsigned short int)(Data_Uint8_4);
	  Data_Uint32=(unsigned int) (Data_Uint16_1 << 16) | (unsigned int)(Data_Uint16_2);
	  printf("合并前的8位整数：0x%x,0x%x,0x%x,0x%x\n",Data_Uint8_1,Data_Uint8_2,Data_Uint8_3,Data_Uint8_4);
	  printf("合并后的16位整数：0x%x,0x%x\n",Data_Uint16_1,Data_Uint16_2);
	  printf("合并后的32位整数：0x%x\n",Data_Uint32);
 
	return 0;
}

　　输出：

　　进入Keil uVision5（做芯片开发一般常用工具）编程，接着写，就是直接强制转换：

	  printf("-------------------8位到32位转换-------------------\n");
	  Data_Uint8_1=0x00;
	  Data_Uint8_2=0x19;
	  Data_Uint16_2=0x00;
	  Data_Uint16_1 = (unsigned short int)(0x00 << 8) | (unsigned short int)(Data_Uint8_2);
      Data_Uint32=(unsigned int) (0x00 << 16) | (unsigned int)(Data_Uint16_1);
	  printf("转换前的8位整数：0x%x,%d\n",Data_Uint8_2,sizeof(Data_Uint8_2));
	  printf("8位到32位转换1======>转换后的32位整数：0x%x,数据长度：%d\n",Data_Uint32,sizeof(Data_Uint32));
	  Data_Uint32=(unsigned int) (0x00 << 16) | (unsigned int)( (unsigned short int)(0x00 << 8) | (unsigned short int)(Data_Uint8_2));
	  printf("8位到32位转换2======>转换后的32位整数：0x%x,数据长度：%d\n",Data_Uint32,sizeof(Data_Uint32));
	  //Data_Uint32=(unsigned int) (0x00 << 24) | (unsigned int)(Data_Uint8_2);
	  Data_Uint32= (unsigned int)(Data_Uint8_2);
	  printf("8位到32位转换3======>转换后的32位整数：0x%x,数据长度：%d\n",Data_Uint32,sizeof(Data_Uint32));
      Data_Uint32=0x69;
      Data_Uint8_1= (unsigned char)(Data_Uint32);
	  printf("32位整数：0x%x,数据长度：%d\n",Data_Uint32,sizeof(Data_Uint32));
	  printf("32位到8位转换======>转换后的8位整数：0x%x,数据长度：%d\n",Data_Uint8_1,sizeof(Data_Uint8_1));

　　实际输出：

　　-------------------8位到32位转换-------------------

　　转换前的8位整数：0x19,1

　　8位到32位转换1======>转换后的32位整数：0x19,数据长度：4

　　8位到32位转换2======>转换后的32位整数：0x19,数据长度：4

　　8位到32位转换3======>转换后的32位整数：0x19,数据长度：4

　　32位整数：0x69,数据长度：4

　　32位到8位转换======>转换后的8位整数：0x69,数据长度：1

　　说明：8位强制转32位，前面系统自动加了24位的0；32位强制转8位，系统只截取了最后的8位。

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